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Karl Schmetzer
Abstract: The relevant patent literature describing high pressure high temperature treatment processes of natural and synthetic diamonds is reviewed. A general overview about high pressure high temperature treatment for various technical applications is presented and colour changes for jewellery-quality diamonds are described in detail. Three major groups of patent documents exist that deal with the treatment of intense yellow type Ib synthetic diamonds, the colour alteration of brown natural diamonds and colour improvement of chemical vapour deposition grown synthetic diamonds, respectively. The reaction mechanisms involved in various processes of colour alteration are briefly discussed.
In this extended version on the worldwide web, the different types of patent documents are explained, and the most relevant technical descriptions of a range of equipment used to perform HPHT treatment of diamonds are summarized in appendices.
All the Journal articles placed online in 2010 will also be published in hard copy as a single Journal issue and sent to all paid-up Gem-A members early in 2011 as part of their 2010 subscription. Gem-A members may login to the membership area to view the full articles.