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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The Chemistry of Color in Diamonds: How Impurities Create Unique Hues

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Cause of Color in Diamond

The color in a diamond is caused by the presence of certain impurities or structural defects in the crystal lattice of the diamond. These impurities or defects can absorb certain wavelengths of light, resulting in the diamond appearing to have a specific color.

Some common causes of color in diamonds include:

  • Nitrogen: Nitrogen impurities can give diamonds a yellow or brown color.
  • Boron: Boron impurities can give diamonds a blue color.
  • Hydrogen: Hydrogen impurities can give diamonds a purple color.
  • Structural defects: Structural defects in the diamond's crystal lattice can cause color variations such as green or pink.

The presence and concentration of these impurities or defects determine the intensity and hue of the diamond's color.

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