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level: Observations and Tests using Optical Properties

Questions and Answers List

level questions: Observations and Tests using Optical Properties

Question	Answer
What is the optical effect created by light reflecting off of multiple long, parallel inclusions at a right angle?	Chatoyancy
What is the optical effect created by light reflecting off of multiple long inclusions in two or more directions?	Asterism
What cut is best to show off the asterism and chatoyancy effect in gemstones?	Cabochon
What is the term used to describe the return of light due to reflection in a faceted gemstone when viewed face up?	Brilliance
The proportions of what factor in relation to a gemstone ensures maximum return or light, therefore maximum brilliance?	Cut
In a well proportioned brilliant cut diamond, what effect causes a high degree of brilliance to be shown by way of light entering the stone, then being returned back?	Total Internal Reflection
What is the name of the tool that can be used to test whether a gem is isotropic, anisotropic or polycrystalline using two polarizing filters?	Polariscope
If a stone is rotated 360 degrees on a polariscope and remains dark (letting no light through), what type of stone would it be?	Isotropic
If a stone is rotated 360 degrees on a polariscope and goes dark and light 4 times, what type of stone would it be?	Anisotropic
If a stone is rotated 360 degrees on a polariscope and remains light (letting light through), what type of stone would it be?	Polycrystalline
What is the name of the effect seen through a polariscope which shows strains/bands of darkness in various orientations in an otherwise light stone?	Anomalous Extinction
In what type of stone would you see anomalous extinction?	Isotropic
What causes an anomalous extinction effect to appear in gemstones?	Stress and Pressure
What is the name of the tool used to read the refractive index of a gemstone?	Refractometer
When testing a gemstone using a refractometer, the gem is placed on the ____________?	Glass Table
What is used when testing a gem using a refractometer to allow optical cointinuity?	High RI Fluid
What other item is used with a refractometer to be able to get a reading?	Monochromatic Light
If two shadow edges are seen on the refractometer scale, what does this indicate?	Double Refraction
If a dark scale with no clear shadow edge is seen on the refractometer scale, what could this be an indication of?	Gemstone RI too high
When testing a stone on the refractometer with double refraction, what should you do to see if a stone is uniaxial or biaxial?	Rotate 360 degrees
If only one shadow edge moves during a 360 degree rotation of a stone on the refractometer, what type of stone is it?	Uniaxial
If both shadow edge's moves during a 360 degree rotation of a stone on the refractometer, what type of stone is it?	Biaxial
What sort of gemtone should not be tested on a refractometer as it can cause damage to the glass table?	Diamond