Sunday, 26 January 2014

Synthetic Diamonds Primer

Dating back to the 19th century, there have been many claims for the creation of diamond in a lab.
For many years conventional wisdom was that diamond would form only under conditions of high pressure and high temperature (HPHT).

The first commercially available “manmade” diamond was produced at high pressure and high temperature by General Electric in 1956. HPHT growth imitates natural diamond formation, but with carefully selected input materials to catalyze crystal growth. Today, billions of carats of diamonds are manufactured annually by the HPHT process, mostly for industrial applications.
In 1954 a patent was issued for another type of diamond growth: the CVD (chemical vapor deposition) process. In the late 1980s, scientists discovered how to reproducibly grow diamond using the CVD process.

The CVD process is quite different from natural diamond formation. It produces diamond from a heated mixture of a hydrocarbon gas (typically methane) and hydrogen in a vacuum chamber at very low pressures.
The CVD process produces gem-quality synthetic diamond of great beauty, with properties virtually identical to those of natural diamond. Because of their high purity, these CVD products are type IIa.
Detection has advanced to the point where any CVD-grown sample can be identified with certainty. The CVD growth process itself occurs under conditions that bring about readily detectable features, including:

1. a low-pressure, highly energetic hydrogen-rich environment
2. the presence of silicon from grower parts
3. the presence of residual nitrogen in the grower
4. the layer-by-layer addition of carbon atoms on the growing surface


SURAT: Experts appointed by Gems and Jewellery Export Promotion Council (GJEPC) to understand the landscape of man-made (synthetic or lab-grown) diamonds and its likely impact on the industry have started a secret operation to find out the units manufacturing synthetic diamonds in a clandestine manner in the world's biggest diamond cutting and polishing centre in Surat.

The small diamond manufacturers in the diamond hub of Varachha and Katargam have come under the scanner following reports of the large-scale mixing of synthetic lab-grown diamonds in the natural diamond parcels. Sources said there are some unscrupulous elements in the diamond industry polishing synthetic stones at secret locations in the city.

The polished synthetic diamonds are then mixed with natural diamonds and sold in the diamond markets located at Mahidharpura and Varachha.

Thursday, 9 January 2014

Hydrophane Opal

Hydrophane (Greek: hydro - water; phane - cause to appear) is a variety of opal that appears dull and turbid until immersed in water, it emits streams of bubbles, often accompanied by appropriate noises. It slowly becomes translucent and in some cases, totally transparent with play-of-colour.

Some examples show the opposite effect: precious opal loses play-of-colour when immersed in water. They are very rare and are called "Reverse Hydrophane".