On a colored gemstone, the application of controlled high temperatures to alter or improve its color and/or internal structure. Heat enhances many types of gemstones. And it achieves this by essentially continuing the process started by nature. For example, heat can turn a naturally brown tanzanite into a striking blue/violet, or transform a cloudy ruby to a distinct red. Pearls can also be treated with high temperatures to modify color. However, heat is often used with other treatments, such as bleaching, to maximize effects.