Diamonds Flashcards
(350 cards)
1
Q
What is the significance of the Argyle mine?
A
the Argyle mine in Australia—caused dramatic growth in India’s diamond cutting industry, which processes large numbers of inexpensive diamonds. This made diamonds available to a wider consumer base.
2
Q
Why are diamond grades important?
A
Diamond grades make it possible for people to discuss diamonds simply and concisely. Diamond grades can help you compare one diamond with another.
3
Q
What are diamond grades used for?
A
Diamond grades have many different uses. For gemological laboratories, grades are simply statements of diamond quality. Some people use grades to determine value and to decide whether or not to buy, or to match diamonds for jewelry. A diamond grade might be part of an appraisal, as one step in the evaluation of a finished piece of jewelry.
4
Q
What are diamond reports used for?
A
A quality report from a reputable lab allows a retailer or dealer to choose a diamond without seeing it.
A report can also work the other way: You can check a diamond that’s accompanied by a quality report to make sure it matches its description. This protects you against switched stones.
5
Q
What are wholesale price lists for?
A
a diamond professional can compare a diamond’s quality report to its listed value, determine the diamond’s fair price, and decide whether or not to buy or sell it.
The suggested prices depend very strongly on the market conditions that exist at a particular time.
6
Q
How are small low quality diamonds graded?
A
it’s not worthwhile to spend a lot of time grading small, low- quality stones. A quick examination under a loupe is usually all they get.
7
Q
How are small diamonds sorted and graded?
A
Small diamonds are often sorted rather than graded individually because it isn;t cost effective to grade them individually.
So the dealer might put them through a series of sieves and sort them by size, and then sort the various sizes into smaller piles based on color. The dealer might not even look for clarity characteristics. Parcels of melee are usually sold by clarity range—if the supplier is reputable, the dealer can trust that the diamonds in the parcel will be within the requested clarity range.
8
Q
What are the benefits of having precisely matched diamonds in jewelry?
A
It’s easier to sell a well-finished piece of jewelry containing precisely matched diamonds—no matter what their clarity grade—because you can justify its price to your customers.
9
Q
What is the most common type of appraisal?
A
The most common type is an appraisal for insurance replacement. This contains a description of the jewelry—everything from the Four Cs of the gems to the jewelry’s design to the karat weight of the metal. An insurance company can use the appraisal to replace the item if it’s lost or stolen.
Insurance replacement appraisals include a value for the jewelry item. That value might be quite different from an appraisal done to determine its liquidation value. Liquidation appraisals apply a value to the item for immediate sale.
10
Q
Why are good quality diamonds so valuable?
A
The unique physical properties of gem-quality diamonds allow them to survive environmental forces better than any other gemstone.
11
Q
How did abundant new diamond supplies affect the market?
A
Wider availability of diamonds to the public
12
Q
When did India start trading diamonds and to whom?
A
4th century BC to India’s wealthy
13
Q
When was the first South African Kimberline pipe discovered?
A
late 1800s
14
Q
What is single channel marketing?
A
A direct, centrally controlled marketing route for rough diamonds
15
Q
What is the Central Selling Organisation?
A
An agency designed to purchase, sort, evaluate, and sell rough diamonds.
For decades, the CSO served as the marketing and distribution channel for rough diamonds from mines all over the world.
16
Q
How did the story of Africa’s Diamonds begin?
A
The story of Africa’s diamonds began in 1866 with the discovery of a 21.25-ct. rough diamond on a farm south of Kimberley, South Africa. There is evidence of other discoveries, some as early as 1854. But the “Eureka,” as it was called, was the first to be authenticated.
17
Q
What diamond started the rush in South Africa and where what is found?
A
The Star of the South was found in the Vaal river in 1869
18
Q
What is a digger?
A
An independent diamond prospector
19
Q
What is soft, diamond bearing ground near the surface called?
A
yellowground
20
Q
What’s underneath yellowground?
A
blueground
21
Q
Who consolidated all the mines in the Kimberly area into DeBeers Consolidated Mines LLC in 1888?
A
Cecil Rhodes
22
Q
How much of the world’s diamond supply did DeBeers control by 1900?
A
By 1900, De Beers controlled an estimated 90 percent of the world’s production of rough diamonds. With what amounted to a production monopoly, Rhodes had reached his goal of controlling prices by controlling the supply
23
Q
Who were the London Diamond Syndicate?
A
A group of diamond merchants that united in 1890 to buy and sell rough diamonds.
24
Q
What was DeBeers marketing strategy?
A
Strong global advertising, supported by an annual budget that has reached as high as US$200 million per year
A diamond stockpile, maintained and released selectively to balance supply and demand
A worldwide network of outside buying offices
Quota provisions in the contracts with its CSO partners that allowed equal sharing of oversupply challenges
Control over distribution through a strong client network
25
What's the diamond pipeline?
The path diamonds followed from the mine to the consumer.
26
What are sights?
Trading event where selected clients buy rough diamonds.
27
What are sightholders
A diamond manufacturer or dealer invited by De Beers to buy rough diamonds.
28
What are specials?
A rough diamond over 10.80 cts., sold separately to a sightholder who specializes in larger stones.
29
Why did DeBeers begin to buy rough from other producers?
to safeguard diamond prices and ensure market stability
30
What led to the collapse of the single-channel rough diamond market?
when important diamond producers in Russia, Australia, and Canada sought more control over their own mineral resources, negotiations over trade contracts became more complex and costly for De Beers. The situation was complicated even more by an overall increase in diamond production, which limited the CSO’s ability to control supply and demand. The multi-channel rough diamond market that emerged consisted primarily of Russia, private mining companies in Australia and Canada, and a few independent diamond-trading companies.
The multi-channel rough diamond market has become a fact of life in the diamond industry. This assignment will examine what each of the new channels looks like and what measures De Beers has taken to adjust to this new reality.
▶ VIDEO: Diamond Pipelines
▶ VIDEO: Russell Shor: Changes in Rough Diamond Distribution
31
What is vertical integration
Involvement of a business or industry in all aspects of its product’s market.
32
Why does vertical integration increase profits
Vertical integration in the diamond industry increases profits because there’s much more value in a finished piece of diamond jewelry than in a rough diamond crystal.
33
Where is the Mir mine
Siberia
34
who owns the Argyle mine?
Rio Tinto
35
What is beneficiation
is a mining term that refers to the process of reducing and separating extracted ore into mineral and waste. In a social context it means that a portion of the natural resources extracted from a country’s soil must stay in the country to support its economic growth. Modified versions of this practice already existed in other places, such as Canada, but the concept of beneficiation is most closely associated with the diamond-producing nations of Africa.
36
What is the supplier of choice program?
De Beers and its sightholders would work together to market and sell diamonds. For decades, De Beers had provided much of the industry’s advertising—up to $200 million per year. But the company recognized that the amount spent on diamond promotion was less than the amount spent on promotion of other luxury goods—only 1 percent of sales compared to 10 to 20 percent. So De Beers began requiring its sightholders to create their own diamond-marketing efforts
37
What are the best practices principles?
One of the declared principles is to uphold the highest professional and ethical standards. De Beers insisted on a similar commitment from each of its sightholders.
De Beers revised its BPP to incorporate its commitment to the KP as well as other diamond trading issues that touch on the unjust treatment and suffering of people. The 2007 edition of the BPP imposed strict trading and disclosure practices on De Beers and its trading partners. The issues included human rights, child labor, forced labor, and money laundering to fund terrorist activities.
38
What is the Jeweler's Vigilance Committee?
a non-profit trade association dedicated to ensuring legal compliance within the jewelry industry.
39
What is a diamond bourse?
A place in a diamond trading center where diamond dealers meet to sell, trade, and share industry news.
40
What is the World Diamond Council?
WDC came into being in July 2000. It represents the world’s most significant diamond trading centers, manufacturers, and jewelers, and also assists with the implementation of the Kimberley Process.
Stephane also deals with issues involving the diamond trading center of Antwerp, lab-grown diamond nomenclature, and the current economic situation
41
Who dominated the gem trade in the middle ages?
Antwerp
42
What diamond cutting does Tel Aviv specialize in
large diamonds and precision fancy cuts
43
what kind of diamonds are cut in NYC
Large, high quality stones
44
what kind of diamonds does China specialize in cutting?
small, well cut rounds. high quality PC's below .20ct
45
What are the earth's 3 layers?
crust, mantle, core
46
what temp and pressure do diamonds form under?
a temperature range of 2102°F to 2192°F (1150°C to 1200°C) and pressure between 50 kilobars and 70 kilobars.
47
what is a kilobar?
A kilobar is a unit that scientists use to measure extremely high pressure
48
Where do diamonds form?
In the upper mantle 90 to 140 miles beneath the surface
49
Where do the best temperature and pressure conditions for diamond formation exist?
Under Cratons. Cratons are the oldest sections of the landmasses. They make up the interior portions of the continents, where they’ve existed without change for millions of years.
50
Are there cratons in the ocean?
No
51
What 2 types of rock do diamonds form in?
Peridotite (igneaous) and eclogite(metamorphic)
52
What is igneous rock?
Igneous rocks start out in a molten or partially molten state and become solid when they cool
53
What is metamorphic rock
Metamorphic rocks are pre-existing rocks that have been altered by heat and pressure
54
what is peridotite?
Peridotite, where most diamonds form, probably came into existence soon after the earth first formed. Peridotite contains the most ancient source of the earth’s carbon, which is released by circulation that takes place in the mantle. Because there’s plenty of available material, the carbon-releasing process is fairly constant. To scientists, this means that the carbon needed for diamond formation is always present. It also means that diamond formation might be happening, miles beneath you, as you read this.
55
what is eclogite
Eclogite’s carbon is contained in ancient rocks that are closer to the earth’s surface. Eclogite is a younger rock than peridotite, and occurs at much shallower levels. Its carbon comes partly from organic matter that didn’t exist when the earth first formed. This organic matter becomes part of the eclogite, and its carbon is released when the crustal rocks that contain it are dragged deep into the earth in a process called subduction.
56
What is subduction
Subduction occurs when two of the earth’s crustal plates collide and one is forced under the other. The lowered plate heats up, causing its component minerals to melt and release their trapped carbon. Because it’s dependent on this process, the release of carbon from eclogite isn’t constant. Eclogite’s diamonds tend to be younger than peridotite’s diamonds.
57
What are plate tektonics?
The study of the formation, structure, and movement of the earth’s landmasses
58
What kind of rocks are diamond deposits found in?
Kimberlite and Lamproite
59
What is emplacement?
A geologic process that delivers materials (sometimes diamonds) to the surface.
60
What is a pipe?
A deep vertical formation at the earth’s surface that results from a kimberlite or lamproite emplacement.
61
How do you measure the age of rocks?
The minerals in a rock might contain radioactive elements. If they do, those elements give off atomic particles as they decay. As a radioactive element emits its atomic particles, it gradually changes to another form of the same element or to a different element: Scientists call it a “daughter” or end product.
62
How can you measure a diamond's age?
Radiometric dating the inclusions in diamonds. You can't date diamonds themselves.
63
What's a primary deposit
Gems found in the rock that carried them to the surface
64
What are secondary deposits?
Gems found away from their primary source.
65
What are alluvial deposits?
Deposits found in rivers and streams
66
What are indicator minerals?
Minerals formed together with diamonds at great depths and brought to the surface by the same kimberlites or lamproites.
67
What is open pit mining?
Removal of mineral-bearing ore from a large surface excavation.
68
What is overburden?
Sand, gravel, or rock that covers a diamond pipe. Must be removed to reach diamond-bearing ore.
69
What is block caving?
Underground mining that involves building a concrete-lined tunnel under an ore deposit, then collecting the ore through openings in the liner
70
what is a drift?
A horizontal tunnel drilled through a diamond pipe.
71
What is recovery?
Any method used to separate diamonds from ore or alluvial sediments.
72
What is primary crushing?
Any method used to separate diamonds from ore or alluvial sediments.
73
What is a scrubber?
An apparatus that washes away dirt and clay from diamond-bearing ore.
74
What is dense media separation?
A recovery process that separates diamonds from lighter material. Also called heavy media separation.
75
What's a grease belt?
An apparatus that uses diamonds’ affinity for grease to separate them from other minerals.
76
What is xray separation?
A recovery method that uses X-rays to detect diamonds and an air jet to remove them from ore.
77
How do marine deposits form?
Marine deposits result when diamond-bearing kimberlite pipes erode, releasing their diamonds. Flowing rivers then carry the diamonds to the coast.
78
Where is the largest marine deposit?
Namibia
79
What is the measurement of a mine's productivity
carats per hundred metric tons
80
What leads to a profitable mine?
The diamonds must form in the mantle, they must be in the right location to be brought to the surface, they must survive the heat and pressure of transport, and they must remain in a location where they’ll be discovered. Once discovered, there must be enough of them to support a mining enterprise for many years. Because this combination of conditions is so specific, potentially profitable diamond sources are rare.
81
What is a crystal
Solid matter with atoms arranged in a regular, repeating pattern.
82
define crystalline
Composed of crystals or related to crystals.
83
what is a mineral
A mineral is a solid material that forms in nature, not as the result of human technology
84
what is inorganic?
It's not alive and never was
85
what is a species?
Minerals related by chemical composition and crystal structure
86
what's a covalent bond?
A chemical bond formed by two atoms sharing electrons. It is the strongest bond
87
What's a tetrahedron?
In diamond, a group of five carbon atoms with one at the center.
88
what's a unit cell
Smallest group of atoms with the characteristic chemical composition and the basic crystal structure of a mineral.
89
Why do diamonds have superior hardness?
The carbon atoms in diamond bond under very high pressure and create a strong, interlocking atomic structure. Diamond’s atoms are closer together than the atoms of any other natural material. This is what gives diamond its superior hardness.
90
what is crystal shape or form?
Geometric shape of a well-formed crystal.
91
What is habit?
Characteristic crystal shape of a specific mineral.
92
what is the habit of gem diamond?
octahedron
93
What is a glassie?
A well-shaped, transparent, octahedral diamond crystal with sharp, square edges.
94
What is crystal structure/lattice?
Regular, repeating arrangement of atoms in a mineral.
95
What are crystal systems?
Categories of crystals based on their symmetry and internal structure.
96
What are some examples of cubic/isometric minerals?
Diamond, Garnet, spinel, platinum, and gold are also cubic minerals
97
What are characteristics of the cubic/isometric system?
The cubic system is the most symmetrical: Well-formed cubic crystals are evenly proportioned and balanced.
98
How is diamond crystal structure important to cutters?
In some directions, the atoms in a diamond crystal are closer together than in others. This makes those directions harder and, as a result, unsuitable for sawing and polishing.
99
What is specific gravity
Ratio of the weight of a material to that of an equal volume of water
100
What is singly refractive/isotropic mean?
Possessing the same physical or optical properties in all crystal directions. light rays behave the same no matter which direction they are traveling - characteristic of cubic crystal structures
101
What is doubly refractive/anisotropic
Possessing different physical or optical properties in different crystal directions. Crystals that form in less symmetrical crystal systems split light rays into separate beams that take different paths and travel at different speeds.
102
What is optic character?
The way a mineral handles light
103
What is doubling?
In A doubly refractive mineral, you will see a copy of the facet junction
104
What trace element produces yellow color in diamond?
Nitrogen
105
What is a trace element?
Atoms in a gem that aren’t part of its essential chemical composition.
106
What element turns diamonds blue and makes them electrical conductors?
Boron
107
what is a glide plane?
Crystal distortion caused during growth when one part of the lattice is offset in relation to the rest. It happens when the atoms don’t stack perfectly during growth and the crystal structure becomes deformed.
108
What is graining?
Visible, shadow-like lines in a diamond caused by irregularities in the crystal structure. Occurs when conditions change during crystal growth
109
What is Bort?
Bort is a form of diamond that usually occurs as very included single crystals in a range of yellows, grays, and browns - usually industrial use
110
What is the most valuable characteristic of rough diamonds?
In the gem-quality category, the shape of a rough diamond crystal is the most important factor in its potential value as a gemstone. Two crystals with the same color and clarity might be equal in weight, yet one can be worth many times more than the other on the basis of shape alone.
111
What is thermal expansion
Capacity of a material to expand when it’s heated.
112
What is thermal conductivity?
The relative ability of a material to transfer heat.
113
What are crystal planes?
Internal directions parallel to a mineral’s unit cell surfaces. they produce properties like directional hardness and cleavage.
114
What are diamonds 3 crystal planes?
cubic, octahedral, and dodecahedral. All diamonds, regardless of their external appearance, contain all three. These planes are important to a diamond cutter because some are best for sawing and polishing and others for cleaving.
115
what crystal plane is most efficient for sawing diamond rough?
cubic
116
What is a cleavage plane?
Plane parallel to a possible crystal face, where a diamond can split cleanly when struck.
117
What surfaces are the hardest on a diamond?
Surfaces parallel to the octahedral planes are also the hardest. They are very resistant to scratching and impossible to polish
118
What is a twinned crystal?
Crystal consisting of two or more intergrown crystals with opposing crystal directions.
119
What is a macle?
A flat, triangular twinned diamond crystal.
120
What are growth marks?
Growth marks are surface features that reflect a crystal’s development. Researchers believe that some types of growth marks are indentations that form when conditions change and cause the crystal to partially dissolve.
121
What are trigons?
little triangular depressions—occur on octahedral faces. They point in the opposite direction from the point of the crystal’s triangular face
122
What growth marks do cubic faces have?
Cubic faces can have square or rectangular depressions oriented at a 45° angle to the square face outline.
123
What growth marks to dodecahedral faces have?
Dodecahedral faces often have parallel grooves running corner to corner in the longest direction.
124
What are aggregates?
Aggregates are solid masses of individual, randomly oriented crystals. The crystals have the same internal atomic patterns, and they’ve either grown together or they’re cemented by some sort of natural binding agent.
125
What is Carbonado
is a diamond aggregate that’s used as an industrial abrasive. It can be black, gray, or brown. Because its minute diamond crystals are intergrown, carbonado is the toughest form of diamond
126
What is gem quality diamond rough?
Gem-quality diamond rough tends to have the most uniform shape. It’s usually transparent, with a shiny to slightly rough surface. Near-gem diamond rough has transparent portions that can be removed and processed by cleaving, sawing, or lasering. It might also be of a less desirable color, such as brown, but still have potential as a fashioned gem.
127
What is a makeable?
A makeable, or whole stone, is diamond rough that can be polished without sawing, cleaving, or splitting
128
What is a splittable or clivage?
A splittable, or clivage, is diamond rough that can be divided into small, but valuable, segments by lasering or cleaving.
129
What's a flat
A flat is a flat crystal that’s very limited in its potential shape.
130
What 3 optical effects give a diamond its beauty?
Brightness, fire, scintillation
131
What is brightness
The effect of all the diamond’s internal and external reflections of white light.
132
What is fire?
The flashes of color you see in a polished diamond.
133
What is scintillation?
The flashes of light and the contrasting dark areas you see when the diamond, the light, or the observer moves.
134
What are proportions and why do they matter?
The angles and relative measurements of a polished gem and the relationships between them. have a dramatic effect on how light performs when it strikes that diamond. The cutter’s choice of faceting style and proportions converts diamond rough into a beautiful, dazzling gem.
135
What are the parts of a round brilliant?
Crown—Top part of a faceted gem, above the girdle.
Table facet—Facet at the top of the crown; usually the largest facet on the stone.
Upper half facets—Facets that extend from the girdle edge toward the table.
Bezel facets—Kite- or diamond-shaped facets between the table and the girdle.
Star facets—Facets that extend from the table edge toward the girdle.
Girdle—Narrow section that forms the boundary between a stone’s crown and pavilion.
Lower half facets—Facets that extend from the girdle edge toward the culet.
Pavilion—Lower part of a faceted gem, below the girdle.
Pavilion main facets—Kite- or diamond-shaped facets between the girdle and the culet.
Culet—Small facet at the bottom of the diamond, where the pavilion mains meet. Its purpose is to protect loose diamonds against abrasion and chipping.
136
What's a wavelength?
The distance between two adjacent high points of an energy wave.
137
What is reflection?
The bouncing back of light when it strikes a surface
138
What is transmission
The passage of light into or through a material.
139
What is angle of incidence?
The angle at which a ray of light strikes a surface, measured from the normal.
140
What is the angle of reflection?
the angle at which the light bounces off
141
What is the normal?
An imaginary line perpendicular to the point where a ray of light strikes the surface.
142
what does the speed of light slow to when passing through diamond?
77,000 mps
143
What is refraction
change in speed and possible change in direction of light as it travels from one material to another
144
what is refractive index
A measure of the change in the speed and angle of light as it passes from one material to another
145
What is critical angle?
Angle between the normal and the maximum angle of refraction, which is the largest angle at which rays inside the diamond can escape.
146
What is dispersion?
An optical property that’s the difference between the RI values of specific violet and red wavelengths of visible light for a given material.
147
What is luster?
The appearance of a material’s surface in reflected light.
148
What is adamantine?
The highest degree of luster possible in a transparent material. Diamond-like
149
What gems have a subadamantine luster?
Garnets, zircons,
150
What is vitreous luster
glass like
151
What is fire and what causes it?
A display of dispersion. Fire results from the arrangement of a diamond’s facets and the angles between them. So, although every diamond has the same dispersion value, not every diamond shows the same amount of fire. Four factors of the interaction between diamonds and light contribute to the fire you see in the face-up view of a diamond.
152
what are the two components of scintillation
sparkle and pattern. Sparkle appears as flashing spots of light. In an attractive diamond, they’re evenly distributed and balanced in size. Pattern is the relative size, arrangement, and contrast of the bright and dark areas, as seen in the face-up position.
153
what is symmetry?
The exactness of a finished gem’s shape and the placement of its facets.
154
What is polish
The overall condition of the facet surfaces of a finished diamond.
155
What is light?
Light is a form of radiant energy that travels in waves.
156
does the angle of incidence always equal the angle of reflection?
yes
157
What happens to light rays that enter at the maximum angle of refraction?
They form a critical angle cone inside the diamond
158
When did rough diamonds first appear in Europe?
4th century BC
159
When did cut diamonds first appear in Europe?
1380
160
What was the earliest diamond cut
Point cut
161
When were table cuts popular and what are they?
They came after point cuts. A table and culet were added and it gave gems more brilliance and fire. 1500-1600s. Came in many different shapes.
162
When were rose cuts popular and what were they good for
The rose cut appeared in the early sixteenth century and was popular until the nineteenth century. Unlike the table cut, it wasn’t designed for octahedral rough. Instead, it provided an efficient way to produce the largest possible gem from flattened rough.
163
What is the significance of the single cut?
Cutters of the mid-1600s introduced the single cut—or eight cut—based on the shape of octahedral rough. This simple style had more potential for brilliance than the table cut because it had more facets: a table, eight crown facets, eight pavilion facets, and sometimes a culet.
The single cut served as the basis for the full-cut modern brilliant.
164
what's an old mine cut and when were they popular?
a cushion shape with a high crown, deep pavilion, and large culet. The old-mine cut had the same number of facets—58—as the modern brilliant, but its pavilion was deeper, so it displayed less brilliance and fire. Still, the old-mine cut played an important part in the development of the modern brilliant cut. “Old-miners” became the most popular cut diamonds of the eighteenth century.
165
What's and old European Cut?
An early brilliant cut with a circular girdle.
166
What are the steps of diamond cutting?
Planning
Cleaving or sawing
Bruting
Polishing
A polished diamond must also pass a final inspection. This occurs after the diamond is boiled in a solution of hydrochloric and sulfuric acids to cleanse it of oil, diamond powder, and debris.
167
what does the planner do?
also called the marker—plays a vital role in diamond manufacturing. The planner decides where to mark the rough for cutting to produce the largest possible gem with the best clarity and proportions.
168
What is a kerf?
A notch scratched into diamond rough to prepare it for cleaving.
169
what is bruting?
A notch scratched into diamond rough to prepare it for cleaving.
170
what's a scaife?
A rapidly spinning horizontal disc coated with diamond powder, used to polish diamond rough.
171
What's a tang?
A device that holds the dop and allows polishers to adjust and maintain a diamond’s angle during polishing.
172
what is blocking?
Placing the first 17 or 18 facets on a diamond.
173
what did early cutters use to cut diamonds?
Early cutters used boards treated with diamond dust and olive oil to shape diamond rough
174
What are clarity characteristics?
Internal or external feature of a gemstone that helps determine its quality and establish its identity.
175
What is an inclusion?
Clarity characteristic totally enclosed in a polished gemstone or extending into it from the surface.
176
what is a blemish?
Clarity characteristic that’s confined to the surface of a polished gemstone.
177
WHen does a diamond receive a clarity grade?
Graders assign a diamond’s clarity grade after they find its clarity characteristics, identify them, and judge their visibility at 10X magnification.
178
What;s the purpose of clarity characteristics?
They determine a stone’s clarity grade. In the GIA system, the grade is based on the number, size, location, relief, and nature of a diamond’s characteristics.
They help determine a stone’s value. The presence or absence of clarity characteristics is a major diamond value factor.
They help identify a stone. Since no two diamonds have the same clarity characteristics in the same locations, you can use the characteristics to help tell one stone from another.
179
What is the first step in determining clarity?
For your first overall impression, look at the stone face-up through a fully corrected jeweler’s loupe or a binocular gemological microscope at 10X magnification. Then, with the same magnification device, inspect the stone more closely. Even after the follow-up inspection, however, your first look should strongly influence the gem’s clarity grade.
180
What's the correct loupe for grading?
Use only a triplet loupe that’s been fully corrected for color distortion, called chromatic aberration, and for linear distortion, called spherical aberration
181
What is dark field illumination and what is it used for?
Lighting of a diamond from the side against a black, non-reflective background. It makes inclusions stand out
182
what is a feather?
A trade term for any break in a diamond.
183
What is the wedge technique?
It divides the stone into eight sections—or wedges—so you can perform a systematic search for clarity characteristics. From the pavilion view, each wedge includes a pavilion main facet and two lower half facets, plus one-eighth of the girdle. From the crown view, the wedge includes two upper half facets, a bezel facet, half of two star facets, and one-eighth of the table.
184
what is a crystal inclusion?
A crystal (Xtl) is a mineral crystal contained in a diamond. Most often diamond, sometimes olivine, occasionally garnet
185
what's a needle inclusion?
A needle (Ndl) is a long, thin crystal that looks like a tiny rod at 10X magnification. A needle can appear white, bright, or dark
186
what's a pin point?
A pinpoint (Pp) is a very small crystal that looks like a tiny dot at 10X. Pinpoints are most often white, but they can occasionally be dark.
187
What's a cloud?
A cloud (Cld) consists of many tightly grouped pinpoints. The pinpoints might be too small to distinguish individually at 10X, but together they look like misty white or gray patches, or like tiny flecks of white powder.
188
What is a twinning wisp?
The twinning wisp (TW) is one of them. It’s a series of pinpoints, clouds, or crystals that forms in a twinned diamond’s growth plane. Twinning wisps appear flat and ribbon-like, and usually radiate out from the diamond’s center.
189
What's internal graining?
Internal graining (IG) is also caused by irregularities in crystal growth. Its appearance can take the form of lines, angles, or curves, and it might be whitish, colored, or reflective. It might give part or all of the stone a hazy texture and affect its transparency at 10X. It might also look like a thin sheet of reflective plastic inserted into the stone, or like fine white or colored streaks
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What is a grain center?
A grain center (GC) is a type of internal graining that consists of a small, concentrated area of crystal growth distortion. It can be white or dark, and it might have a thread-like or pinpoint-like appearance. Grain centers can look like transparent tornadoes caught deep inside the diamond. They can occur alone or in groups. They’re not visible from all directions, so they can disappear and reappear as you rock the diamond or move it from side to side.
191
What's a gletz?
A feather
192
What is break in any other direction that with cleavage called?
a fracture
193
what's an etch channel?
An etch channel (EC) is an angular opening that starts at the surface of the diamond and extends into it. It can be straight or curved, shallow or deep, and it often has striations perpendicular to its length. It is thought to occur when something etches, or chemically erodes, rough diamonds as they travel to the earth’s surface.
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what's a bearded girdle?
An etch channel (EC) is an angular opening that starts at the surface of the diamond and extends into it. It can be straight or curved, shallow or deep, and it often has striations perpendicular to its length. It is thought to occur when something etches, or chemically erodes, rough diamonds as they travel to the earth’s surface.
195
what's a bruise?
A bruise (Br) is a tiny area of impact accompanied by very small root-like feathers visible at 10X magnification. When viewed through an opposing facet, a bruise appears cottony in texture as it radiates into the diamond. A bruise is sometimes called a percussion mark.
196
What's a knot?
A bruise (Br) is a tiny area of impact accompanied by very small root-like feathers visible at 10X magnification. When viewed through an opposing facet, a bruise appears cottony in texture as it radiates into the diamond. A bruise is sometimes called a percussion mark.
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What is a patch?
A bruise (Br) is a tiny area of impact accompanied by very small root-like feathers visible at 10X magnification. When viewed through an opposing facet, a bruise appears cottony in texture as it radiates into the diamond. A bruise is sometimes called a percussion mark.
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What's a chip
A chip (Ch) is a shallow opening on the surface, located at the girdle edge, facet junction, or culet. It’s the result of damage that occurs after fashioning, so it won’t be accompanied by drag lines.
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What's a cavity?
A cavity (Cav) is an opening on the surface that occurs when part of a feather breaks away, or when a crystal drops out or is forced out, typically during polishing.
200
What's an indented natural
An indented natural (IN) is a portion of the original crystal surface, or skin, that dips below the polished diamond’s surface. The original surface might have growth markings such as trigons or parallel grooves.
201
What is fracture filling?
Treatment that involves injecting a molten glass substance into a diamond’s surface-reaching feathers or laser drill-holes.
202
What is flash effect?
A flash of changing color seen in a fracture-filled diamond when you look parallel to the filled inclusion and rock the diamond back and forth under magnification.
203
what are blemishes from?
Blemishes, or external clarity characteristics, can be caused by wear or the cutting process, or be a result of crystal structure. They all have one thing in common: They don’t appear to have depth when you view them at 10X magnification.
204
What's a nick?
A nick (Nck) is a small notch on a facet junction, usually along the girdle edge or at the culet. It’s smaller and shallower than a chip and has no readily apparent depth at 10X.
205
What's an abrasion?
A nick (Nck) is a small notch on a facet junction, usually along the girdle edge or at the culet. It’s smaller and shallower than a chip and has no readily apparent depth at 10X.
206
What's a scratch?
A scratch (Scr) is a thin, dull, white line across the diamond’s surface. It can be either curved or straight.
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where are extra facets usually located
the girdle
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what is lizard skin?
Lizard skin (LS) is a wavy or bumpy area on the surface of a polished diamond. It occurs when the cutter polishes too close to the octahedral plane or parallel to it.
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What are polish lines?
Polishing sometimes leaves fine, tiny, parallel grooves and ridges called polish lines (PL). They can occur on any facet, but they don’t cross facet junctions. Polish lines on adjacent facets run in different directions on diamonds. They’re transparent or white and can vary from heavy to faint. Although they’re on the surface, polish lines are usually easier to see if you look for them through the stone from the opposite side.
210
what's a burn?
Burn (Brn) is a hazy surface area that results from excessive heat applied during polishing, or occasionally from a jeweler’s torch. A surface burn caused by excessive heat at the location where the dop touches the diamond is referred to more specifically as a dop burn (Dop).
211
What's a pit?
A pit (Pit) is a small opening that usually looks like a tiny white dot. Pits usually result when pinpoint inclusions are pulled from the diamond during the polishing process.
212
what's a laser manufacturing remnant?
A laser manufacturing remnant (LMR) is a characteristic created during a laser manufacturing process, usually marking or sawing, that remains on the surface of a finished diamond. When it appears as a surface groove and shows no depth at 10X, it’s considered a blemish. Sometimes, the laser penetrates into the diamond, causing an internal or surface-reaching fracture. The fracture is considered an inclusion.
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What's a natural?
A natural (N) is a portion of the rough diamond’s original surface, or skin, that remains on a fashioned stone. Because a natural is a remnant of the original crystal, it sometimes shows growth marks, and it often has an uneven surface. When a cutter leaves a natural in place to save weight, it’s considered a sign of efficient cutting.
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What's surface graining?
Surface graining (SG) consists of one or more transparent lines on the surface of a finished diamond. It’s a visible indication of irregularities in the diamond’s crystal structure. Surface graining is related to internal graining and might appear in association with it.
Where grain lines exist, the polish might be better on one side of a grain line than on the other. Unlike polish lines, surface graining might change direction within a facet, might cross facet junctions, or it might run in a direction different from polish lines. Surface graining is almost impossible to remove because it’s part of a diamond’s distorted crystal structure.
215
What are the 5 factors that influence clarity grade?
```
Size
Number
Location (position)
Relief
Nature
```
216
What is relief?
is the contrast between an inclusion and its host gem. Relief can vary from high, or more apparent, to low, or less apparent. Generally, the more an inclusion differs in brightness, darkness, or color from its host, the more visible it is and the greater its impact on the clarity grade.
217
what is nature in relation to clarity grading?
Nature refers to the type of characteristic and its effect on the diamond. Inclusions have more impact on clarity than blemishes. Graders must sometimes refine the clarity grade to a higher or lower level because of nature.
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What are grade setting characteristics?
Inclusions or blemishes that establish the clarity grade of a diamond.
219
What features can a flawless diamond have and still be flawless?
A diamond can have these features, visible at 10X, and still qualify as Flawless:
Extra facets not visible face-up at 10X
Naturals entirely confined to the girdle as long as they don’t thicken the girdle or distort its outline
Internal graining that’s not reflective, white, or colored, and that doesn’t significantly affect transparency
Inscriptions that aren’t internal and don’t appear to penetrate the surface when viewed at 10X
Mounting features
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What is internally flawless?
An IF diamond shows only insignificant blemishes—no inclusions—when examined under 10X magnification.
221
What is VVS?
VVS diamonds contain minute inclusions that are difficult to see under 10X magnification. The inclusions in a VVS1 diamond are extremely difficult to see in the face-up position, or they might be visible only through the pavilion. In VVS2, they’re very difficult to see. (The GIA system uses words like “extremely” and “very” to describe subtle differences in difficulty or ease of viewing inclusions.)
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What is VS?
VS stones contain minor inclusions that range from difficult (VS1) to somewhat easy (VS2) to see under 10X magnification. All types of inclusions are possible. The grade depends on their overall visibility when considering all five clarity factors. Typical inclusions that might set the grade include small crystals, knots, distinct clouds, or minor surface-reaching inclusions such as feathers, cavities, or indented naturals.
223
What is SI?
SI stones contain noticeable inclusions that are easy (SI1) or very easy (SI2) to see under 10X. All types of inclusions are possible. The grade depends on their overall visibility when considering all five clarity factors. Typical inclusions that might set the grade include crystals, feathers, clouds, and twinning wisps.
As is the case with the VS range, a stone with an eye-visible inclusion can be graded SI, but in general the characteristics in an SI1 diamond are not usually visible face-up without magnification. You’ll see eye-visible inclusions more often in an SI2 stone.
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What is an I?
Diamonds in the I range contain inclusions that are obvious under 10X magnification. One or more of the following is typical of these inclusions:
They can be seen face-up without magnification
They seriously affect the stone’s durability
They’re numerous or large enough to affect transparency and brightness
The inclusions in I1 diamonds are usually quite visible to the unaided eye. In I2, they are easily visible. In I3, they are extremely easy to see and might affect the stone’s durability. Often, rough at this clarity level is used for industrial purposes. It’s faceted only if the current market demands it.
225
What's a plot?
A map of a diamond’s inclusions, blemishes, and facet arrangement.
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What does green ink mean?
Green ink indicates blemishes, with the exception of extra facets
227
What does red ink mean?
Red ink indicates most inclusions, even those that reach the surface
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what does red and green ink mean?
Red and green inks, used together, indicate cavities, indented naturals, knots, etch channels, and laser drill-holes
229
What does black ink mean?
Black ink indicates extra facets and, if the stone is mounted, the position of the metalwork
230
Are all characteristics plotted?
Not all characteristics are plotted. In fact, some grade- setting characteristics aren’t plotted at all, even on a laboratory report. Many diamond professionals plot only the characteristics that identify the stone, that set the grade, or that are important in establishing the diamond’s condition. The last is especially important in an appraisal. Some characteristics that aren’t plotted might be mentioned in a report’s comments section.
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What is the normal color range?
Range of diamond colors from colorless to light yellow, brown, and gray, also called the D-to-Z range.
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define colored diamonds?
Yellow, brown, and gray diamonds with more color than the Z master-stone, or that exhibit any other color face-up.
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what is hue?
Hue is the basic impression of a color, the component that gives color its family identity—the “reds,” the “blues,” the “greens.” White, gray, and black aren’t hues because they have no location in the color spectrum
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What is tone?
Tone is the relative amount of lightness or darkness in a color.
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What is saturation?
Saturation is the strength, purity, or intensity of the hue
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what is selective absorption?
Process by which a material absorbs some wavelengths of light and transmits others.
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What conditions influence color?
Two conditions influence the way a diamond absorbs light and, in turn, determine its color. One is the presence of impurities, or atoms other than carbon. The other is the presence of structural defects like missing carbon atoms or distortions in the crystal lattice.
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What are color centers?
Structural defect that influences an object’s absorption of light and can cause its color.
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What kind of diamonds are IA
All Type I diamonds contain nitrogen. Nitrogen is fairly plentiful in Type Ia diamonds, and its atoms are arranged in pairs or clusters. About 95 percent of cuttable-size natural diamonds are near-colorless to yellow Type Ia diamonds
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What are IB diamonds?
Type Ib diamonds are rare. They represent only one percent of all nitrogen-colored diamonds. They have fewer nitrogen atoms than Ia diamonds, and the atoms are scattered and isolated. Because of the arrangement of the nitrogen atoms, Type Ib diamonds usually have a more saturated yellow color.
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What are IIA diamonds?
Type II diamonds contain very little or no nitrogen, and they’re very rare. Type IIa diamonds are excellent conductors of heat. Most of them are colorless, but crystal distortion can make them brown or gray. The majority of the world’s most famous colorless diamonds are Type IIa, including the Cullinan, a colorless gem that weighed 3,106 cts. in its rough form.
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What are !!B diamonds?
Type IIb diamonds contain boron, which turns them blue and makes them excellent conductors of electricity. One of the most famous Type IIb diamonds is the 45.52-ct. Hope diamond.
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What is fluorescence?
Emission of visible light by a material when it’s exposed to ultraviolet radiation.
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What color do diamonds fluoresce?
Mostly blue, but can be any color
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Does fluorescence affect face down color?
no
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Does fluorescence improve face up color
yes
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How do size and shape affect color?
Size and shape are two aspects of cut that can influence diamond color. The larger a diamond is, or the deeper its pavilion, the farther light can travel in it. This increases the amount of selective absorption that takes place and often leads to a richer, more intense color.
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What is the most valued diamond color?
Diamonds with reddish colors are extremely rare and highly valued. They range from delicate pinks to reddish purples, and include pink-purples, orangy reds, purplish reds, and more.
Pure pinks are more popular than diamonds that are purplish, orangy, brownish, or grayish. Some trade professionals market very attractive stones in this category as “rose-colored,” and some stones with purplish tints as “mauve” diamonds.
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what causes pink diamonds?
Diamonds with reddish colors are extremely rare and highly valued. They range from delicate pinks to reddish purples, and include pink-purples, orangy reds, purplish reds, and more.
Pure pinks are more popular than diamonds that are purplish, orangy, brownish, or grayish. Some trade professionals market very attractive stones in this category as “rose-colored,” and some stones with purplish tints as “mauve” diamonds.
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what is the rarest diamond color
orange with no brown. Orange diamonds are so rare that scientists aren’t exactly sure what causes their extraordinary color. But it’s most likely the result of a combination of chemical impurities and structural distortion.
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what is the color of green diamonds usually like?
Green diamonds are typically light in tone and low in saturation. Their color often appears muted, with a grayish or brownish cast. The hue is generally in the yellowish green category. The hue is confined mostly to the surface, and rarely extends through the entire stone. That’s why cutters try to leave as much of the natural rough around the girdle as possible.
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what causes green color in diamonds?
Most green diamonds get their color when radiation displaces atoms from their normal positions in the crystal lattice. This can happen naturally when diamond deposits lie near radioactive rocks, or as a result of treatment by irradiation.
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what are chameleon diamonds?
A very few green diamonds are called “chameleon diamonds.” Their color is caused by hydrogen impurities. Ordinarily, they’re a grayish green color. But their color changes dramatically to bright yellow when they’re heated over a flame or left in the dark for at least 24 hours. The yellow color lasts for a few minutes after the heat is removed or the diamond is once more exposed to light, then it returns to its stable grayish green.
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what makes the Dresden Green special?
The distribution of the green color throughout this diamond is what makes it so rare. While most green diamonds get their hue from green “skins” that are mostly removed during the cutting process, the Dresden Green is a beautiful, bottle-green hue throughout. The rare, uniform green hue is actually caused by exposure to radiation over a long geological time span.
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What causes brown color in diamonds?
Internal parallel grain lines cause the brown color in diamonds. If the brown grain lines exist in a diamond that’s also colored yellow by nitrogen impurities, they produce a brownish yellow color.
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what are masterstones?
A set of color-comparison diamonds that defines GIA diamond color grades in the normal (D-to-Z) range.
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what direction are diamonds graded?
Table down, face down
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Whatt environment should color be graded in?
The first requirement for color-grading diamonds is a white or neutral surface with a matte finish. Jewelry professionals who have to color-grade at trade shows or in retail stores can use white, non-fluorescent, plastic grading trays or folding, pocket-sized cards. Sometimes, they also fashion disposable trays from white business or index cards. Most gemologists use a DiamondDock
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What kind of light is required for diamond grading?
The most widely available and accepted lighting for color-grading diamonds is balanced, daylight-equivalent, fluorescent light. The overhead light on many gemological microscopes provides this kind of light.
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What is the master eye effect?
The optical illusion that causes the ungraded diamond to appear either lighter or darker than the masterstone, depending on which side it’s on.
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Why do you grade color before fluorescence?
Although it’s rare, some diamonds will change color temporarily when exposed to UV radiation. Therefore, it’s important for the grader to evaluate color before determining fluorescence.
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What are the terms GIA uses to describe colored diamonds?
GIA uses the following grade terms to describe the combined effect of tone and saturation on the diamond’s hue:
```
Faint
Very Light
Light
Fancy Light
Fancy
Fancy Intense
Fancy Dark
Fancy Deep
Fancy Vivid
```
To complete the description, one of these terms is followed by the name of the diamond’s hue. The entire description is then recorded on the colored diamond report. These tone and saturation terms play a significant role in determining colored diamond value: The stronger the hue, the more valuable the diamond.
263
Are all colored diamonds graded in the same boundaries of saturation and tone?
No. The system is designed to accommodate the fact that not all colored diamonds have the same depth of color. For example, yellow diamonds occur in a wide range of saturations while blue diamonds do not. For that reason, the boundaries for fancy grades in the yellow hue range allow for greater depths of color than they do in the blue hue range.
264
what is characteristic color?
The basic face-up color of a colored diamond.
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what direction are colored diamond graded
face up
266
What affects GIA cut grade?
A GIA cut grade is influenced mostly by the diamond’s proportions. If one proportion factor is more extreme than the others, it can lower the cut grade of an otherwise well-cut diamond. An extremely large table facet, a very steep crown, a very deep pavilion, or a thick girdle can reduce a diamond’s cut grade significantly.
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What is the average girdle diameter?
The result achieved by adding the smallest and largest diameter measurements of a round brilliant and dividing by two.
268
what is total depth percentage?
Table-to-culet depth, expressed as a percentage of average girdle diameter.
269
how do you figure out total depth percentage?
divide depth by diameter
270
what is generally a good depth percentage?
60%
271
what is table percentage?
A diamond’s table size expressed as a percentage of its average girdle diameter.
272
what table sizes negatively affect diamonds?
Despite these market preferences, a table that is very small (below 50 percent) or very large (above 70 percent) tends to have a negative effect on a diamond’s face-up appearance and cut grade.
273
How do you measure a table?
Take four measurements corner to corner. Add them then divide by 4. Then divide table measurement by girdle diameter and multiply by 100
274
what do you measure the table with
table gauge
275
what are the 3 table percentage estimation methods?
flash, ratio, and bowing
276
what is the flash method?
With your unaided eye, look at the diamond in the face-up position and rock it back and forth under an overhead light source. The flash of white you see is the light reflecting off the table. Your perception of the size of this flash determines your estimate of the table percentage.
277
What is the ratio method
draw a line with your eye from girdle through culet (through star facet) and compare inner and outside length
278
what is the bowing method?
o estimate table size using the bowing method, look at the stone face-up under magnification with overhead lighting. Identify the line that begins at the point of one star facet, and travels along the table edge to the point of the next star facet. Four of these lines form the outline of a box.
If they bow in noticeably, table percentage is about 53 percent
If they bow in slightly, table percentage is about 58 percent
If they don’t bow at all—if the lines are straight—table percentage is about 60 percent
If they bow out slightly, table percentage is about 63 percent
If they bow out noticeably, table percentage is about 67 percent
279
How do you measure star length percentage?
Examine all eight star facets as you work your way clockwise around the gem. Using the distance between the edge of the table facet and the girdle as 100 percent, estimate the distance each star facet reaches toward the girdle. One-third of the way is equivalent to approximately 35 percent. Halfway corresponds to a 50 percent star length percentage. Two-thirds corresponds to approximately 65 percent. Three-quarters of the way toward the girdle edge corresponds to a star length percentage of 75 percent.
Once you have estimates for all eight star facets, average them and round that figure to the nearest 5 percent. Star length percentages typically range from 50 percent to 55 percent
280
what is crown angle?
The angle formed by the bezel facets and the girdle plane.
281
What is crown height percentage?
The distance from the girdle plane to the table, expressed as a percentage of average girdle diameter.
282
What is the best crown angle?
Generally, crown angles from about 25° to about 35° produce attractive, bright, and fiery diamonds if other proportions are compatible.
283
How do you estimate crown angle?
To estimate the crown angle using the profile method, hold the diamond table-to-culet and look at it under magnification with overhead or darkfield light.
First, examine the angle between each bezel facet and the table plane. Make sure you’re looking at bezel facets and not the star and upper half facets. In profile, the bezel facet has a flat plane. The star and upper half facets don’t form a single flat plane.
Focus on each of the eight bezel facets, estimate their angles, and mentally arrive at an average. Remember that a right angle is 90 degrees, half a right angle is 45 degrees, and one-third is 30 degrees. Use these angles as references. This procedure might be easier than you think: The human eye is actually quite sensitive to slight differences in angles.
284
What's the face up method of estimating crown angle?
look at it under magnification with darkfield lighting. Look through the table and locate one of the pavilion main facets.
Mentally divide the pavilion main into two parts: one that runs from the culet to the corner where the table meets the bezel facet, and one that runs through the bezel facet to the girdle edge. Compare its width where it meets the table corner to its width at the top point of the bezel facet. The greater the difference between the two widths, the steeper the crown angle.
With a 25° crown angle, the width of the pavilion main appears the same in both sections.
With a 30° crown angle, the pavilion main appears slightly wider at the bezel facet.
With a 34.5° crown angle, the pavilion main looks nearly twice as wide at the bezel facet.
With a 39° crown angle, the pavilion main looks more than twice as wide at the bezel facet.
With a very steep crown angle—40° and beyond—you can see the entire image of the pavilion main, and sometimes even the culet.
285
Where do you measure girdle thickness?
In the valleys
286
what is painting?
A weight-retention method that adjusts the angles of some facets to allow portions of a diamond’s girdle to be thicker.
287
what is digging out?
A weight-retention method where the cutter leaves more girdle thickness to allow for later removal of clarity characteristics around the girdle.
288
What can significant painting cause?
Significant painting might cause large areas of the diamond to flash all at once, changing the balance of the diamond’s face-up pattern.
289
What can significant digging out cause?
Digging out might produce dark upper half facets and make the stone look dark face-up. It also makes the gem look smaller because the diamond’s brightness doesn’t extend to the girdle edge.
Severe digging out might make some crown facet junctions appear less sharp, to the point where adjacent upper half facets look like a single large facet. This significantly alters the diamond’s pattern by causing larger areas of the diamond to flash at the same time.
290
How do you figure out crown height percentage?
CHart. You have to have the table percentage and crown angle.
291
What is finish?
The quality of the polish and precision of the cut of a fashioned gemstone.
292
what does the pavillion do?
A diamond’s pavilion facets take the light that enters from above and reflect it back toward the crown, giving the diamond its spectacular brightness. The pavilion is also designed to take advantage of diamond’s unique ability to break light up into its spectral colors and create fire.
293
what's pavillion depth percentage?
The distance from the girdle plane to the culet, expressed as a percentage of average girdle diameter.
294
What's the pavillion angle?
The angle formed by the pavilion mains and the girdle plane.
295
what's the relationship between pavilion depth percentage and angle?
Generally, the greater the pavilion depth percentage, the steeper the pavilion angle. This chart shows the relationship between these two parameters.
296
what can a too steep or shallow pavilion angle produce?
Steep pavilion angles produce dark areas under the diamond’s table. Shallow pavilion angles, in combination with large tables and shallow crown angles, might produce unattractive reflection effects like fisheyes. Increasing the pavilion angle too much causes light leakage and makes the center of the stone darker.
297
how do you figure out girdle thickness percentage?
To calculate girdle thickness percentage, you need to know the diamond’s total depth, crown height, and pavilion depth percentages. Simply subtract the crown height percentage and pavilion depth percentage from the total depth percentage, then round the final figure to the nearest 0.5 percent.
298
How do you figure out lower half length percentage?
Under 10X magnification, examine all eight pairs of lower half facets as you move clockwise around the gem. Consider the distance between the culet and the girdle as 100 percent. Estimate the distance each lower half facet reaches toward the culet. If it reaches halfway to the culet, the length is 50 percent; three-quarters of the way, it’s 75 percent; two-thirds of the way, it’s about 65 percent.
After you have estimates for all the lower half facets, average the results and round that figure to the nearest 5 percent.
If a diamond’s lower half length percentages differ noticeably, the stone is not symmetrical. In that case, the culet might also be off-center or the pavilion mains might appear to be different sizes or shapes.
299
what is design?
A diamond’s physical shape, including its proportions and durability, determined by decisions made during the fashioning process
300
what is craftsmanship
The care that goes into the fashioning of a polished diamond, as confirmed by its finish
301
what is overweight percentage
The difference between an overweight diamond’s suggested weight and its actual weight can be expressed as its “overweight percentage.” This percentage can have a negative effect on the diamond’s cut grade.
302
how do you evaluate symmetry
To evaluate symmetry, you consider the evenness of a diamond’s outline and the size, shape, and placement of its facets. Examine the diamond under 10X magnification and evaluate each symmetry aspect against an ideal of absolute perfection. A symmetry rating can range from excellent to poor.
303
what is the belly on a fancy cut stone?
The central area of the side of a pear, marquise, heart, or oval, where it curves out slightly, is called the belly
304
What is the area between the belly and the point on a fancy cut called?
The wing
305
What is the rounded end of a pear called?
Head
306
What is the curved area between the belly and the head of a pear called?
the shoulders
307
What are french tips and why do they use them
A faceting style that replaces the large bezel facets at the points of marquises, pears, and hearts with star and upper half facets. It prevents breakage
308
what is the bottom part of a fancy cut called where the pavilion facets come together?
keel line
309
How do you compare a fancy cut to a master stone?
hold it face down at a 45 degree angle
310
Are large tables over 80% common in fancy cuts?
yes
311
What dimension do graders use to measure the table of a fancy cut?
largest table size across width
312
How do graders estimate crown angle on a fancy?
They do this by looking lengthwise at the stone’s profile. For brilliants, graders examine the bezel facets at the belly.
313
What is the formula for total depth percentage for a fancy cut?
Stone depth ÷ stone width × 100 = total depth percentage
314
how do graders evaluate pavilion depth in fancy cuts?
The first thing graders do is look at stones face-up to see if they’re reasonably brilliant. Appearance can indicate whether the pavilion is deep or shallow. If a diamond is glassy or watery looking, or if the girdle’s reflection is visible at the sides of the table, the pavilion is probably shallow; if the stone looks dark, it’s probably deep.
Next, graders evaluate pavilion depth by looking at the stone in profile and visually comparing the crown height to the pavilion depth. To be well proportioned, a gem’s pavilion should be about 2.5 to 4.5 times the depth of its crown.
315
how do you calculate lenth to width ratio?
Here’s an example:
For an oval with a length of 9.00 mm and a width of 6.00 mm:
9.00 ÷ 6.00 = 1.50
The length-to-width ratio for that stone is 1.50:1.
316
What's a potential?
Diamonds that can be repolished to improve their clarity to an Internally Flawless grade.
317
What's an improvable?
Diamonds that can be repolished to improve their clarity to a VVS1 or VVS2 grade.
318
Why are stones recut?
Most stones are recut to improve their brightness and their balance between brightness and fire. The recut often makes the stone more attractive, but unless it can be done with a minimum loss of weight and apparent size, it might not be worth doing.
319
What's the main consideration when considering whether to recut a diamond?
In the trade, the difference between the original value and the recut value will always be the primary consideration. But this isn’t always the case with consumers. A diamond’s value and its appearance carry different importance for different people. An individual might have damaged a diamond with sentimental value and want to maintain its appearance as much as possible, even if it means a loss of weight
320
when are fancy cuts recut
when they're broken
321
what is a simulant?
Any material that is not diamond or synthetic diamond, but which imitates a diamond’s appearance and is used in its place.
322
what is making a separation?
Process of distinguishing natural minerals and gems from each other as well as from synthetics, simulants, and treated gems.
323
what is strass or paste?
Glass has been an effective diamond imitation since the 1700s, when European glassmakers discovered that adding lead oxide to glass made it much more dispersive and brilliant. The process resulted in a convincing diamond simulant, just when diamonds began to gain popularity
324
what did Rhinestone first refer to?
The word originally referred to simulants made from a colorless quartz from the Rhine River Valley.
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What is synthetic spinel used for?
Synthetic spinel is inexpensive to produce, and you’ll still find it in class rings and imitation birthstone jewelry.
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who invented the flame fusion process of synthetic crystal growth and when?
French chemist Auguste Verneuil in the late 1800s
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what were the first gems synthesized with flame fusion?
rubies and sapphires
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What are characteristics of rutile as a simulant?
As a simulant, synthetic rutile is quite brilliant, but not as brilliant as diamond. It also has very high dispersion: Even to the untrained eye, its rainbow colors are obvious. They’re so obvious that they actually detract from its brilliance. Another serious drawback to its use as a simulant is its low hardness—it quickly shows signs of wear. Doubly refractive
329
What are characteristics of strontium titanate as a simulant
Strontium titanate (a compound of the elements strontium and titanium) first appeared as a simulant in 1953. It had no known natural counterpart until scientists identified the mineral tausonite in the 1980s. Like diamond, it’s singly refractive. It’s closer to colorless and much less dispersive than synthetic rutile, but still noticeably more dispersive than diamond. It has low hardness, so it’s not very durable.
330
why was yttrium aluminum garnet popular?
Because it has relatively good hardness (about 8¼ on the Mohs scale) and brilliance, YAG was the most popular diamond simulant for many years. But still, it lacked the distinct fire of diamond. As newer and better simulants appeared, YAG lost its popularity.
331
What were the benefits and drawbacks of gadolinium gallium garnet?
GGG, was the next garnet-like material to be used as a diamond simulant. It’s a little more brilliant and dispersive than YAG. In fact, its dispersion is almost the same as diamond’s, so it shows similar fire. GGG’s major drawback is its lower hardness: It scratches fairly easily. It also has high SG, so it’s much heavier than a diamond of the same size.
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What is synthetic moissanite made of?
silicon carbide with a natural counterpart that occurs as tiny grains in rocks and meteorites. (It can also occur as inclusions in natural diamonds, but this is rare.
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Can moissanite fool a thermal tester?
Yes
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what is HPHT?
Diamond synthesis method that mimics the pressure and temperature conditions that lead to natural diamond formation.
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when were the first lab grown diamonds created and what were they used for?
Early 1950's by GE. Used for industrial purposes.
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when was the first cuttable lab created diamond created
1970
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what is flux?
A flux is a solid material that, when melted, dissolves other materials.
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what is chemical vapor deposition
An industrial process adapted to allow growth of synthetic diamond from carbon-rich gas in thin layers onto a silicon or diamond surface.
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what are some ways to differentiate lab grown diamonds from mined?
Examining the diamond with a microscope, looking for inclusions, color zoning, and graining
Checking the diamond’s fluorescence under ultraviolet (UV) radiation
Checking the diamond’s reaction to a magnet
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what kind of inclusions are in lab grown diamonds
metallic flux from growing
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what kind of inclusions to CVD diamonds get
small, opaque, irregular inclusions that are thought to be particles of non-diamond carbon. Also brown graining
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what is irradiation?
Exposure of a material to radiation; causes color change in diamonds.
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Can the heat from repairs change the color of irradiated diamonds?
yes
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What does annealing do in irradiation?
A controlled heating and cooling process called annealing, which you read about in Assignment 12, is another way to change diamond color. When it follows irradiation in a two-step process, annealing modifies irradiated colors to produce brown, orange, or yellow. Rarely, it can also produce shades of pink, red, or purple.
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What can HPHT do to change the color of diamonds?
Depending on the starting material, this treatment can improve the color of brownish Type IIa and some very rare Type Ia diamonds, making them almost colorless. It can also create green or yellowish green diamonds from another category of brown Type Ia diamonds.
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what are coated diamonds?
These modern silica coatings are applied to polished colorless or near-colorless diamonds. The process results in a variety of natural-looking fancy colors, including pinks, oranges, yellows, blues, and violets.
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what's a diamontaire?
A knowledgeable, experienced, and successful person, usually a dealer or manufacturer, in the diamond trade.
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what is a lot price?
A discounted price for buying an entire parcel, or a substantial part of it.
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what is pick price?
A premium price for selecting stones from a parcel.
350
When were diamonds that exist today delivered to the surface?
2.5-20 billion years ago
