GI-4: Polariscope Testing Flashcards
Airy’s Spiral
A uniaxial optic figure that resembles a pinwheel or a cross with curving arms, surrounded by rings
Analyzer
The polariscope’s upper polarizing filter, which can rotate
Anomalous Double Refraction (ADR)
A false indication of a double refraction in a material, caused by internal strain that occurs during formation
Brush
A shadowy line across an optic figure that’s wide at the ends and narrow in the center
Bull’s Eye
A uniaxial optic figure wth a central open area that resembles the center of a target. Only seen in Quartz.
Crossed Filters
The polaricope’s closed, or dark, position, with the light-transmitting directions of the analyzer and polarizer perpendicular to each other
Crosshatch
A pattern of intersecting, shadowy lines that resembles woven fabric. Is typical of ADR materials like flame-fusion synthetic spinel. A good way to distinguish synthetic from natural spinel.
Double-Brush Biaxial Optic Figure
A figure that resembles a uniaxial optic figure because the angle between the optic axes is so small the brushes seem to intersect.
Interference Colors
The iridescent colors that result from the interaction of light rays traveling along the same path. Find them first to help locate the gem’s optic figure.If you can’t find colors, look for a brush that sweeps across the stone. Touch the optic figure spere to the brush’s narrowest point to find the optic figure.
Isochromes
The concentric rings of an optic figure
Optic Figure
A characteristic light pattern that helps identify a gem’s optic character
Polariscope
An instrument that helps you study the interaction of transparent-to-translucent gems with polarized light
Polarizer
The polariscope’s lower polarizing filter, which remains stationary
Uncrossed Filters
The polariscope’s open, or light, position, with the light-transmitting directions of the analyzer and polarizer parallel to each other.
