The color saturation is present even in its rough unheated form - a deep molasses like color will heat to a deep blue or blue violet. So the more "washed-out" or pale the color in Tanzanite the lesser the grade. the deeper the color saturation the finer the stone. Heating is not a color enhancer in Tanzanite’s case. Displays the effect heating has on Tanzanite's color. The yellow-green component is removed with heating at 600 degrees centigrade, resulting in the blue or purple final color.
It is a strongly trichroic gemstone with 3 colors - reddish-violet, blue, and yellow-green all combining to produce a brown treacle-like hue. Tanzanite before heating resembles treacle in color. It is assumed that all Tanzanite is heat treated. Tanzanite: Tanzanite is an interesting case as the blues we know and love would not exist without heating. Heating repairs crystal structural damage, reducing the yellow component, and turning the topaz pink. Topaz : Brown/Orange Topaz is routinely heated to produce Pink Topaz. If these gems are the finest color they will command premium prices due to their extreme rarity. Unheated rubies and sapphires will contain microscopic rutile needles or tiny gas bubbles in pockets of liquid which are evidence that laboratories can use to guarantee that these stones have not been heated. A large percentage of ruby and sapphire on the market today is heated and it is a fairly routine treatment. Leaving a more transparent and therefore more beautiful gemstone. The rutile which forms the silk dissolves into the stone at high temperature (usually around 1800 degrees centigrade). Heat causes structural changes in “silk” inclusions in ruby and sapphire. Unlike Beryl it is not usually done to enhance color as such, but transparency, and it is not an atomic change but a structural one. The change is caused by an alteration in atomic structure, namely F3 molecules becoming F2 molecules.Ĭorundum : Heating of corundum, notably Ruby and Sapphire varieties is a widespread and common occurrence. Heating to approximately 400 degrees centigrade will remove the yellow, leaving just the blue. The 2 colors together make green which is why most unheated aquamarine is a greenish blue color. Color in Aquamarine is caused by iron impurities and it generally has 2 colors – yellow and blue. This is done by heating bubbles within amber to a point where they implode making discoid fractures which reflect light causing a “spangled” effect.īeryl : The blue-green variety of Beryl - Aquamarine is a routinely heated gemstone. Additionally, heat can be used to produce tiny fractures called sun spangles” in the trade. The bubbles can be removed by slow heating, generally whilst immersed in rape or linseed oil. Some Amber also contains gas bubbles that can make it appear cloudy. Some of the more commonly heated gemstones and the impact of heat upon them are:Īmber : Gentle heating oxidizes and darkens Amber. Heat usually affects a material’s color by altering the chemical state of some of its atoms and thus its light absorbing pattern, but it can also change appearance in other ways.
It all depends on a number of factors including pressure, temperature, rate of heating and cooling and chemistry.
It can eliminate inclusions or it can form them. Heat can lighten, darken, deepen or change a gemstone’s color entirely. Gemological Oven - newly heated Tanzanites being removed from a specialized gemological oven History tells us that people in India were heating dull yellow chalcedony to produce bright orange carnelian as early as 2000BC. It is one of the oldest and most common treatments.
This is a treatment that has been used for centuries. This article will take a look at two of the most common forms of treatment, heating and irradiation. Some are accepted as normal practice in the trade and are a routine part of a gem type’s route to market and others are unscrupulous attempts to misrepresent lower grade gemstones as fine pieces. Some treatments are permanent, others are not. Sometimes, these treatments can transform a gemstone completely. Anyone who has an interest in gemstones and a passing knowledge of the trade will know that there exist many forms of treatment and enhancement devised by man to make lower grade gems look better.
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