Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B44—DECORATIVE ARTS
  • B44B—MACHINES, APPARATUS OR TOOLS FOR ARTISTIC WORK, e.g. FOR SCULPTURING, GUILLOCHING, CARVING, BRANDING, INLAYING
  • B44B7/00—Machines, apparatus or hand tools for branding, e.g. using radiant energy such as laser beams
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B44—DECORATIVE ARTS
  • B44B—MACHINES, APPARATUS OR TOOLS FOR ARTISTIC WORK, e.g. FOR SCULPTURING, GUILLOCHING, CARVING, BRANDING, INLAYING
  • B44B3/00—Artist's machines or apparatus equipped with tools or work holders moving or able to be controlled substantially two- dimensionally for carving, engraving, or guilloching shallow ornamenting or markings
  • B44B3/04—Artist's machines or apparatus equipped with tools or work holders moving or able to be controlled substantially two- dimensionally for carving, engraving, or guilloching shallow ornamenting or markings wherein non-plane surfaces are worked
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B44—DECORATIVE ARTS
  • B44B—MACHINES, APPARATUS OR TOOLS FOR ARTISTIC WORK, e.g. FOR SCULPTURING, GUILLOCHING, CARVING, BRANDING, INLAYING
  • B44B2700/00—Machines, apparatus, tools or accessories for artistic work
  • B44B2700/08—Machines, apparatus or hand tools for branding

Definitions

• the present invention relates to a method and apparatus for marking a surface of a diamond or other gemstone.
• the mark may be any mark, but the invention is particularly but not exclusively directed to applying an information mark to the diamond.
• the diamond may be, for instance, an industrial diamond such as a wiredrawing die, though the invention is of particular interest in marking gemstone diamonds, and especially for applying a mark which is invisible to the naked eye or invisible to the eye using a xlO loupe (which is the loupe used by jewellers), when the mark can be applied to a polished facet of the gemstone without detracting from its clarity grade.
• the marks can be used to uniquely identify the gemstone by a serial number or as a brand or quality mark, but it should not detract from the value or appearance of the stone, and should preferably not exhibit blackening.
• a method of forming a mark on the surface of a diamond or gemstone comprising the step of forming a plurality of grooves on the surface of the diamond or gemstone, the mark being such that it cannot be read by the naked eye, the grooves producing a visible diffraction effect under certain predetermined lighting conditions, such that the mark can be read under certain predetermined magnification conditions.
• an apparatus for performing the above-mentioned method comprising: a diamond or gemstone which has been marked by the above-mentioned method.
• a method of forming a mark on the surface of a diamond or gemstone comprising the step of forming a plurality of grooves on the surface of the diamond, said grooves producing a visible diffraction effect under certain predetermined illumination conditions without detrimentally affecting the clarity grade of the diamond or gemstone.
• an apparatus for performing the above-mentioned method comprising: a diamond or gemstone which has been marked by the above-mentioned method.
• each groove is not less than about 10 nm deep and/or not more than about 50 nm deep with no evidence of blackening. A specific example would be around 30 nm.
• the grooves may be in the form of parallel lines, or even a plurality of intersecting grooves forming cross-hatched pattern, depending on the effect desired.
• marking can be carried out using any suitable means, e.g. etching with an excimer laser or plasma etching, marking is preferably carried out using an ion beam, and most preferably by direct writing on the diamond surface with a focused ion beam.
• etching with an excimer laser or plasma etching marking is preferably carried out using an ion beam, and most preferably by direct writing on the diamond surface with a focused ion beam.
• ion beam By limiting the dose, sputtering of carbon atoms can be avoided, sputtering causing direct material removal; this enables a mark to be applied with a controlled depth and good resolution.
• Gallium ions are used, but a beam of other suitable ions may alternatively be used.
• the incident ions cause disordering that converts the diamond to a graphite-like or other non-diamond structure that can be cleaned using, for example, a powerful oxidizing agent, such as molten potassium nitrate, at a temperature of approximately 380-550 Centigrade for a period of between a few minutes and several hours.
• a powerful oxidizing agent such as molten potassium nitrate
• potassium nitrate has been found to be more effective in removing disordered diamond than other known processes, thus allowing a mark of a given depth to be produced with a relatively low dose of ions.
• Suitable oxidising agents may be molten compounds such as alkali metal salts; compounds in the form XnYm where the group X may be Li + , Na + , K + , Rb + , Cs + or other cation, and the group Y may be OH " , NO 3 " , O 2 2 ⁇ O 2 ⁇ CO 3 " or other anion, the integers n and m being used to maintain charge balance. Mixtures of such compounds may be used. Air or other oxygen-containing gases may also be present.
• the disordered layer of the diamond can be removed using an acid or potassium nitrate dissolved in acid.
• an acid or potassium nitrate dissolved in acid for example, molten potassium nitrate eliminates acid fumes.
• the need to dispose of spent acid is eliminated, thereby offering safety, environmental and economic benefits.
• the depth of disordering is determined by the range of ions. For 50 keV Gallium, this range is about 30 nm.
• the minimum dose may be around 10 13 / cm 2 and is preferably about 10 14 /cm 2 to 10 15 /cm 2 , but good marks can be applied with a fairly modest dose, the preferred maximum dose being about 10 /cm or even up to about 10 /cm . However, the dose depends upon the ions being used and their energy (as measured in keV).
• the ion beam dose is a total number of incident ions per unit area at the sample surface, during the marking.
• the beam current may be about 0.5 nA, and the beam energy not less than about 10 keV or about 30 keN and/or not greater than about 100 keV or about 50 keV.
• the region to be marked and/or the surrounding area may be coated with an electrically conducting layer, for instance gold, prior to forming the mark, so that an electrical connection can be provided before marking with an ion beam, to prevent charging.
• the thickness of the gold, or other coating alters the variation of depth of the mark with beam energy and may thus be chosen to optimise the mark produced.
• the accuracy of the method is such that no masking is required: the ion beam is applied directly to the surface of the diamond at the positions where the grooves are required to be formed.
• the ion beam is applied directly to the surface of the diamond at the positions where the grooves are required to be formed.
• an apparatus for viewing a mark formed on a diamond using the method of the first or second aspect of the present invention comprising illumination means for illuminating the mark with directional light at an angle which corresponds to the diffraction angle of light of a predetermined wavelength or band of wavelengths, viewing means for viewing said mark, and magnification means for magnifying the viewed image of said mark.
• the invention also extends to a method of viewing the mark corresponding to the apparatus defined above.
• the mark is preferably viewed against a dark background, ie. it is preferred that the illuminating light is substantially prevented from reflecting through the stone and appearing directly behind or close to the mark. It will be apparent to a person skilled in the art that, in order to achieve this, the angle and direction from which the illuminating light is supplied (and hence the orientation and spacing of the lines) must be chosen so as to ensure that no light can follow the undesired path.
• the typical range of magnification required to view the mark is xlO to x50.
• n is an integer.
• d is the distance between each groove
• ⁇ is the angle of the incident light
• ⁇ is the wavelength of the diffracted light
• n is an integer.
• n l.
• d and n are fixed, and the wavelength of diffracted light, i.e. the colour which the mark will appear when viewed, can be varied by varying the angle of incident light.
• the angle of the incident light i.e. ⁇
• ⁇ is set so that ⁇ is around 450nm, using the above equation.
• ⁇ is set so that ⁇ is around 620nm.
• the illuminating means may comprise a light source and an opaque screen located in the incident light path, the screen having two apertures formed therein, the apertures being formed on either side of a generally central position such that two angular directional light sources are produced. The distance between the apertures determines the angle of the incident light sources.
• the directional light source(s) may be provided by any convenient means, e.g. two separate light sources.
• a conventional microscope may include illumination means comprising a circular ring-shaped source comprising optical fibres illuminated by a remote tungsten light bulb. The illumination means of the present invention can be obtained by masking off all but two diametrically opposite sections of the illuminator.
• Figure 1 is a magnified schematic diagram of the type of mark which is formed using the method and apparatus of the first and second aspects of the present invention
• Figure 2 is a further magnified cross-sectional view along line A - A of Figure 1;
• Figure 3 is a schematic view of an embodiment of apparatus according to the third aspect of the present invention.
• a mark in the form of an alphanumeric character may be formed by means of a plurality of equally spaced, parallel elongate grooves 10 each separated by a distance d.
• Each groove 10 may have a generally square or rectangular cross-section, as shown in Figure 2.
• a sinusoidal profile may be preferred to reduce unwanted higher order diffraction.
• a diamond gemstone is mounted in a suitable holder and placed in a vacuum chamber equipped with a focused ion beam source such as supplied by FEI or Micrion.
• a focused ion beam source such as supplied by FEI or Micrion.
• the region to be marked may be irradiated using an electron flood gun supplied by Micrion, providing a low energy, e.g. 1-100 eN, source of electrons, to prevent the diamond from becoming charged.
• the sample is removed from the vacuum chamber, placed in a stainless steel crucible, and covered with a powerful oxidising agent, such as molten potassium nitrate, for a period of around one to two hours.
• a powerful oxidising agent such as molten potassium nitrate
• the sample is subsequently cooled and removed from the potassium nitrate before being cleaned using water and ethanol, thereby removing the portions of the diamond surface which have been disordered by the ion beam, and leaving a series of closely spaced grooves each around 30 - 35 nm deep, with no evidence of blackening.
• the exposed region Upon examination before cleaning, the exposed region is identifiable by its graphitelike appearance when examined, for example, in a reflected light microscope. Such a mark would not be acceptable to a diamond grader, in that it would substantially reduce the clarity grade of the diamond. However, after cleaning using the powerful oxidising agent, the mark is not easily visible in a microscope, with no contrast between the mark and surrounding areas. The mark only becomes visible when illuminated by preferably two directional light sources at an angle which corresponds to the angle of diffracted light of a particular wavelength, for example blue light, at which time the mark appears blue. Such a mark is acceptable to a diamond grader in that it does not detrimentally affect the clarity grade of the diamond.
• the closely spaced grooves are preferably formed within an 'invisible outline' of an alphanumeric character or the like, as shown in Figure 1 of the drawings.
• the marked diamond 104 is placed on the viewing surface 100 of a conventional microscope 102.
• the diamond 104 is illuminated by two directional light sources 106 having an angle ⁇ relative to the vertical axis Y.
• ⁇ is chosen so that the mark appears to be, for example, blue or red, as desired.
• d is approximately 1200nm, then ⁇ is chosen to satisfy:
• the directional light sources may be provided by a generally ring-shaped illuminator, all but two diametrically opposite portions thereof being masked off. However, any suitable light source may be used to produce the same effect.

Landscapes

• Adornments (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Welding Or Cutting Using Electron Beams (AREA)

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Publications (2)

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• 1997
  • 1997-12-24 GB GBGB9727364.3A patent/GB9727364D0/en not_active Ceased
• 1998
  • 1998-12-22 GB GB9828393A patent/GB2332651B/en not_active Expired - Lifetime
  • 1998-12-23 WO PCT/GB1998/003889 patent/WO1999033671A1/en active IP Right Grant
  • 1998-12-23 JP JP2000526381A patent/JP4497720B2/ja not_active Expired - Lifetime
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  • 1998-12-23 AU AU17743/99A patent/AU746557B2/en not_active Ceased
  • 1998-12-23 ZA ZA9811838A patent/ZA9811838B/xx unknown
  • 1998-12-23 RU RU2000119785/12A patent/RU2215659C2/ru active
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  • 1998-12-31 TW TW087122018A patent/TW458836B/zh not_active IP Right Cessation
• 1999
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• 2009
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