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Heat treatment. What it is?
The heat treatment process itself is the most common refinement method. It implies a high-temperature effect on the stone. The purpose of applying heat treatment to faceted inserts is mainly to improve or change the color of the stone. In addition, this type of refinement can make the stone visually cleaner, so in the process of heat treatment these or those inclusions will dissolve. The heating process itself, the temperature regime, the environment in which the stones are annealed and other conditions, for different types of stones are significantly different. For example, rubies and sapphires are annealed in a reducing medium up to 1800 degrees, as a result of which rutile inclusions dissolve and titanium, together with iron or chromium, acting as chromophores, color corundums in blue or red. Whereas amethysts to obtain citrines from them heat up to 450 degrees. Approximately the same temperature range (400-450 degrees) is used to process aquamarines to enhance blue color and for orange beryls to obtain a pink tint. Another stone that is often exposed to heat is zircon, brown varieties of which are heated to 1000 degrees in an oxygen-free environment and get a blue color.
Also, the heat treatment method can be used with other refinement methods, most often with radiation. An example of such a refinement is the processing of topaz. So the sky blue color for it is obtained by electron irradiation followed by annealing, and the intense blue color London, fashionable in the jewelry market, is obtained by neutron irradiation in combination with annealing.
В геммологической практике бывают весьма увлекательные случаи с диагностикой ювелирных вставок
Но помимо редкости цвета и высокой стоимости таких камней, многие розовые камни выделяются одной замечательной особенностью – они проявляют плеохроизм, то есть в зависимости от положения осмотра камня он может иметь дополнительные оттенки – оранжевый или пурпурный.
Currently, gemstones are produced by two fundamentally different technological methods - the High Pressure - High Temperature method (“HPHT”, High-pressure & High-temperature) and the Chemical Vapor Deposition (“CVD”, Chemical vapor deposition) method. The "HPHT" method is the most tested classical synthesis method, which can be used both carbon deposition on diamond from flux melts and catalytic reactions. In "CVD" synthesis, diamond growth occurs on a seed during carbon deposition mainly from a gaseous medium at relatively low temperatures and pressures.
Jewelry and precious stones are just such a category of goods, when buying which you need to pay attention to many criteria.
Sogdianite is a rather rare mineral and more often it can be found as a collection material (moreover, in systematic collections), and it is extremely rare in jewelry.