Colour Flashcards
(28 cards)
What is white light?
A combination of all the colours in the range of visible light energy. It is made up of a continuous band of wavelengths
What is the visible spectrum?
The whole range of colours and wavelengths
What is the range of visible light wavelengths in nm?
400nm to 700nm
How is colour produced in gems?
During modification of white light, as a result of selective absorption, dispersion and diffraction
What does idiochromatic mean?
Gem materials where the colouring element forms an essential part of the atomic structureand are said to be ‘self coloured’
What does Allochromatic mean?
Gem materials where the colouring elements are not essential but are present as an impurity, are ‘other coloured’
What colour do the following elements produce?
- Titanium
- Vanadium
- Chromium
- Manganese
- Iron
- Cobalt
- Nickel
- Copper
- Titanium - BLUE
- Vanadium - GREEN/PINK
- Chromium RED/GREEN
- Manganese - PINK
- Iron - GREEN/BLUE/RED/YELLOW
- Cobalt - BLUE
- Nickel - GREEN
- Copper - GREEN/BLUE
What elements produce colour in diamonds?
Boron and nitrogen
Why does the same element produce different colours in different gem materials?
Due to the environment and relationship to oxygen in the crystal lattice the energy levels of electrons will differ causing the the brain to influence the colours differently.
Explain selective absorption of light in relation to body colour of gem stones
Coloured gems remove (absorb) some wavelengths from white light. The remaining energy is transmitted to brain as residual light which is then interpreted as a single colour - body colour
What does the spectroscope do?
It detects the wavelengths in the spectrum where absorption occurs. It splits the light into its constituent wavelengths using an optical device called diffraction grating.
What is dispersion?
The splitting of white light into the spectral colours when it passes through two inclined surfaces of a transparent material. It occurs because each colour is refracted as at a different angle. The amount of dispersion in a gemstone is the difference in refractive index measured in red and blue light
What colour is refracted the most?
Violet
What colour is refracted the least?
Red
What are the dispersion values of Diamonds, CZs and Synthetic Moissanite?
Diamond - 0.044
CZ - 0.065
Synthetic Moissanite - 0.104
What is diffraction?
When light passes through a minute slit or hole they become slightly spread out (diffracted). If white light is passed through a very fine grid of parallel line imprinted on a transparent sheet, the diffracted waves produce a spread out spectra. This is called DIFFRACTION GRATING
How is colour effect in opals produced?
Interference of light is diffracted through gaps between minute spheres in the opal structure.
Why do emission lines occur in the spectrum?
Result of fluorescence and occurs when shorter wavelength energy is converted into longer wavelength light.
What light should NOT be used when using a spectroscope?
LED torch
Fluorescent lamp
Daylight
What is the Chelsea Colour Filter?
It is a colour filter that transmits only deep red and yellow/green light. originally desgined to distinguish between natural and simulant emeralds. however no longer used for this purpose. However they can help distinguish between other similar looking stones
Explain the Colour Change Effect
Different white light sources produce different combinations of wavelengths. Gemstones can be different colours in different types of incident white light.. EG Alexandrite is red under tungsten light and green in daylight.
What is Pleochroism?
It is a body colour effect possessed by many optically anisotropic coloured gemstones. Pleochroic materials selectively absorb light waves differently in different vibration directions. A different body colour is transmitted by each vibration direction.
Which stones display DICHROISM?
Uniaxial materials (tetragonal, trigonal and hexagonal). they have two principle vibration directions which produce a two coloured effect called dichroism.
Which stones display TRICHROISM?
Biaxial materials (orthorhombic, monoclinic and triclinic). They have three principle vibration directions which exhibit three colours.
