Examining a diamond

Details Examining a diamond Examining a diamond

1997-06-19

1999-03-16

Hannaher, Constantine

Radiant energy

Infrared-to-visible imaging

356 30, G01N 2187

Patent

active

058833889

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a method of and apparatus for examining a diamond. For example, the invention may be used to test whether a diamond has had a layer of synthetic diamond deposited thereon. This is of particular importance in detecting whether the diamond comprises CVD diamond material and also in locating such material if present.
The synthetic diamond material may be deposited on an uncut or part-worked natural diamond which is then worked, for example, into a round brilliant cut. Alternatively, the synthetic diamond 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 1 .mu.m to 0.1 mm.
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 that has.
Over the years, a number of methods of synthesising diamond material have been developed. One of these methods is the chemical vapor 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 method which is most likely to be used to deposit synthetic diamond onto 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 diamond substrate. 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 determining 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 practiced jeweller who has no training in laboratory gemological analysis.


THE INVENTION

The present invention provides a method of testing whether a diamond has had a layer of synthetic diamond deposited thereon, comprising comparing observations of infra red radiation emanating from each of a plurality of zones of the diamond, to detect differences between the compositions of different zones of the diamond, the radiation observed including radiation of wavelength substantially in the range 7 .mu.m to 25 .mu.m, preferably 7 .mu.m to 10 .mu.m.
The present invention also provides apparatus for testing whether a diamond has had a layer of synthetic diamond deposited thereon, comprising means for observing infra red radiation emanating from a zone of the diamond which is substantially smaller than the total surface area of the diamond, the radiation observed including radiation of wavelength substantially in the range 7 .mu.m to 25 .mu.m, preferably 7 .mu.m to 10 .mu.m.
The present inventors have discovered that where the intensity of infra red radiation of the abovementioned waveband emanating from a diamond is different between different zones, it may be concluded that the diamond has had a layer of synthetic diamond deposited thereon. Where there are no such differences, it may be concluded that the diamond is substantially of one type. Care should be taken, as explained below, to distinguish low ob

REFERENCES:
patent: 3721289 (1973-03-01), Seal
patent: 4875771 (1989-10-01), Bowley et al.
patent: 4915827 (1990-04-01), Rosenthal
patent: 5386117 (1995-01-01), Piety et al.
patent: 5396068 (1995-03-01), Bethea

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