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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Aquamarine that has been dyed and marketed as a natural emerald

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Dyed aquamarine sold as a natural emerald 


Recently our lab CIGTL-Pakistan received a green stone for confirmation whether it is an emerald or an imitation of an emerald. When properly checked on the different gemological instruments, it is observed that the stone belongs to a beryl group. But when seen through a gemological microscope the color concentration in cracks is observed. The light blue color is also observed in the corner and in the middle where it is free from cracks. So be aware of this type of material. Before buying gemstones first test in a reputed laboratory or, buy from a reputed seller.
 

Dyed aquamarine sold as natural emerald
Dyed aquamarine sold as a natural emerald 



Dyed aquamarine sold as natural emerald
Dyed aquamarine sold as a natural emerald 

Dyed aquamarine sold as natural emerald
Dyed aquamarine sold as a natural emerald 




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