| abstract |
A process for imparting colour to, or enhancing the colour of, gemstones such as topaznand sapphire involves the coating of the gemstone substrate with a colour-inducing orncolour-enhancing material, and heating to a temperature in the range 900°C to 1,250°Cnfor a period of 30 minutes to 10 hours. Suitable coating materials are metals, metalnoxides, other metallic compounds, and alloys. By appropriate selection of coatingnmaterial, for example from among cobalt, iron, chromium, and compounds and mixturesnthereof, a range of colours including blues, greens, oranges and reds may be produced. |