Radiant energy – Invisible radiation responsive nonelectric signalling – Luminescent device
Reexamination Certificate
2001-01-19
2001-12-18
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiation responsive nonelectric signalling
Luminescent device
C250S372000, C250S559400
Reexamination Certificate
active
06331708
ABSTRACT:
BACKGROUND TO THE INVENTION
The present invention relates to a method of and apparatus for testing whether a natural diamond has had a layer of synthetic diamond deposited thereon. This is of particular importance in testing whether the diamond is wholly natural or whether any part of it comprises CVD diamond material and also in locating such material if present.
Synthetic diamond material may be deposited on an uncut or part processed 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 microns to 10 microns) 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 (ie mined) 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, although alternative techniques such as physical vapour deposition have been proposed. A diamond artificially enlarged by deposition of CVD or similar 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 as “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.
A method of testing whether a diamond has had a layer of synthetic diamond deposited thereon is disclosed in British Patent Application No. 9401354.7 published as GB2286251A. A plurality of parts of the diamond are irradiated with radiation substantially of wavelength substantially in the range 230 nm to 320 nm and the transmission of the irradiating radiation by the diamond is observed.
The invention of GB 9401354.7 is based upon the observation 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 a layer of synthetic diamond deposited thereon. It is further observed 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.
The intensity of radiation transmitted by the zones of the diamond may be investigated using an imaging apparatus or by placing the diamond in an integrating sphere. Preferably, an image of the diamond is formed against a dark or light background.
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, in which relatively simple imaging apparatus is used and an expensive integrating sphere is not required.
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 testing whether a diamond has had a layer of synthetic diamond deposited thereon, comprising:
directing a beam of ultraviolet radiation towards a face of a diamond, so as to form a pattern of beams of radiation due to refraction and reflection of the irradiating radiation, and observing the pattern of such beams of radiation substantially of wavelength substantially in the range 230 nm to 320 nm
The present invention uses the same principles of absorption of certain wavelengths of ultra-violet radiation by certain types of diamond as used in GB 9401354.7.
It is known from documents such as U.S. Pat. No. 3,947,120 that where light is directed towards a cut gemstone, a pattern of spots of reflected and refracted radiation may be produced which is characteristic of each gemstone
The present inventors have discovered that the different interaction of different types of diamond with ultraviolet radiation of the waveband in question can affect the pattern of spots obtained and help to identify superficial synthetic diamond layers.
In simple terms, substantial differences in the complexity and intensity of beams produced by different parts of the diamond (allowing for the shape of the diamond) indicate the presence of synthetic layers on the diamond.
In detail, the invention 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 diamond. Thus natural diamond is generally expected to give weak or unobservable reflected and refracted beams with radiation of wavelength shorter than 320 nm.
A synthetic diamond layer is generally expected to give a complex pattern of reflected and refracted beams. Any diamonds which give results suggesting the presence of a synthetic layer should be referred for further testing.
Preferably, substantially the whole of the present face of the diamond is irradiated. This allows a complete pattern of beams to be formed and observed.
In principle, a single observation of the pattern of refracted and reflected beams of radiation could be sufficient to reveal the presence of a layer of synthetic diamond material. If, for example, a substantially symmetrical face of the diamond is exposed to the radiation and an asymmetric pattern of beams is obtained, the presence of layers of synthetic diamond may be suspected.
However, it is preferable to direct the beam of radiation to the diamond from a number of directions in succession and to compare the patterns obtained. Interpretation of the results will be discussed further below.
It may be sufficient to test only a few faces (maybe only two) in order to detect a difference in the pattern of reflected and refracted beams. Preferably, however, a large number of faces are irradiated in succession.
The diamond may be irradiated with suitable radiation (as discussed below) by exposing it to radiation from a suitable source. The irradiating radiation may be focussed if necessary.
The beam of irradiating radiation may be of size less than the presented face of the diamond but is preferably greater in size.
In the invention, the pattern of reflected and refracted beams observed does not correspond to the image of the diamond. What is observed is the pattern produced where the reflected and refracted beams intercept a notional plane displaced from the diamond. A screen or scanning means may be placed at this notional plane. The scanning means may measure the intensity of light at each point on the notional plane to thereby record the pattern of reflected and refracted beams.
Preferably, the pattern of reflected and refracted b
Cesari and McKenna
Gabor Otilia
Gersan Establishment
Hannaher Constantine
LandOfFree
Examining a diamond does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Examining a diamond, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Examining a diamond will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2579353