Chapter 7 Key Concepts & Terms

Question 1

What is the relationship between the angle of incidence and the angle of reflection?

Answer 1

They are always equal.

Question 2

What is the refractive index (RI) of air assumed to be in gemology?

Answer 2

1.

Question 3

Do all gem materials have RIs higher than 1?

Answer 3

Yes.

Question 4

How does light travel in materials with higher optical density compared to lower optical density?

Answer 4

Light travels more slowly.

Question 5

When does refracted light bend toward the normal?

Answer 5

When traveling from a less refractive material to a more refractive material.

Question 6

When does refracted light bend away from the normal?

Answer 6

When traveling from a more refractive material to a less refractive material.

Question 7

What is the relationship between refractive index and critical angle?

Answer 7

Higher RIs have smaller critical angles.

Question 8

What is the critical angle of diamond?

Answer 8

24.5 degrees.

Question 9

How does diamond’s small critical angle affect light?

Answer 9

It limits the opportunity for light to exit the stone.

Question 10

What does dispersion measure in a material?

Answer 10

The RI difference between the violet and red light rays.

Question 11

Is dispersion an optical property that varies by material?

Answer 11

Yes.

Question 12

What happens to light absorption as it travels further in a gemstone?

Answer 12

More absorption occurs.

Question 13

What is diamond’s brightness related to?

Answer 13

The amount of light reflected back to the observer.

Question 14

What does a diamond’s face-up pattern reveal?

Answer 14

Nearly all of the cutter’s fashioning choices.

Question 15

What term do diamond professionals use to describe a diamond’s display of dispersion?

Answer 15

Fire.

Question 16

What is the best way to see a diamond’s fire?

Answer 16

Look at the stone face-up while rocking and tilting it.

Question 17

How does absorption affect the color of colored diamonds?

Answer 17

More absorption causes deeper color; less absorption causes lighter color.

Question 18

How can cutting alter a diamond’s color appearance?

Answer 18

By changing the length of the path of light in the diamond.

Question 19

What is the GIA Cut Grading System based on?

Answer 19

Both scientific research and observation.

Question 20

What does each cut grade in the GIA Cut Grading System include?

Answer 20

A range of proportion combinations and a variety of appearances.

Question 21

To what diamonds does the GIA Cut Grading System apply?

Answer 21

Round brilliant diamonds in all clarities across the D-to-Z color range.

Question 22

What is a combined evaluation in the GIA Cut Grading System based on?

Answer 22

Face-up appearance, design, and craftsmanship.

Question 23

What can affect a diamond’s appearance?

Answer 23

Variations in lighting and surroundings.

Question 24

What type of lighting helps evaluate a diamond’s brightness?

Answer 24

Diffused fluorescent lighting.

Question 25

What is Adamantine?

Answer 25

The highest degree of luster possible in a transparent material. ## Footnote Adamantine is often associated with diamonds and other gemstones that exhibit exceptional brilliance.

Question 26

Define the angle of incidence.

Answer 26

The angle at which light hits a surface or boundary, measured between the normal and the incident light. ## Footnote This angle is crucial in understanding how light interacts with different surfaces.

Question 27

What is the angle of reflection?

Answer 27

The angle at which light returns from a surface or boundary, measured between the normal and the reflected light. ## Footnote The angle of reflection is equal to the angle of incidence.

Question 28

Define the angle of refraction.

Answer 28

The angle at which light bends when it travels from one material to another, measured between the refracted light ray and the normal. ## Footnote This bending occurs due to a change in speed as light enters a different medium.

Question 29

What does brightness refer to in terms of diamonds?

Answer 29

The effect of all the diamond’s internal and external reflections of white light. ## Footnote Brightness contributes significantly to the overall visual appeal of a diamond.

Question 30

What is the critical angle?

Answer 30

The angle of incidence at which the angle of refraction reaches 90 degrees and total internal reflection begins to occur. ## Footnote This concept is important in understanding how light behaves in gemstones.

Question 31

Define dispersion.

Answer 31

The optical phenomenon of white light separating into spectral colors. ## Footnote Dispersion is responsible for the colorful flashes seen in gemstones.

Question 32

What does luster refer to?

Answer 32

The appearance of a material’s surface in reflected light. ## Footnote Luster can vary from dull to brilliant, affecting the gemstone's aesthetic.

Question 33

What is a normal in optics?

Answer 33

An imaginary line perpendicular to the surface of a boundary. ## Footnote The normal is used as a reference for measuring angles of incidence and reflection.

Question 34

Define optical density.

Answer 34

The ability of a medium or material to slow down the light that travels in it. ## Footnote Higher optical density results in a greater reduction in light speed.

Question 35

What is path length in terms of light?

Answer 35

The total distance a light ray travels in a gemstone. ## Footnote Path length affects the intensity and color of light that emerges from the gemstone.

Question 36

Define pattern in the context of gemstones.

Answer 36

The relative size, arrangement, and contrast of bright and dark areas when viewed face-up. ## Footnote A well-defined pattern enhances the visual appeal of a gem.

Question 37

What does polish refer to in gemstones?

Answer 37

The overall condition of the facet surfaces of a finished diamond. ## Footnote A good polish improves light reflection and overall appearance.

Question 38

What is reflection in optics?

Answer 38

The light returned when it hits a surface or a boundary between two different materials. ## Footnote Reflection is key to understanding how light behaves on gemstone surfaces.

Question 39

Define refraction.

Answer 39

The change in speed and possible change in direction of light as it travels from one material to another. ## Footnote Refraction is a fundamental principle in optics, impacting how we perceive gemstones.

Question 40

What is the refractive index?

Answer 40

A measure of the change in speed and direction as light travels from the air to a certain material. ## Footnote The refractive index is critical in characterizing gemstones.

Question 41

Define symmetry in gemstones.

Answer 41

The exactness of a finished gem’s shape and facet placement. ## Footnote High symmetry is often associated with higher quality in gemstones.

Question 42

What is total internal reflection?

Answer 42

Complete reflection of a light ray within a material. ## Footnote This phenomenon is essential for the brilliance seen in diamonds.