Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Patent
1996-09-23
1998-09-22
Le, Que
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
356 30, G01N 2186
Patent
active
058118241
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND TO THE INVENTION
The present invention relates to a method of and apparatus for testing whether a diamond has had a layer of synthetic diamond deposited thereon. This is of particular importance in testing whether the diamond comprises CVD diamond material and also in locating such material if present.
Synthetic diamond material may be deposited on an uncut natural diamond which is then worked, for example, into a round brilliant cut. Alternatively, the synthetic diamond material coating may be deposited onto a fully fashioned brilliant stone after working of the stone. The thickness of the synthetic diamond material layer may be very thin (it could be in the range from 5 .mu.m to 10 .mu.m) but the present invention may also be used to detect thicker layers.
The value of a diamond is in part dependent upon its weight. Accordingly, synthetic diamond material may be deposited onto natural gem diamonds, before or after cutting of the diamond, to increase the weight of the finished product.
However, the value of a diamond also resides in its qualities of authenticity and uniqueness and in the fact that it is an entirely natural product. Thus, a diamond that has not been enlarged by deposition of synthetic diamond material has a value over a diamond which has.
Over the years, a number of methods of synthesising diamond material have been developed. One of these methods is the chemical vapour deposition (CVD) technique, which is a low pressure technique involving deposition of synthetic diamond (referred to as CVD diamond material in this specification) onto a substrate from a gas. CVD is the most likely way in which synthetic diamond will be deposited on a diamond. A diamond artificially enlarged by deposition of CVD diamond material is referred to in this specification as a "CVD
atural diamond doublet".
CVD diamond material may be deposited on a non-diamond or diamond substrate. In the latter case, the CVD diamond material can replicate the structure of the diamond substrate (referred to "homoepitaxial growth"). The CVD
atural diamond doublet produced can be identical in appearance, density and other common physical properties to an entirely natural stone and there may be a problem in identifying such a CVD
atural diamond doublet.
It is an object of the present invention to provide a method of and apparatus for testing whether a diamond has had a layer of synthetic diamond deposited thereon.
It is desired that the apparatus should be simple and inexpensive and may be put into operation by a person with relatively little training. The method and apparatus should be capable of being operated reliably and consistently by a practised jeweller who has no training in laboratory gemological analysis.
THE INVENTION
The present invention provides a method of and apparatus for testing whether a diamond has had a layer of synthetic diamond deposited thereon, as set forth in claim 1, 16 and 26. Claims 2 to 15 and 17 to 25 set forth preferred and/or optional features of the invention.
The present inventors have discovered that where different zones of a diamond show differences in their absorption of radiation substantially of wavelength substantially 230 nm to 320 nm, it may be concluded that the diamond in question has had a layer of synthetic diamond deposited thereon. An imaging apparatus or integrating sphere is found to be suitable for investigating a diamond in this way.
The present inventors have further discovered that if all zones of a diamond strongly absorb radiation substantially of wavelength substantially 230 nm to 320 nm, the diamond may be classified as almost certainly a wholly natural diamond.
This is based upon the observation that the majority of natural diamonds are classified as type IaA or IaAB and very strongly absorb ultraviolet radiation of wavelength shorter than approximately 320 nm, whereas a synthetic diamond layer will normally be of a type which strongly absorbs ultraviolet radiation of wavelength shorter than approximately 230 nm, in particular type II.
A very small numbe
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patent: 4152069 (1979-05-01), Bruck
patent: 4259011 (1981-03-01), Crumm et al.
patent: 4508449 (1985-04-01), Okazaki
patent: 5118181 (1992-06-01), Yifrach et al.
patent: 5164586 (1992-11-01), Hohberg et al.
Cooper Martin
Smith James Gordon Charters
Smith Martin Phillip
Gersan Establishment
Le Que
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