Why Heat treatment is done to Gemstones?

Heat treatment is the most common treatment and without heat treatment the availability of fine gems would be significantly less. With less gems prices would be dramatically higher only available to the rich. This is the reason untreated gems often command 30% to 50% higher prices. 

Sapphires, rubies, aquamarine, tanzanite, amethyst, citrine, blue topaz, blue zircon, tourmaline, and others are commonly treated with heat. The temperature and time required to alter color varies dramatically from 400 degrees Fahrenheit to 1300 degrees are commonly used to alter color.

WHY HEAT TREATMENT IS USED

Heat treatment is most commonly used to alter color but is also used to increase clarity. Rubies and sapphire can require significantly higher temperature to alter color and change 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. Uraguay is a good example. Heat a little more and amethyst can go colorless or milky, neither of these are desirable. Tanzanite is heated to around 1000 degrees Fahrenheit. Tanzanite is a trichroic gem with blue, violet and yellow colors which in the rough appears as a color known in the trade as "diesel". If you look into a can of diesel fuel this is what fine tanzanite rough looks like, a brownish bluish red color. Upon heating the gem is left with the blue and violet we know as tanzanite. The yellow is permanently gone.

Aqua heating is also removing the yellow component which gives natural aqua a green tint. After heating the gem is left without the green giving it a blue color of similar intensity. Green tourmaline is often heated to lighten color in over saturated gems, like those commonly seen in Brazil. Other tourmalines are heated to alter one of the dichroic colors. Sapphire is one of the few gems which the color can be darkened by heating as seen in Ceylon Sapphire. Grey silky material known as Geuda can be changed to blue by heating.

Difference Between Heated And Natural Ruby Gemstone

Heated Ruby Gemstone:

A ruby stone is heating with the intent of improving its color and luster of the stone. It is a useful process through which a high-quality ruby stone can be obtained. Notwithstanding, there are some disadvantages of implying heat on a ruby. Since ruby is a naturally occurring gemstone and heating it on high temperature will disturb the originality of this stone.

Heating a ruby can albeit improve or outshine its exterior appearance, but its actual properties will be lost or deteriorated. But, if this technique is cause it will prove auspicious, sadly, most of the time due to lack of expertise the natural qualities of ruby vanish because of excessive heating. Therefore, heating is not an appropriate option.

Unheated Natural Ruby Gemstone:

Unheated ruby stone is natural ruby gemstones. By unheated rubies, we mean original rubies which are mined directly from different part of the world. Most of the rubies are enhance in attempt to make it replace unheated ruby stone by introducing heat treatment which upgrades the color and shine of the stone.

Nonetheless, a heated ruby gemstone even after receiving artificial uplifted can’t compete with unheated rubies on quality parameters. An unheated ruby or Manik gemstone is extracted from famous mines. Unheated Burmese ruby and unheated Madagascar rubies are best in class.

Heat treatment is a very risky process as many gems have inclusions that expand at a different rate and cause stress fractures, which then becomes an identifying characteristic of heated gems, particularly sapphire and ruby which can display halos around inclusions within the gem.

Ruby is highly valued for being natural and can command more that 50% greater value than a similar treated gem. Unheated Sapphires command an estimated 30% premium over similar heated gems. Natural ruby and sapphires are more durable as they tend to have greater resistance to chipping. Other gems usually bring 10-20% higher value when of natural color.