Determination of gemstone composition
By using the Sabinoscope tomography technique, the axial contour of the cold-light-generated gemstone is captured by the excitation beam and tilt angle, which solves the problem of the difficulty in identifying synthetic materials in gemstones in the existing technology and enables accurate detection of imitations.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DE BEERS UK LTD
- Filing Date
- 2021-01-06
- Publication Date
- 2026-05-19
AI Technical Summary
Existing technologies are insufficient to effectively identify the presence of synthetic materials in gemstones, especially in imitations, particularly in the case of colorless diamonds, where traditional screening methods cannot accurately detect the presence of synthetic materials.
Using the Saxometry tomography technique, the excitation beam passes through the gemstone essentially from its table to its tip, and the cold light emitted by the gemstone is captured at an angle to generate the axial profile of the gemstone. Discontinuities are then identified to determine whether the gemstone is a replica.
It can accurately identify the presence of synthetic materials in gemstones, is suitable for inlaid gemstones, and improves the accuracy and efficiency of counterfeit detection.
Smart Images
Figure CN115210558B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for determining the composition of polished gemstones. In particular, the method relates to determining whether a polished gemstone is a counterfeit. Background Technology
[0002] A major problem in the gemstone (especially diamond) industry is the existence of undisclosed synthetics, including hybrid stones and imitations. Imitations are essentially synthetic stones grown onto or otherwise attached to natural cut stones. For example, such as... Figure 1a and Figure 1b As shown, the natural stone pavilion 10 (in this case, the chemical vapor deposition (CVD) crown 12) can be enhanced by adding synthetic stone to form a composite or imitation 14. Besides the combination of a natural pavilion and a synthetic crown, as... Figure 1b As shown, imitations can also be composed of a natural crown and a synthetic pavilion. Figure 1c The diagram further illustrates the various elements of a cut gemstone (table, crown, girdle, pavilion, culet). Typically, the distance from the table to the girdle of a brilliant-cut gemstone is approximately 25% of the total depth of the stone or gem.
[0003] Natural stones can be enhanced by altering their color (e.g., by adding a boron-doped synthetic layer to make a colorless natural stone appear blue) or by causing a price surge (e.g., by increasing the weight of the natural stone to 0.5 or 1 carat). Imitations involving synthetic CVD with an overgrowth thickness of 740 micrometers have been reported.
[0004] The ability to identify diamonds (which are purely synthetic) has been primarily achieved through the development of deep UV imaging instruments such as DiamondView. TM and SynthDetect TM This can be addressed through knowledge of the markings of natural diamonds. However, identifying imitations presents a greater challenge, as they may pass initial screening and therefore may never be used for reference testing by more advanced screening instruments. In particular, while fancy colored (e.g., blue) stones or gemstones may be referenced by DiamondView for further testing, this is unlikely to occur with colorless stones or gemstones.
[0005] Therefore, there is a need to develop an effective screening method for imitations (especially type IIa / IaAB diamonds). Preferably, this screening will detect synthetic materials present in the crown or pavilion of the stone or gemstone, and is applicable to loosely set stones or gemstones. Summary of the Invention
[0006] In one aspect of the invention, a method for determining the composition of a polished gemstone is provided. The method includes: passing an excitation beam through the gemstone substantially from its table to its apex, the axis of the excitation beam being substantially perpendicular to the table; and capturing cold light emitted by the gemstone at an angle inclined to the axis of the excitation beam.
[0007] Cold light can be captured in the image capture plane by tilting it at a first angle relative to the optical axis extending from the table of the gemstone to the image capture plane. The tilt angle can optionally be about 60° or 50°.
[0008] This method may include generating an axial profile that produces the cold light properties of a gemstone.
[0009] The method may include determining whether the axial profile includes one or more discontinuities, wherein if a discontinuity is present, the gemstone is identified as a counterfeit.
[0010] This method may include capturing cold light as the gemstone is moved laterally relative to the beam.
[0011] The excitation beam may include a light plate.
[0012] The excitation beam can have a wavelength of approximately 532 nm. Alternatively, the excitation beam can have a wavelength of approximately 405 nm.
[0013] The emitted cold light can be fluorescence. Alternatively, the emitted cold light can be phosphorescence.
[0014] Gemstones can be diamonds. Gemstones can be set in jewelry or similar objects.
[0015] According to another aspect of the invention, a method is provided for determining whether a polished gemstone is a counterfeit. The method includes: exciting the gemstone to produce cold light; capturing the cold light at an angle tilted to the excitation axis; generating an axial cold light profile of the gemstone; and identifying the gemstone as a counterfeit if the profile includes one or more discontinuities.
[0016] According to another aspect of the invention, an apparatus for determining the composition of a polished gemstone is provided. The apparatus includes: an excitation source configured to irradiate the gemstone with an excitation beam via the table of the gemstone; and a capturing device configured to capture cold light emitted by the gemstone at an angle inclined to the axis of the excitation beam.
[0017] The device may include a focusing system configured to focus the cold light emitted by the gemstone to produce an image at the capturing device.
[0018] The image capture plane of the capturing device can form a first angle with the optical axis of the focusing system. This first angle can be substantially equal to and opposite to a second angle between the optical axis and the axis of the excitation beam.
[0019] A focusing system may include one or more lenses.
[0020] The device may include a lens configured to focus the excitation beam.
[0021] The device may include means configured to move a gemstone relative to an excitation beam.
[0022] The device may include a processor coupled to the capturing device and configured to generate an axial profile of the cold light properties of the gemstone.
[0023] The image capture plane, optical axis, focusing system, and excitation beam can be configured to enable Scheimpflug tomography.
[0024] The device may include a processor configured to convert cold light captured by the capturing device into an image, search for discontinuities in the image, and, in the presence of such discontinuities, determine that the gemstone is a counterfeit. Attached Figure Description
[0025] Figure 1a Natural cut gemstones are shown;
[0026] Figure 1b Counterfeit products were shown;
[0027] Figure 1c It shows aspects of gemstone cutting;
[0028] Figure 2 This is a schematic diagram of an apparatus used to determine the composition of polished gemstones;
[0029] Figure 3 The optical conditions to be met are shown;
[0030] Figure 4a and Figure 4b The cool-light profile of the first gemstone is shown;
[0031] Figure 5a and Figure 5b The cool-light profile of the second gemstone is shown; and
[0032] Figure 6 Tomographic scans of other gemstones are shown. Detailed Implementation
[0033] This paper describes a method for determining the composition of a polished gemstone using Sabinoscope tomography (i.e., segmented gemstone imaging). The method involves passing an excitation beam through the polished gemstone substantially downwards from the table to the culet, and capturing the cold light emitted by the gemstone at an angle tilted to the axis of the excitation beam. The captured cold light can be used to generate an axial cross-section of the gemstone's luminescent properties.
[0034] The wavelength of the excitation beam can be selected to produce cold light (i.e., fluorescence) based on different point defects in the gemstone (e.g., N3 centers (three nitrogen atoms surrounding a vacancy) and / or NV-centers (a substituted nitrogen atom adjacent to a vacancy)). In a non-limiting example, the excitation beam can have a wavelength of approximately 532 nanometers (nm). This beam can be provided by a green laser, which can be used to excite centers in any CVD material expected to be present within the gemstone. In another non-limiting example, a violet laser (with a wavelength of approximately 360 nm–480 nm, and preferably less than 415 nm, e.g., 405 nm) can be used to excite N3 defects present in most natural diamonds. Optionally or additionally, two-color cold light tomography can be used to obtain one or more images of the stone or gemstone.
[0035] According to the Shaper principle, any cold light produced by the excitation beam is captured at an angle (i.e. off-axis) to the direction of the beam, where the irradiation plane and the image plane are tilted relative to each other.
[0036] The Saxophone technique, utilizing light sheets, is known in corneal photography and fluorescence microscopy. A laser sheet comprises a beam of light focused in only one direction using a lens. Advantages of the Saxophone technique can include: speed (in terms of photon efficiency, since the light is only in the focal plane); multi-channel capability (suitable for multispectral imaging); and cost (CMOS camera technology can be used to acquire images).
[0037] The Saxophone technique has an additional advantage in this respect because imaging of mounted gemstones is feasible, as the stone or gemstone is "scanned" from above, from the table down to the pavilion, by a beam of light or a plate of light. It will be understood that light is not directly collected through the facets of a cut and polished gemstone (such as a diamond), and when the gemstone is set in jewelry (e.g., a ring, necklace, watch, etc.), the pavilion is typically inaccessible, making it impossible to directly collect light through the facets of the cut and polished gemstone.
[0038] It will be understood that very short wavelengths of light (below approximately 225 nm) are strongly absorbed by diamonds and therefore will not penetrate the stone or gemstone. Therefore, longer wavelengths of excitation are required so that the beam or sheet of light can penetrate the stone or gemstone.
[0039] Figure 2An exemplary apparatus 100 for performing the method described above for determining the composition of a polished gemstone 110 is shown. Apparatus 100 includes a light source 120 configured (in this example) to generate a light beam (e.g., a 10mW, 532nm Gaussian beam) 130, which can be focused using a first lens 140. Apparatus 100 also includes a capture device 150 (e.g., a CMOS device or sensor) configured to capture an image of the cold light generated by the gemstone 110 via a pair of objectives 160 (e.g., back-to-back 10x0.3NA objectives that collect light from the gemstone and focus the light to produce an image at capture device 150). Optionally, apparatus 100 may include a processor 170 linked to capture device 150. Optionally or additionally, apparatus 100 may include a dual-wavelength irradiation element.
[0040] like Figure 2 As shown, the pair of objective lenses 160 produce an image of the gemstone 110 at the capturing device 150. The optical axis O is at an angle to the beam axis B. The image plane I forms a similar but opposite angle to the optical axis. This follows the Shaper principle, in which:
[0041] , where M = magnification.
[0042] exist Figure 2 In the unrestricted example, M = x1, and The beam waist (i.e., the beam size at its focal point) is approximately F#16 (i.e., approximately 16 μm). Due to the 60-degree angle, the z-resolution is 54 μm, and the gemstone's refractive index is n = 2.4. At a 60-degree angle, approximately 2 / 3 of the gemstone's depth from the table downwards can be imaged. For full-depth imaging from the table to the cusp, the angle (i.e., the z-resolution is 54 μm) is... , The temperature is approximately 50 degrees.
[0043] Typically, known microscope and camera lenses are designed to closely follow the well-known Abbe sine condition, and thus produce lateral 2D images close to the diffraction limit. (Reference) Figure 3 The Abbe sine condition is as follows:
[0044] y0n0sinγ0=y1n1sinγ1 where n0 and n1 refer to the immersion medium of the object and the image (in fact, both are air).
[0045] However, in order to produce a similar aberration-free image along the optical axis of the lens, the Hershel condition must also be satisfied:
[0046] z0n0sin(γ0 / 2)2 =z1n1sin(γ1 / 2) 2
[0047] For the two conditions to be satisfied, the magnification requirement is n. image / n object And the magnification must satisfy:
[0048] γ0=γ1
[0049] Therefore, the magnification of the image is set to 1 (i.e., M = x1), but it is actually reduced by the refractive index of the gemstone (n = 2.4). In other words, the apparent depth scales the outline of the capturing device by 1 / n = 1 / 2.4.
[0050] For a dry target (i.e., operated by air), the magnification (m) = 1, and m = y1 / y0 = z1 / z0 = n0 / n1.
[0051] The aforementioned device 100 generates an image of the axial profile of the jewel 110 as a function of its light-emitting properties and represents the material composition of the jewel 110. In this way, different material layers within the jewel 110 can be identified.
[0052] Initial alignment of the gemstone 110 with the components of the device 100 can be determined by the bright field of view reflected by optical imaging and the position of the rear and front parts of the stone or gemstone. Perpendicular alignment of the gemstone 110's table facet with the beam axis can be achieved by reflecting the beam from the gemstone 110's table facet back to a quadrant diode, or by using a similar method. Alignment of the gemstone 110 may be necessary to accurately determine the source of any detected cold light.
[0053] Figure 4a The image shows the cold light profile / single depth profile of a stone or gemstone captured by device 100 under excitation at approximately 532 nm, illustrating the spatial distribution of cold light (fluorescence) in a 1.3-carat first diamond gemstone acquired at a time of 16 ms. This distribution indicates a difference or discontinuity in the cold light properties of the gemstone's table (crown) and pavilion, with the crown exhibiting a greater degree of cold light (fluorescence) than the pavilion. This variation in cold light properties from the table to the pavilion indicates that the imaged gemstone is a replica, in this case including both a CVD table of standard purity and a pavilion of natural diamond.
[0054] Figure 4b The diagram shows... Figure 4a The gemstone's axial cool light profile from the table to the pavilion.
[0055] Figure 5aThe image shows the cold light profile / single depth profile of a stone or gemstone captured by device 100 under 532 nm excitation, illustrating the spatial distribution of cold light (fluorescence) in a second diamond gemstone acquired at a time of 16 ms. This distribution indicates a difference or discontinuity in the cold light properties of the crown and pavilion of the gemstone, with the pavilion exhibiting a greater degree of cold light (fluorescence) than the crown. This variation in cold light properties from the table to the pavilion suggests that the imaged gemstone is a replica, in this case including CVD-synthetic pavilions of standard purity and HPHT (high pressure, high temperature) synthetic crowns.
[0056] Figure 5b The diagram shows... Figure 5a The gemstone's axial cool light profile from the table to the pavilion.
[0057] A 2D tomographic scan (i.e., slice) of gemstone 110 can be obtained via beam scanning, generation by a light sheet, movement of the gemstone relative to the beam / light sheet, or a combination thereof. To achieve this, the aforementioned device 100 may include an x, y, z manipulation device (not shown here) that laterally moves the stone or gemstone relative to the beam. Optionally, this device may be used to pass the beam through a stationary stone or gemstone. It is necessary to scan two dimensions using a beam and scan one dimension using a light sheet.
[0058] exist Figure 6 The image shows cross-sectional scans of other diamond gemstones with CVD crowns and natural pavilions. (Compared to the image above...) Figure 4a and Figure 5a The cold light contour shown is the opposite. Figure 6 The outline is generated via beam scanning (i.e., moving the beam laterally along a line parallel to the table of the gemstone). This produces an image of a cold light from a “slice” of the stone or gemstone produced under excitation. The same result can be achieved by using a laser sheet instead of beam scanning. As shown, the gemstone includes a CVD (synthetic) crown that fluoresces under excitation and a natural pavilion that does not.
[0059] therefore, Figure 6 The tomographic scan shown reveals discontinuities in the gemstone's luminescence properties, indicating that the gemstone comprises layers of different materials (in other words, the gemstone is non-homogeneous and formed from two or more different materials). The boundary or interface between the luminescent / non-luminescent regions of the stone or gemstone is substantially parallel to the table. This interface can be located in the pavilion, girdle, or crown.
[0060] Optionally, a complete 3D image and / or model of the gemstone can be obtained by rotating the gemstone 110 around its central axis for use in slice illumination or in single-point illumination that synchronizes beam scanning and objectives. Once multiple 2D images of the stone or gemstone have been obtained (optionally using multiple image capture devices), these 2D images can be combined using a processor to generate a 3D model of the stone or gemstone. Optionally or additionally, the processor can perform image processing on the obtained 2D images to clean and / or highlight areas of the image, and / or fit the image shape to the known shape of the gemstone.
[0061] As used herein, fluorescence is a type of cold light characterized as being produced only when excited. Phosphorescence is a type of cold light that is retained but decays once the excitation is removed.
[0062] As used herein, "natural" is defined as a stone that is derived from nature and consists solely of diamond-like components produced through geological processes. As defined herein, the term "natural" indicates that the stone is not synthetic, but does not exclude the possibility that the stone may have been treated, for example, by pressure or heat treatment, unless otherwise specified.
[0063] As used herein, synthesis is defined as a man-made material consisting solely of diamond (diamond) components produced through artificial or industrial processes such as chemical vapor deposition or high-pressure, high-temperature processes.
[0064] As used herein, treatment is defined as modifying a natural material (as defined above) by means of chemical or mechanical means, by irradiation, or by pressure or heat treatment in order to improve its color or transparency.
Claims
1. A method for determining the composition of a polished gemstone, the method comprising: An excitation beam is directed through the gemstone from its table to its tip, with the axis of the excitation beam perpendicular to the table. The cold light emitted by the gemstone is captured by tilting at an angle to the axis of the excitation beam. The cold light is captured in the image capture plane at a first angle inclined to the optical axis extending from the table of the gemstone to the image capture plane. The first angle is equal to and opposite to the second angle between the optical axis and the axis of the excitation beam.
2. The method of claim 1, further comprising generating an axial profile of the luminescent properties of the gemstone.
3. The method of claim 2, further comprising determining whether the axial profile includes one or more discontinuities, wherein in the presence of discontinuities, the gemstone is identified as a counterfeit.
4. The method according to any one of claims 1-3, comprising capturing cold light while moving the gemstone laterally relative to the light beam.
5. The method according to any one of claims 1-3, wherein, The excitation beam includes a light plate.
6. The method according to any one of claims 1-3, wherein, The excitation beam has a wavelength of 532 nm.
7. The method according to any one of claims 1 to 3, wherein, The excitation beam has a wavelength of 405 nm.
8. The method according to any one of claims 1-3, wherein, The emitted cold light is fluorescence.
9. The method according to any one of claims 1-3, wherein, The gemstone in question is a diamond.
10. The method according to any one of claims 1-3, wherein, The gemstone is set in jewelry or the like.
11. An apparatus for determining the composition of a polished gemstone, the apparatus comprising: An excitation source is configured to irradiate the gemstone with an excitation beam passing through the table of the gemstone and reaching the apex of the gemstone, with the axis of the excitation beam perpendicular to the table of the gemstone. A capturing device configured to capture the cold light emitted by the gemstone at an angle inclined to the axis of the excitation beam, and A focusing system configured to focus the cold light emitted by the gemstone to produce an image at the capturing device. Wherein, the image capture plane of the capturing device forms a first angle with the optical axis of the focusing system; and The first angle is equal to and opposite to the second angle between the optical axis and the axis of the excitation beam.
12. The device according to claim 11, wherein, The focusing system includes one or more lenses.
13. The device of claim 11, further comprising a lens configured to focus the excitation beam.
14. The apparatus of claim 11, further comprising means configured to move the gemstone relative to the excitation beam.
15. The device according to any one of claims 11 to 14, comprising a processor coupled to the capturing device and configured to generate an axial profile of the luminescent properties of the gemstone.
16. The device according to any one of claims 11 to 14, wherein, The image capture plane, optical axis, focusing system, and excitation beam are configured to enable Sabinometric tomography.
17. The device according to any one of claims 11 to 14, further comprising a processor configured to convert the cold light captured by the capturing device into an image, search for discontinuities in the image, and, in the presence of such discontinuities, determine that the gemstone is a counterfeit.