Gemstone Windows and Dark Patches: What to Look for in a Cut Gem

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AI-generated educational illustration. Conceptual only; not a photograph of an actual specimen or location. A coloured gem may have a pale, see-through centre or areas that look almost black. Both affect its appearance, but they do not have the same cause. What is a window? A window is an area where light passes through the gem instead of being returned towards the viewer. You may see the background through it, especially near the centre. Cutting angles and the material's refractive index—how it bends light—help determine whether this happens. There is no single ideal depth for every gemstone. Why dark patches need a closer look Darkness can have several causes. The material may absorb a lot of light. Some facets may reflect dark surroundings or the observer. Extinction is another cause, involving light that is not returned to the viewer after internal reflection. For that reason, calling every black patch “extinction” can be misleading. A simple viewing routine Look at the gem fac...
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Basic Terms used in Gemology

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Basic Terms used in Gemology

Real or Natural gemstones: Real or Natural Gems are those which are entirely the product of nature and unaltered by humans in any way, except for ordinary cutting and polishing.

Treated gem: Any gem material which has been altered by humans, beyond ordinary cutting or polishing. For example Diffusion sapphire, Glass filling Ruby, dying, heat treatment etc.

 

Synthetic gems: Same as natural gem ( in terms of composition, structure, properties and appearance), except made by man. Or The Gems which have natural counterpart. For example Synthetic Ruby, sapphire etc.

How to grown synthetic quartz in laboratory by hydrothermal process?



 

Simulant or imitation: A material ( Natural or Synthetic), Which has the same appearance as the gem it imitates(look like) but different chemical composition. For example Cubic Zirconia imitating Diamond, Red Garnet is the imitation of Ruby.

 

Assembled gems or composite gems: A gem material (Natural or Synthetic), which is produced by assembling two or more pieces of the like or unlike material along a distinct junction. For example opal triplet, garnet/glass doublet.

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