GEM ID Flashcards
GEM ID (28 cards)
What is the Angle of incidence?
The angle at which a ray of light strikes a surface, measured from the normal.
What is the angle of refraction?
The angle between the normal and a refracted light ray.
What is Biaxial?
Doubly Double refractive with two optics axies.
Birefringence is..
The numerical difference between a DR gem’s highest and lowest RIs.
What is birefringence blink?
A method of determining birefringence that involves looking for a light-to-dark or green-to-red change in a spot.
What is contact liquid?
Liquid that makes an optical contact between a refractometer hemicylinder and the material being tested.
What is the critical angle?
An angle between the normal and the maximum angle of refraction.
Explain doubling.
The appearance of double images of a gemstones features on the side opposite the viewer.
Explain doubly refractive
Possessing different physical or optical properties in different crystal directions.
What is Anisotropic?
It means double refractive
What is an Extraordinary Ray?
The polarized ray that transmits through uniaxial stone with a varying RI
What is a Hemicylinder?
A half cylinder in a refractometer, made of high lead, high -RI glass, on which a gem is placed.
Explain monochromatic light
light that consists of only one wavelength and one hue.
What is the ‘normal’
An imaginary line perpendicular to the point where a ray of light strikes the surface.
What is an oblique angle?
Any line other than a right angle.
What is an optic axis?
Direction of single refraction in a double refractive gem.
What does ‘Optic character’ mean?
The number of optic axes in a doubly refractive stone.
What is an ‘Optic Sign’?
Statement of the relationship between the Dr stones’ two RI’s.
What is an ordinary ray?
The Polarised ray that transmits through a uniaxial stone with an RI that remains constant.
What is OTL?
Description of a gem with an RI higher than that of the contact liquid.
What is a Parallax?
Wavering of RI reading between scale divisions.
Explain Polarization.
Limiting a light beam to one vibration plane that’s perpendicular to it direction of travel.
Refraction is…
The change in speed and possible bending of light as it passes through one material to another.
Refractive index is….
A measure of the change in the speed and angle of light as it passes from one material to another.
