Heat treatment is most commonly used to alter color but is also used to increase clarity. Heating is used to either lighten, darken or alter the color of a gem. Amethyst is heated to lighten its color. Heat a little more and some sources of amethyst will alter color from deep purple to orange colored citrine.Click to see full answer. Considering this, how are sapphires heat treated?Heat treatment is used to improve a sapphire’s color, remove color zoning , and improve clarity. Over the last couple of decades, high temperatures in excess of 1700 degrees Celsius has been applied to sapphires, which improves clarity by dissolving silk as it improves color.Also Know, what is unheated gemstone? Unheated Gems. The reality is that only a very small percentage of well-known gemstones are considered “gem quality” without some form of treatment. One of the most common types is heat treatment, used to enhance already existing color, reduce inclusions, or produce a desirable color. Also to know, what natural gemstones can be treated in a lab? Common heat-treated gems include amber, amethyst, aquamarine, citrine, ruby, sapphire, tanzanite, topaz, tourmaline. High Heat High Temperature (HPHT) – used for diamonds. Changes brown diamonds permanently to colorless, or to yellow, orange, blue.How do you heat treat Topaz?heat treatment and irradiation of topaz. generally topaz becomes strongly electrified by friction or heat or some stones by stroking. Heat-treated reddish-brown topaz form Brazil in a sand bath of 500°C turns color to pink.