U.S. patent application number 09/766338 was filed with the patent office on 2001-09-27 for examining a diamond.
Invention is credited to Smith, Martin Phillip.
Application Number | 20010023925 09/766338 |
Document ID | / |
Family ID | 26307449 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010023925 |
Kind Code |
A1 |
Smith, Martin Phillip |
September 27, 2001 |
Examining a diamond
Abstract
In order to test whether a diamond has had a layer a synthetic
diamond deposited thereon, the diamond is radiated with ultraviolet
radiation so as to form a pattern of beams of refracted and
reflected radiation, the pattern of refracted and reflected
radiation being observed on a screen behind the diamond.
Inventors: |
Smith, Martin Phillip;
(Wargrave, GB) |
Correspondence
Address: |
CESARI AND MCKENNA, LLP
88 BLACK FALCON AVENUE
BOSTON
MA
02210
US
|
Family ID: |
26307449 |
Appl. No.: |
09/766338 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09766338 |
Jan 19, 2001 |
|
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|
09011342 |
Mar 27, 1998 |
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Current U.S.
Class: |
250/372 ;
356/30 |
Current CPC
Class: |
G01N 21/87 20130101 |
Class at
Publication: |
250/372 ;
356/30 |
International
Class: |
G01N 021/87 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 1995 |
GB |
9515144.5 |
Claims
1. 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 the 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 beams of radiation substantially of wavelength substantially in
the range 230 nm to 320 nm.
2. A method according to claim 1 further comprising directing a
beam of ultraviolet radiation to a second face of the diamond and
observing the pattern of beams of radiation substantially of
wavelengths substantially in the range 230-320 nm produced by the
second surface and comparing the pattern of beams of the
first-mentioned face of the diamond and the second face of the
diamond.
3. A method according to claim 1 or 2, wherein a large number of
faces of the diamond are irradiated in succession.
4. A method according to any of claims 1 to 3, wherein the pattern
of reflected and refracted beams is observed by placing a screen a
predetermined distance from the diamond so that the beams of
refracted and reflected radiation impinge upon the screen and
detecting the pattern of beams on the screen.
5. A method according to claim 4, wherein an image of the screen is
formed.
6. A method according to claim 4 or 5, wherein the screen is placed
on the direction-of-irradiation side of the diamond, so that
back-scattered reflected and refracted beams are observed.
7. A method according to claim 4, 5 or 6, wherein the screen
comprises an ultraviolet sensitive fluorescent screen.
8. A method according to any preceding claim, further comprising
forming a reference image by irradiating the face of the diamond
with radiation which is substantially transmitted by all types of
diamond.
9. Apparatus for testing whether a diamond has had a layer of
synthetic diamond deposited thereon, comprising: means for
irradiating the diamond with ultraviolet radiation; a screen
mounted at a predetermined distance from the diamond so that the
screen intercepts a pattern of beams of reflected and refracted
radiation produced when a diamond is irradiated, and means for
allowing the pattern of beams of radiation substantially of
wavelength substantially in the range 230 nm to 320 nm on the
screen to be observed.
10. Apparatus according to claim 9, wherein the screen comprises an
ultraviolet fluorescent screen.
11. Apparatus according to claim 9 or 10, wherein the irradiating
means comprises a laser.
12. Apparatus according to any of claims 9 to 11, further
comprising means for irradiating the diamond with radiation which
is substantially transmitted by all types of diamond.
13. Apparatus according to any of claims 9 to 12, wherein the
screen is placed on the direction-of-irradiation side of the
diamond for intercepting back-scattered reflected and refracted
beams from the diamond.
14. A method of testing whether a diamond has had a layer of
synthetic diamond deposited thereon, substantially as herein
described with reference to the accompanying drawings.
15. Apparatus for testing whether a diamond has had a layer of
synthetic diamond deposited thereon, substantially as herein
described with reference to the accompanying drawings.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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/natural
diamond doublet".
[0006] 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/natural 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/natural diamond doublet.
[0007] 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. 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
[0008] 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.
[0009] 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.
[0010] 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 apparats is used and an expensive integrating sphere is not
required.
[0011] 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
[0012] The present invention provides a method of testing whether a
diamond has had a layer of synthetic diamond deposited thereon,
comprising:
[0013] 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
[0014] 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.
[0015] 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
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] Preferably, substantially the whole of the presented face of
the diamond is irradiated. This allows a complete pattern of beams
to be formed and observed.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] The beam of irradiating radiation may be of size less than
the presented face of the diamond but is preferably greater in
size.
[0026] 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.
[0027] Preferably, the pattern of reflected and refracted beams is
observed by placing a screen a predetermined distance from the
diamond so that the beams of reflected and refracted radiation
impinge upon the screen, and detecting the pattern on the screen.
Preferably an image of the pattern on the screen is formed. The
screen may be movable and angularly adjustable with respect to the
diamond.
[0028] The screen is particularly preferably placed on the
direction-of-irradiation side of the diamond, so that
back-scattered reflected and refracted beams are observed. In this
case, it is preferable that the irradiating radiation passes to the
diamond through an aperture in the screen.
[0029] The screen may comprise an ultraviolet sensitive fluorescent
screen for revealing the pattern of beams produced. In this case,
the screen may be observed by eye through an observing means having
a filter for cutting out hazardous irradiating radiation.
[0030] Alternatively, a camera may be used to observe the
screen.
[0031] The radiation observed could comprise a narrow band of
wavelengths lying substantially in the above mentioned range, a
number of such narrow bands or it could be a relatively broad band.
Optionally, it falls substantially in the range 230 nm to 300 nm,
being preferably below 290 nm. The radiation observed may comprise
some radiation of wavelength falling outside the range 230 nm to
320 nm but such radiation is preferably of sufficiently low
intensity to avoid confusing the beams observed at the wavelength
of interest.
[0032] The radiation may be generated by a suitable laser, e.g. a
248 nm krypton fluoride excimer laser.
[0033] In order to observe radiation substantially of wavelength
substantially 230 nm to 320 nm, the diamond may be irradiated only
with such radiation (produced by a laser or by a wider band source
having a filter). Alternatively, the diamond may be irradiated with
radiation of a broader range of wavelengths, wavelength selective
means such as a filter being provided between the diamond and the
screen or imaging means to pass radiation of wavelength
substantially 230 nm to 320 nm. If the diamond is irradiated with
radiation substantially of wavelength substantially 230 nm to 320
nm, wavelength selective means may also be provided to exclude
radiation produced by fluorescence excited by the incident
ultraviolet radiation. Normally, however, the intensity of
fluorescence is not strong enough to require filtering.
[0034] When the irradiating radiation is incident on a zone of the
diamond, it will generally be strongly absorbed or partially
transmitted. The radiation transmitted by a zone of the diamond
will be refracted inside the diamond and some transmitted radiation
may be observed leaving the surface of the diamond. Thus, a pattern
of beams of reflected and refracted radiation will be produced when
a face of a diamond is irradiated.
[0035] The intensity of reflected beams from any given surface will
depend in part upon the transmissivity of that surface and in part
upon the angle of incidence of the radiation upon the surface. The
intensity of refracted radiation beams will depend in part upon the
transmissivity of the diamond material of a part observed and in
part on its thickness.
[0036] Natural diamond usually has such a high absorption
coefficient at the wavelengths in question that incident radiation
is almost totally absorbed.
[0037] CVD or other synthetic diamond material surface layers are
commonly of a type that at least partially transmits the radiation,
in particular type II diamond.
[0038] Thus, where a face of a diamond is irradiated normally and
substantially no refracted beams are produced other than the
reflection normal to the face, it may be concluded that the face is
probably natural diamond.
[0039] Where a face is normally irradiated and a pattern of weak
reflected and refracted beams is observed, the presence of a thin
layer of synthetic diamond is indicated.
[0040] Where a face of a diamond is irradiated at a relatively
large angle off the normal (referred to as "oblique irradiation"),
and a relatively weak and simple pattern of reflected beams is
produced, it may be concluded that the face irradiated comprises
natural diamond. If, however, a pattern of relatively strong and
complex reflected and refracted beams is observed, the presence of
synthetic diamond material is suggested.
[0041] Any suggestion of synthetic diamond material should be
followed up with further testing, as the reflected and refracted
beams may be due to natural diamond of a rare type.
[0042] If a diamond is irradiated on a face which is substantially
symmetrical, and a pattern which is grossly unsymmetrical (for
example, light on one side, dark on the other) is produced, it may
be concluded that the sides of the face of the diamond presented
are of different composition.
[0043] Because of the complex pattern of light paths within a
brilliant-cut diamond, the two parts of a CVD/natural diamond
doublet may not be immediately apparent. It may be necessary to
manipulate a CVD/natural diamond doublet while it is being viewed,
in order to clearly see the two parts of the diamond.
[0044] In order to assist in the interpretation of the patterns of
reflected and refracted beams produced when a diamond is irradiated
with the first mentioned radiation, the diamond may be irradiated
with radiation which is substantially transmitted by all types of
diamond, such as visible radiation, so that a reference pattern may
be formed. This pattern may then be compared to a pattern obtained
using the first mentioned radiation, preferably with the diamond in
the same configuration.
[0045] The reference pattern is expected to show relatively strong
and complex patterns of reflected and refracted radiation for all
types of diamond.
[0046] The present invention further provides apparatus for testing
whether a diamond has had a layer of synthetic diamond deposited
thereon, comprising means for irradiating the diamond with
ultraviolet radiation, and
[0047] a screen mounted a predetermined distance from the diamond
so that the screen intercepts a pattern of beams of reflected and
refracted radiation produced when a diamond is irradiated, and
[0048] means for allowing the pattern of beams of radiation
substantially of wavelength substantially in the range 230 nm to
320 nm on the screen to be observed
[0049] The apparatus according to the invention could be automated
to automatically interpret and analyze images or readings produced.
However, this is not preferred as a simple system in which the
images are interpreted by the operator is practicable and
cheaper.
[0050] The invention will be further described by way of example
only, with reference to the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIG. 1 is a schematic illustration of apparatus according to
the invention; and
[0052] FIGS. 2a-2f are schematic illustrations of patterns of
reflected and refracted beams produced according to the present
invention when various diamonds are irradiated with ultraviolet or
visible radiation.
DETAILED DESCRIPTION OF THE DRAWINGS
[0053] In the apparatus shown schematically as 1 in FIG. 1, a
diamond 2 is irradiated with ration of wavelength substantially in
the range 230-320 nm by a laser 3. The laser beam 4 is directed
through a screen 5, through an aperture 6 provided in the middle
thereof. When the beam of radiation 4 is incident upon the diamond
2, a pattern of beams of reflected and refracted radiation may be
produced. The pattern produced in the back-scattered direction is
studied in the embodiment shown in FIG. 1 The screen 5 is movable
and angularly adjustable. The pattern is studied by arranging the
screen 5 at a distance from the diamond 2 such that substantially
all the beams of reflected and refracted radiation are intercepted
by the screen. Typically, for a screen of size 100 mm.times.100 mm,
the distance between the diamond and the screen is circa 60 mm.
[0054] An observing means 7 is provided for observing the pattern
of reflected and refracted beams formed on the screen 5.
[0055] The screen 5 is a UV fluorescent screen, which generates
spots of visible light where ultraviolet radiation of wavelength
230-320 nm is incident upon it. The observing means 7 may comprise
a suitable optical device with a filter for filtering out radiation
of ultraviolet wavelengths, which can be dangerous to the eye.
[0056] The whole apparatus 1, except for the observing means 7 may
be enclosed in a light-tight box, for excluding external radiation
which may confuse the pattern on the screen and for containing the
dangerous UV radiation. The observing means 7 may be mounted at a
suitable position within the walls of the light-tight box so that
an observer can see the pattern on the screen 5.
[0057] In order to provide a reference pattern, a laser 8 producing
light of a visible wavelength is provided. A beam splitter 9 is
provided in the path of beam 4 so that the visible radiation from
laser 8 may be directed down the path of the irradiating radiation
4 from laser 3. Preferably, lasers 3 and 8 are used in alternation
so that the different patterns produced by the different types of
radiation may be compared.
[0058] In FIGS. 2a to 2f the results of irradiation of a diamond
according to the invention are shown.
[0059] Three cases were studied:
[0060] a. A diamond which is a CVD/natural diamond doublet, with
the synthetic part on the culet of the diamond,
[0061] b. A CVD/natural diamond doublet in which the synthetic
diamond is formed on the table of the diamond,
[0062] c. A completely natural diamond
[0063] In each case, the diamond is a cut diamond having a
brilliant cut, being the type of cut which will be most frequently
encountered. The technique is, however, applicable to all diamond
cuts, including fancy cuts, although a more complex and careful
interpretation of the returned pattern may be required for fancy
cuts.
[0064] The diamond is irradiated using the three steps:
[0065] 1 irradiation of the table in a normal direction using
ultraviolet radiation of wavelength substantially in the range
230-320 nm,
[0066] 2 normal irradiation of the table using visible radiation,
and
[0067] 3 irradiation of the culet using ultraviolet radiation
substantially of wavelength falling in the range substantially
230-320 nm.
[0068] The above-mentioned three types of diamond can be
distinguished by the different patterns of reflected and refracted
radiation that they produce.
[0069] In FIGS. 2a-2f, spots of high intensity are shown as a solid
black dot, spots of medium intensity are shown as short complete
lines and spots of low intensity are shown as short, dotted
lines.
[0070] FIGS. 2a-2c, the results of steps 1 and 2 are shown on a
single screen for comparison, though in practice they would be
separate.
[0071] FIG. 2a shows the results of steps 1 and 2 with diamond
(a).
[0072] The pattern on the screen in step 1 is observed to comprise
a single high intensity spot 10 produced by normal rejection of the
irradiating radiation.
[0073] In step 2, a complex relatively intense pattern of spots 11
is observed.
[0074] FIG. 2b shows the results of steps 1 and 2 with diamond (b)
In step 1, a pattern of reflected and refracted beams 12 of
relatively low intensity is observed. In step 2, a pattern of
reflected and refracted beams of relatively high intensity is
produced. The patterns are different, as the refractive index of
diamond at the ultraviolet wavelengths observed is different to the
refractive index of visible radiation.
[0075] FIG. 2c shows the results of steps 1 and 2 with diamond (c).
In step 1 a single relatively high intensity spot 14 is produced by
normally reflected radiation only. In step 2, a relatively intense
and complex pattern of reflected and refracted beams 15 is
produced. The patterns observed in FIG. 2c are similar to those
shown in FIG. 2a.
[0076] FIG. 2d shows the results of step 3 with the diamond (a). A
relatively complex pattern of strong reflected and refracted beams
17 is produced, together with a strong beam 16 due to radiation
reflected normally from the culet (assuming that there is a culet
facet).
[0077] FIG. 2e shows the results of step 3 with diamond (b). A
relatively weak simple pattern of reflected beams 18 is produced
due to reflection off the cut surfaces around the culet.
[0078] FIG. 2f shows the results of step 3 with diamond (c). A
simple pattern of relatively weak reflected beams 19 is
produced.
[0079] In the apparatus shown in FIG. 1, the ultraviolet laser may
comprise a 248 nm krypton fluoride excimer laser from Potomac
lasers. The laser 8 may comprise a 635 nm laser diode or 633 nm
HeNe laser from Vector Technology/Melles Griot. The beam splitter 9
is manufactured by Spindler and Hoyer and the ultraviolet sensitive
fluorescent screen is supplied by Levy-Hill Ltd. If a camera is
used to observe the screen 5, it may be a CCD camera coupled to a
computer for analysing the spot pattern produced.
* * * * *