Polariscope-Microscope
Polariscope-Microscope
A gemmological microscope built around crossed polarising filters for high-magnification optical work
A polariscope-microscope is a gemmological microscope fitted with a fixed polariser below the stage and an analyser above the objective, allowing the gemmologist to examine stones under crossed-polarised light at the magnifications of a research-grade instrument. The configuration combines two functions that are usually housed in separate tools — the bench polariscope used for routine optic-character work, and the gemmological microscope used for inclusion study — into a single, more capable instrument.
Configuration
The polariser is mounted below the well or stage, oriented so that light passing upward through the sample is plane-polarised before it reaches the gemstone. The analyser sits in the optical path above the objective, oriented at ninety degrees to the polariser when crossed. Most models allow the analyser to be rotated in and out of the path, so that the operator can switch between polarised and unpolarised observation without re-mounting the stone. A first-order red plate, sensitive tint plate, or quartz wedge accessory is sometimes provided for refined retardation work.
What it reveals
Under crossed polars at magnification, internal strain becomes visible as patches and bands of anomalous interference colour. Strain in glass, synthetic flame-fusion corundum, and synthetic spinel produces characteristic patterns: tatami strain in flame-fusion ruby and sapphire, snake-like or roiled strain in glass, and cross-hatched strain in synthetic spinel. Twinning planes in natural corundum and other anisotropic species are also brought out clearly. The instrument is the standard tool for high-resolution observation of the optical character of small inclusions and for resolving fine zoning that a low-power polariscope cannot.
In the laboratory
Polariscope-microscopes are standard equipment in advanced inclusion-study laboratories and in research settings where the gemmologist needs simultaneous high magnification and crossed-polarised illumination. They are less commonly seen on the dealer's bench, where a separate polariscope and stereo microscope are the more economical pairing. Operators often work with the analyser in and out alternately, comparing the two views to confirm what they are seeing.