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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How to tell that you have purcahse a Glass filled Corundum / Composite Corundum / Hybrid Corundum (ruby / Sapphire) ?

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Glass Filled Corundum Identification

Since the 1980s, silica glass has been widely used to fix voids and fractures in rubies. Cavity filling was first seen and documented in 1984. (Kane, 1984). This filling improved the face-up appearance of the stones and may have added weight, but it was also easily detectable under magnification.

Identification Features of Glass filled corundum: when you see glass filled corundum through the gemological microscope. There are two main features in glass filled corundum will be observed:

  1. Air bubbles
  2. Blue flash effect

In the pictures below you will observe the bluish fleshes and a lot of air bubbles. So the identification of the glass filled / composite corundum / hybrid corundum is too easy.

It is not necessary that you have an expensive gemological microscope but the same scene can also be viewed in 10x loupe / eyeglass / magnifying glass which price is only a few dollars.

Inclusions in Glass Filled rubies 

Glass Filled Ruby


Air bubbles and bluish fleshes in glass filled corundum (ruby)

age showing air bubbles and blue flash effect in a glass filled ruby.


Glass Filled Ruby

Air bubbles and bluish fleshes in glass filled corundum (ruby)

Image showing air bubbles and blue flash effect in a glass filled Ruby




Air bubbles and bluish fleshes in glass filled corundum (ruby)


Air bubbles and bluish fleshes in glass filled corundum (ruby)


Air bubbles and bluish fleshes in glass filled corundum (ruby)


Air bubbles  glass filled corundum (ruby)


 

Location: Pakistan

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