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level: Colour Filters and colour change effects

Questions and Answers List

level questions: Colour Filters and colour change effects

Question	Answer
Colour filters can be used to analyse what aspect of a gemstone?	The body colour
Filter tests can be used to help quicly distinguish...	Similar looking gemstones
What is the name of the most common colour filter used that transmits deep red and yelow-green light?	Chelsea colour filter
What colour should an emerald show as when viewed through the Chelsea colour filter?	Red
What colour do stones with cobalt componds, such as blue synthetic spinel and glass, show as through the Chelsea colour filter?	Red or pink
The colour-change effect in gemstones is caused by viewing the gemstones in different intensities of...	White light
What two colours are seen in different lights for the stone alexandrite?	Red and green
What is the term used to describe gem materials with a crystalline structure that absorb lightwaves differently within different vibration directions?	Pleochroism
Pleochroic gem materials show completely different colours when viewed from different..	Directions
What is the term used to describe the effect produced by uniaxial materials where the two principal vibration directions are differentially absorbed, producing two different colours?	Dichroism
What is the term used to describe the effect produced by biaxial materials where the three principal vibration directions are differentially absorbed, producing three different colours?	Trichroic
What is the name of the too used to see pleochroism in gem materials that is otherwise undetectable to the naked eye?	Dichroscope
Positive detection of pleochroism in gem materials can help distinguish _________ materials from ___________ materials in stones that look otherwise similar to the naked eye.	Isotropic
The London dichroscope is made up of two polarizing filters placed next to eachother at...	90 degrees to one another
When using the dichroscope, what must with you do with the gem material in order to line up the crystal structure orientation with the polarizing filters?	Turn it
What type of gemstones cannot be tested using the dichroscope?	Opaque
What needs to be used alongside the dichroscope in order to get an accurate reading?	White light
What types of gem materials cannot display pleochroism?	Cubic and amorphous
Pleochroism can only be observed in ________ stones.	Coloured
Pleochroism is not seen in all optically ___________ coloured gem materials.	Anisotropic
Pleochroisim does not occur along what, meaning it is essential to turn the stone during testing?	Optic axis
What pleochroic colours are seen in blue sapphire?	Blue and green
What pleochroic colours are often seen in tanzanite?	Blue, violet and yellow
What pleochroic colours are seen in aquamarine?	Blue and colourless
What pleochroic colours are seen in ruby?	Red and orange