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Showing posts with the label Heat Treatment

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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Low-Temperature Heating of Pink Sapphire: Why Detection Can Be Difficult

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A pink sapphire with a violet component may become a cleaner pink after heating. Detecting this change can be difficult when the heating leaves little obvious damage inside the stone. The word low-temperature is relative: the temperatures involved are still extremely high. What the experiments showed SSEF’s 2010 article describes research on pink sapphires from Madagascar and East Africa. Heating around 800–1000°C could reduce the blue component. The researchers also studied samples at several lower and higher experimental temperatures. The important lesson is that familiar microscopic signs of intense heating can be scarce after lower-temperature treatment. A stone that lacks melted-looking inclusions is not automatically proven unheated. Zircon inclusions as evidence The study investigated zircon inclusions with Raman spectroscopy. Heating could alter their crystal condition and the shape of their spectral peaks. Measuring these changes provided evidence that was less obvious ...
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