How to Check for a Heat-Treated Stone

Hold the gemstone under a desk lamp or bright light and examine the color under a jeweler’s loop. If the gemstone has been exposed to high temperatures, the primary color of the gemstone will appear brighter, while the other colors fade into the background.

Look for multiple colors in the gem. A non-heat-treated gemstone should show more than one color or multiple shades of the same color. Sapphire, for example, should show two shades of blue inside the stone when exposed to light.

Check the stone for a halo effect. When heat touches the stone, it causes fractures in the middle of the gem. The fractures span throughout the inside, giving the appearance of a halo. High-quality, unheated stones lack this halo effect.

Take the stone to a reputable jeweler in your area. Jewelers have access to tests that you cannot perform at home. Depending on the type of stone, the jeweler may need to send the gem for testing, which, while expensive, can tell you definitely whether your stone is heat-treated.