A dichroscope is a gem-testing instrument that shows a stone's two pleochroic colors side by side. In the calcite type, a calcite rhomb splits the light into two images of a small window.
In more detail
The two images carry light that vibrates at right angles. Two different colors show that the stone is doubly refractive and pleochroic. Matching colors prove nothing: a singly refractive stone, a colorless one, or a view down the optic axis all match. A London dichroscope uses two polarizing filters instead of calcite.
How we measure it
Our Dichroscope computes the window colors from measured polarized absorption spectra, through 5 mm in daylight (D65). It is a teaching model, not a test of a real stone.
Related terms
- Pleochroism: Pleochroism is the property of a colored doubly refractive stone to show different colors in different directions. It happens because the stone absorbs its rays differently.
- Ordinary ray: The ordinary ray (o-ray) is the ray in a uniaxial stone that vibrates across the optic axis. It has the same refractive index, ω or nₒ, in every direction.
- Extraordinary ray: In a uniaxial stone, the extraordinary ray (e-ray) vibrates in the plane of the optic axis and the light path. Its refractive index changes with direction, from ω along the axis to ε across it.
- CIEDE2000 color difference: CIEDE2000 (ΔE00) is a standard formula for how different two colors look to a human observer. A larger number means a larger visible difference.