The price of a gem depends on its optical properties. Optical properties are essential to the beauty of a gem. The better the optical properties, the higher the price. Gems can be precious or semi precious, however, it does not mean that the precious gem is always more expensive than the semi-precious one. If the latter is more attractive and more beautiful, then it is costlier.
An optical property is composed of color; dispersion (refers to the scattering or bending of light into different colors by refraction or diffraction); refractive index (this the measurement of the bending of light or the so-called refraction); and pleochroism (the display of a variety of colors when viewed at various axes). Gems are commonly prized because of their asterismal property (this is produced by the refraction of light, presenting a six-rayed star-like effect on the gem), chatoyant effect (the changing of colors just like a cat’s eye), iridescence (this is the display of rainbow-like colors on the surface of the gem) and adularescence (the whitish and bluish light on the gem when turned, commonly seen in the gem moonstone).
The role of the polariscope is to determine whether the stone is isotropic or anisotropic or at most, the optic character of the gems before they are used to create jewelries. It is one of the tools used in gematology and uses polarized light to identify the gem’s characteristics. Two polarized filters comprise a polariscope, one at the top and one at the bottom. The one at the top is called analyzer, while the one at the bottom is called the polarizer. Each has its own vibrational planes. When the direction of the polarizer’s vibrational plane is perpendicular to the direction of the analyzer’s, this creates a position called “crossed position” (this means that the space between the polarizer and the analyzer is dark). This reaction of the two vibrational planes will determine whether the gem is isotropic, anisotropic, anomalously doubly refractive or anisotropic aggregate.
Here are the steps in using polariscope:
- Turn on the light switch of the polariscope.
- Rotate the analyzer (it is located at the top of the instrument) to “crossed position”. This is when the field between the two filters becomes dark, also called “dark position” or ‘extinction position”.
- Insert the gem between the analyzer and the polarizer.
- Using a tweezer or small tong, rotate the gem 360 degrees. If you see that the gem remains dark during the entire rotation, then it is isotropic or single refractive.
- If the gem displays patterns resembling snakeskin during the rotation, then it is anomalously doubly refractive or ADR.
- However, if the gem blinks four times, alternating light and dark, during the whole 360 degrees rotation, then it is anisotropic.
- But if the gem appears full of light as soon as you place it under the analyzer and as you rotate it 360 degrees, the light stays, then it is classified as microcrystalline or cryptocrystalline aggregate.
Jewelry making requires not just the design but also the quality of the gemstone. The design must compliment or enhance the natural characteristics of the gem to create a very attractive piece.