Editing Gemstone (section)

=== Heat ===
Heat can either improve or spoil gemstone color or clarity. The heating process has been well known to gem miners and cutters for centuries, and in many stone types heating is a common practice. Most [[citrine quartz|citrine]] is made by heating [[amethyst]], and partial heating with a strong gradient results in "[[ametrine]]" – a stone partly amethyst and partly citrine. [[Aquamarine (gemstone)|Aquamarine]] is often heated to remove yellow tones, or to change green colors into the more desirable blue, or enhance its existing blue color to a deeper blue.<ref name = enhancement/>

Nearly all [[tanzanite]] is heated at low temperatures to remove brown undertones and give a more desirable blue / purple color.<ref>{{cite web |url=http://www.lapigems.com/blog/post/2013/01/17/Tanzanite-Heating-The-Facts.aspx |title=Tanzanite heating – the science |archive-url=https://web.archive.org/web/20160620222334/http://www.lapigems.com/blog/post/2013/01/17/Tanzanite-Heating-The-Facts.aspx |archive-date=2016-06-20 |df=dmy-all}}</ref> A considerable portion of all [[sapphire]] and [[ruby]] is treated with a variety of heat treatments to improve both color and clarity.

When jewelry containing diamonds is heated for repairs, the diamond should be protected with [[boric acid]]; otherwise, the diamond, which is pure carbon, could be burned on the surface or even burned completely up. When jewelry containing [[sapphires]] or [[rubies]] is heated, those stones should not be coated with boric acid (which can etch the surface) or any other substance. They do not have to be protected from burning, like a diamond (although the stones do need to be protected from heat stress fracture by immersing the part of the jewelry with stones in the water when metal parts are heated).