Abstract:
A method for shaping a gemstone comprising the steps of 1) attaching a gemstone to a dop, 2) holding the gemstone against a rotating lap wheel, and 3) shaping the gemstone on the lap wheel. The surface of the lap wheel is a metal abrasive material comprising a base having a plurality of pyramidal shapes protruding therefrom, a portion of the protrusions having a substantially polygonal base and triangular sides which meet at an apex which substantially forms a point, hereinafter pyramidal protrusions, and a portion of the protrusions having a substantially polygonal base and substantially trapezoidal sides with the portion thereof distant from the base surface forming a plateau such that the protrusions are substantially butte-like in shape, hereinafter termed butte protrusions, the protrusions providing intermixing cutting and planing edges, the ratio of the pyramidal protrusions to the butte protrusions ranging from 100:0 to 0:100. Also provided is the metal abrasive material used to carry out the method.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of faceting, shaping and polishing gemstones. The present invention also relates to abrasive materials for faceting and polishing precious gemstones and for shaping and polishing semi-precious gemstones. 
       BACKGROUND OF THE INVENTION 
       [0002]    Precious gemstones include diamonds, rubies, emeralds and sapphires. 
         [0003]    Diamonds have the greatest hardness of any gemstone with a hardness of 10 on the Moh&#39;s scale. Rough diamonds are generally cleaved, i.e., split along the grain, using a thin steel knife blade or sawn using a diamond saw or laser to separate the rough diamond into individual pieces. 
         [0004]    This is followed by rough shaping by bruting, i.e., grinding a cleaved diamond against a cleaved diamond to form each into a round shape or rubbing a cleaved diamond with another diamond or diamond chip to form a fancy shape such as a square or rectangle. Then, facets are polished onto the diamond using a revolving horizontal metal wheel, or lap, charged with diamond dust and oil. 
         [0005]    Lap wheels, or laps are also used for faceting other precious gemstones, including rubies, emeralds, and sapphires, as well as more transparent semi-precious gemstones, such as, for example, amethyst, topaz, garnet, aquamarine, tourmaline, and citrine. 
         [0006]    Gemstones which are opaque and generally softer than gemstones which are faceted are shaped as cabochons, usually flat on the back side and domed on the face with an elliptical or a round shape. Modifications or the elliptical or round shapes are occasionally used to avoid flaws in the stones, emphasize particular color variations in the stone, or to provide shapes such as hearts or teardrops. Cabochons are cut to shape using a band saw or trim saw. The back side is polished flat and the face is then shaped and polished using a lap wheel. The abrasive material used on the lap surface is usually particulate, either bonded to a backing or charged onto the lap wheel surface. 
         [0007]    For faceting, the gemstone is customarily held on a dop, an elongated shaft, using an appropriate glue, and fastened into a holder on a flat lap machine at a specific angle against the abrasive lap surface to produce the facet. The dop is rotated and moved as necessary to produce the desired faceting on the gemstone. In shaping cabochons, the gemstone is also held on a dop with glue or wax, but is normally hand held and rotated against the abrasive lap surface. Typically, the lap wheel is cooled and/or lubricated with oil or water depending on the gemstone being faceted or formed into a cabochon. Both faceting gemstones and forming gemstone cabochons will hereinafter be termed “shaping” gemstones, unless necessary to be specific for clarity. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention, in one aspect, provides a method for shaping a gemstone comprising the steps of
       1) attaching a gemstone to a dop,   2) holding the gemstone against a rotating lap wheel, and   3) shaping the gemstone on the lap wheel,
 
wherein the surface of the lap wheel is a metal abrasive material comprising a base having a plurality of pyramidal shapes protruding therefrom, a portion of the protrusions having a substantially polygonal base and triangular sides which meet at an apex which substantially forms a point, hereinafter pyramidal protrusions, and a portion of the protrusions having a substantially polygonal base and substantially trapezoidal sides with the portion thereof distant from the base surface forming a plateau such that the protrusions are substantially butte-like in shape, hereinafter termed butte protrusions, the protrusions providing intermixing cutting and planing edges, the ratio of the pyramidal protrusions to the butte protrusions ranging from 100:0 to 0:100.
       
 
         [0012]    The metal abrasive, having a base unitary with the protrusions, is preferably formed from metal alloys such as, for example, stainless steel, spring steel, cold rolled steel, titanium alloys, and molybdenum alloys. Particularly preferred are stainless steel and spring steel. 
         [0013]    The abrasive protrusions, unitary with the base, may be arranged in rows, spiral, helix, or lattice fashion, or may be randomly spaced. The arrangement, height, and shape or the abrasive protrusions helps to define the rate of surface removal in shaping the gemstone. 
         [0014]    The protrusions of the abrasive material useful in the invention may be the same or different in shape. For example, various protrusions may have different bases configurations, i.e., different numbers of sides, and/or different degrees of slope with some bases approaching a circular shape. Generally, a triangular base is preferred. The triangular sides of the pyramidal protrusions and the trapezoidal sides of the butte protrusions may have an inward arcuate slope. 
         [0015]    The abrasive material useful in the invention may be subjected to high and/or low temperature treatment. Heat treatment, i.e., annealing is particularly useful to remove stress in cold rolled steel. Optional performance enhancing surface treatments may be applied to the protrusions and the base surface to improve abrasive performance, increase abrasive endurance, aid in non-loading characteristics due to the lubricity of certain coatings, and reduce surface porosity. 
         [0016]    The abrasive material for use on a lap machine is provided as a disk usually 6 inches or 8 inches in diameter although disks as large as 12 inches in diameter or larger may be used. The abrasive material can be adhered to the lap wheel by means well known to those skilled in the art. The abrasive material may also be in the form of a small disk preferably having a diameter of from about 0.5 inch to about 1.5 inches, more preferably from about 0.75 inch to 1 inch or in the form of a small drum preferably having a diameter of from about 0.5 inch to about 1.5 inches, more preferably from about 0.75 inch to 1 inch for use with a hand held high-speed rotary tool. A hand held high-speed rotary tool is suitable for use in the method of the invention for producing cabochons with shapes such as, for example, hearts or crosses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIGS. 1A ,  1 B, and  1 C are perspective views of pyramidal protrusions suitable for the abrasive material useful in the method of the present invention. 
           [0018]      FIG. 2A  is a cross-sectional view of an abrasive material having pyramidal protrusions on both surfaces thereof useful in the present invention. 
           [0019]      FIG. 2B  is a cross-sectional view of an abrasive material invention having pyramidal protrusions of varying heights on the surface thereof useful in the present. 
           [0020]      FIG. 3  is cross-sectional view of a pyramidal protrusion having a performance enhancing coating thereon useful in the present invention. 
           [0021]      FIG. 4A  is a perspective view of a pyramidal protrusion having triangular sides with a slope of about 30° which meet at an apex which substantially forms a point useful in the present invention. 
           [0022]      FIG. 4B  is a perspective view of a pyramidal protrusion having triangular sides with a slope of about 20° which meet at an apex which substantially forms a point useful in the present invention. 
           [0023]      FIG. 4C  is a perspective view of a preferred pyramidal protrusion useful in the present invention having triangular sides with a slope of about 40° which meet at an apex which substantially forms a point. 
           [0024]      FIG. 5A  is a cross-sectional view of a butte protrusion having a slope of about 45° and a plateau distant from the base surface an amount equivalent to 90% of a pyramidal protrusion having a 45° slope. 
           [0025]      FIG. 5B  is a cross-sectional view of a butte protrusion having a slope of about 45° and a plateau distant from the base surface an amount equivalent to 80% of a pyramidal protrusion having a 45° slope. 
           [0026]      FIG. 5C  is a cross-sectional view of a butte protrusion having inward arcuate sides and a plateau distant from the base surface an amount equivalent to 70% of a pyramidal protrusion with a 45° slope. 
           [0027]      FIG. 6A  is a fragmented top view of a portion of a mask suitable for use in producing an abrasive material suitable for use in the present invention. 
           [0028]      FIG. 6B  is a fragmented top view of the mask shown in  FIG. 6A  enlarged 400×. 
           [0029]      FIG. 6C  is a fragmented top view of an abrasive material enlarged 400× having pyramidal protrusions which can be produced using the mask shown in  FIGS. 6A and 6B . 
           [0030]      FIG. 6D  is a fragmented top view of an abrasive material enlarged 400× having butte protrusions with plateaus distant from the base surface an amount equivalent to 80% of the height of a pyramidal protrusion having a similar slope which butte protrusions can be produced using the mask shown in FIGS. A and  6 B. 
           [0031]      FIG. 7A  is a fragmented top view of a portion of an abrasive material useful in the present invention. 
           [0032]      FIG. 7B  is a fragmented top view of a mask enlarged about 400× useful for producing the abrasive shown in  FIG. 7A . 
           [0033]      FIG. 8  is a fragmented top view of an abrasive disk useful in the present invention with a portion shown at 400×. 
           [0034]      FIG. 9  is a fragmented top view of an abrasive disk useful in the present invention with a portion shown at 400×. 
           [0035]      FIG. 10A  is a top view of a disk useful in the present invention. 
           [0036]      FIG. 10B  shows the disk of  FIG. 10A  enlarged about 400×. 
           [0037]      FIG. 11A  is a top view of a disk useful in the present invention. 
           [0038]      FIG. 11B  shows the disk of  FIG. 11A  enlarged about 400×. 
           [0039]      FIG. 12A  is a side view of an abrasive material for use as a drum abrasive in the present invention. 
           [0040]      FIG. 12B  is a perspective view showing the manner in which the abrasive material of  FIG. 12A  is used to form a cylindrical drum. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    In the method for shaping gemstones of the present invention, the abrasive material is formed from metal alloys such as, for example, stainless steel, spring steel, cold rolled steel, titanium alloys, and molybdenum alloys. Particularly preferred are stainless steel and spring steel. 
         [0042]    Stainless steel and spring steel are a particularly preferred base materials in the present invention due to the intrinsic resistance of the material to corrosion and the ability of the metal to be readily reproducibly etched to form the abrasive material useful in the invention. 
         [0043]    The method of the present invention is distinctly advantageous in that the abrasive used is formed by etching a pattern of protrusions from the material which forms the base, i.e. the abrasive substrate. When faceting the harder gemstones using prior methods, abrasive particulate is charged on a wheel with oil and, as the faceting process progresses, additional abrasive particulate and oil are added to maintain the abrasiveness of the wheel. When shaping softer gemstones using prior abrasive materials, e.g., sandpaper and sanding disks which have particulate such as, for example, garnet, aluminum oxide, silicon oxide, and other hard abrasive particles, adhered to a backing by a binder system, the particulate is dislodged from the surface of the abrasive. Such loss of abrasive particulate results in deterioration of the abrasive material. 
         [0044]    The etching process can be carried out using resist and etching materials and processes which are well known to those skilled in the art. Prior to application of the photoresist to the base material, cleaning of the base material is preferably carried out. The resist coating can be applied using, for example, hot roll lamination, screen printing, gravure printing, dip coating and the like. 
         [0045]    The mask which is used to provide the desired abrasive pattern surface is then placed on the resist covered base material. Good, i.e., intimate, contact between the resist coating and the mask is needed to achieve the desired pattern on the base material where the photoresist not covered by the mask is cured. Curing, or imaging, is achieved by exposure to light sufficient to cure, i.e., cross-link, the polymeric resist. The mask is then removed from the base material/photoresist/mask composite and the uncured photoresist is removed from the base material using a developing solution, or developer. If desired, the photoresist then remaining on the base material may be imaged again prior to etching to further ensure good adhesion of the photoresist to the base material during etching. 
         [0046]    Etching is then performed on those portions of the base material not protected by the photoresist. The degree of etching can be adjusted by altering the concentration and temperature of the etchant solution and the method of application as is known to those skilled in the art. As etchant removes the base material, a certain portion of the base material under the mask also is exposed. 
         [0047]    The rate of etching and the extent to which this is allowed to continue determines the shape of the protrusions. To achieve the pyramidal protrusions requires etching to a greater extent than etching to achieve the butte protrusions. To achieve mixed pyramidal protrusions and butte protrusions, having mask portions of differing surface areas can be used with larger mask areas producing butte protrusions and smaller mask areas producing pyramidal protrusion. 
         [0048]    The rate of etching also determines the extent to which an inward arctuate slope is formed. Generally, a faster rate of etching results in a greater inward arc. 
         [0049]    On thinner base materials where only one side of a substrate carries the abrasive pattern, both side of the base material may be etched to equalize metal stresses and reduce curling. 
         [0050]    After etching, any remaining photoresist may be removed by techniques well known to those skilled in the art. 
         [0051]    The thickness of the abrasive material is not particularly limited, but after etching should be suitably stiff when used as a flat abrasive. Of course, stiffness can be provided, if necessary, by attachment to a stiff substrate such as, for example, a metal plate or synthetic resin plate having suitable stiffness. 
         [0052]    In the method of the present invention the surface of the abrasive material can be heat treated, cryogenically treated or heat treated and cryogenically treated or metallurically altered, e.g., case hardening, for example, to form a thin harder layer on the surface of the base surface and protrusions to improve hardness as is well known to those skilled in the art. 
         [0053]    Performance enhancing coatings may optionally be applied to the surface of the abrasive useful in the present invention. Preferred coatings include, for example, titanium nitride, chromium nitride, boron nitride and diamond or diamond-like coatings. Such coatings may be applied, for example, by chemical vapor deposition, plasma-assisted chemical vapor deposition, hypersonic plasma particle deposition, or physical vapor deposition, as appropriate for material being deposited as is well known in the art. Performance enhancing coatings such as, for example, nickel or chrome plating or plating in combination with diamond dust may also be applied to the abrasive material for use in the invention. Performance enhancing coatings are particularly preferred when the abrasive material is used for faceting precious gemstones and other gemstones having higher Moh&#39;s hardness. 
         [0054]    With respect to the drawings, like references number will be used with reference to like parts. 
         [0055]      FIGS. 1A ,  1 B, and  1 C depict various possible embodiments of the pyramidal protrusions of the abrading material of the invention with the bases of the pyramidal protrusions being triangular, square and pentagonal, respectively. Of course, other polygonal shapes can be used. In  FIG. 1A , protrusion  10   a  is shown having triangular base  12   a,  triangular side  14   a,  and apex  16   a.  In  FIG. 1B , protrusion  10   b  is shown having square base  12   b,  triangular side  14   b  and apex  16   b.  In  FIG. 1C , protrusion  10   c  is shown having polygonal base  12   c,  triangular side  14   c  and apex  16   c.  The protrusion can also have a base approaching a circle. 
         [0056]      FIG. 2A  depicts abrasive material  20   a  useful in the invention having pyramidal protrusions on both sides of base  22   a  with sides  24   a  and apexes  26   a  extending from base  22   a.  In  FIG. 2B , abrasive material  20   b  with pyramidal protrusion  22   b  having side  26   b  and having a certain elevation from base  24   b  and pyramidal protrusion  23   b  having side  27   b  and having a lesser elevation from base  24   b.  Of course, butte protrusions or mixed pyramidal protrusions and butte protrusions may be formed of varying heights on a substrate surface. 
         [0057]      FIG. 3  shows abrasive material  30  having pyramidal protrusion  32  with height H and base width W on base  34  having a thickness B. On the surface of protusion  32  and exposed base  34  is performance enhancing coating  38 . 
         [0058]    Preferably, the slope of the sides of the pyramidal protrusions or the butte protrusions can vary from slight, e.g., about 20° or less to about 45° , more preferably from about 25° to about 40° , most preferably from about 30° to 35° . In  FIGS. 4A ,  4 B, and  4 C, the slopes of the sides of the pyramidal protrusions are 30°, 20° and 40°, respectively. The slope of the sides of the protrusions can be controlled by the adhesion of the cured photoresist and the rapidity of the formation of the protrusions. For example, when etching a stainless steel sheet with a ferric chloride solution, a protrusion having a lesser slope can be formed by using a photoresist which may have lower adhesion and/or adjusting the ferric chloride to etch more slowly. 
         [0059]      FIGS. 5A ,  5 B, and  5 C depict various types of butte protrusions of the abrasive material useful in the method of the present invention having varying amounts of height compared to comparable pyramidal protrusions. In  FIG. 5A , protrusion  50   a  is shown having side  52   a,  base  54   a,  a flat top portion  56   a  and height about 90% of that of a pyramid with comparable slope. In  FIG. 5B , protrusion  50   b  is shown having side  52   b,  base  54   b,  a flat top portion  56   b  and height about 80% of that of a pyramid with comparable slope. In  FIG. 5C , protrusion  50   c  is shown having side  52   c,  base  54   c,  a flat top portion  56   c  and height about 70% of that of a pyramid with slope extending from the base to the outer edge of flat top portion  56   c.  However, in  FIG. 5C , etchant has removed substrate material from under the photoresist which covered portion  56 C, to leave undercut  58   c.  On a pyramidal protrusion where etchant removes some material under the photoresist, an inward arctuate slope of the side would result. 
         [0060]      FIG. 6A  shows a portion of an abrasive material for use in the present invention. In  FIG. 6B , enlarged mask portion  60   b,  which mask pattern can be used to produce the abrasive material of  FIG. 6A , has clear portions  61   b′  which allow the light to pass through to cure the photoresist. Surrounding the clear portions are the opaque portions  63   b′  which prevent curing of the photoresist. 
         [0061]    After curing of the photoresist and removal of the mask, the uncured photoresist is removed by rinsing with a solution appropriate for the photoresist used. The substrate etches, when subjected to an etchant bath, such that pyramidal protrusions or butte protrusions are formed under the areas of the cured photoresist with the base surface being formed in the areas having no photoresist. In some cases where pyramidal protrusions are being formed, the photoresist may be removed during the etching process. 
         [0062]    In  FIG. 6C , an abrasive material useful in the present invention is shown enlarged 400×. Abrasive material  60   c,  which can be produced using a mask as shown in  FIG. 6B , has pyramidal protrusions  61   c  extending from base  63   c.  In  FIG. 6D , another abrasive material useful in the present invention is shown enlarged 400×. Abrasive material  60   d,  which can be produced using a mask as shown in  FIG. 6B , has butte protrusions  65   d  extending from base  63   d.  Protrusions  65   d  are similar in shape to protrusion  50   b  shown in  FIG. 5B . 
         [0063]    In  FIG. 7A , a portion of an abrasive material useful in the present invention is shown. A mask portion shown enlarged 400× in  FIG. 7B  is suitable for use in making the abrasive material shown in  FIG. 7A . In  FIG. 7B , enlarged mask  70   b  has clear portions  71   b′  which allow the light to pass through to cure the photoresist. Surrounding the clear portions are the opaque portions  73   b′  which prevent curing of the photoresist. After etching, protrusions are formed in the areas of cured photoresist, with base material remaining in the etched areas having no protoresist. 
         [0064]      FIG. 8  is a top view of a portion of an abrasive disk  80  useful in the present invention. Disk  80  has a diameter of about 6 inches and may be attached to a lap machine at arbor  85 . A portion of the disk enlarged about 400× shows the footprint of protrusions  81  on base  83 . 
         [0065]      FIG. 9  is a top view of a portion of an abrasive disk useful in the present invention having a pattern different from that shown in  FIG. 8 . The disk has a diameter of about 10 inches and the detail can be seen more clearly in the portion shown at 400×. 
         [0066]      FIGS. 10A and 11A  show small disks for use on a hand held high-speed rotary tool.  FIGS. 10B and 11B  show disks  10 A and  11 A, respectively, at about 400× such that the abrasive pattern is more visible. 
         [0067]      FIG. 12A  shows an abrasive material for use on a drum attachment of a hand held high-speed rotary tool.  FIG. 12B  depicts the manner in which the abrasive material shown in  FIG. 12A  is welded at weld line  129   b  to suitably be used on the drum attachment. 
       EXAMPLES 
     Example 1 
       [0068]    A sheet of 420 spring tempered stainless steel having a thickness of about 0.032 inch was cleaned and passivated. A photoresist solution was coated onto the passivated stainless steel and dried. A mask having pattern as shown in  FIG. 6B  was applied over the photoresist. 
         [0069]    The stainless steel/photoresist/mask composite was exposed to 60 millijoules of light to effect imaging of the photoresist. The unexposed, uncrosslinked photoresist was then removed by rinsing with a developer solution. The stainless steel having the photoresist pattern thereon was re-exposed to 100 millijoules light to ensure adherence of the photo resist to the stainless steel during etching. 
         [0070]    The stainless steel was etched to a depth of about 0.012 inch using 36 Baume ferric chloride solution at a temperature of 145° F. The resulting etched sheet was rinsed with water and the remaining photoresist was removed using an aqueous potassium hydroxide stripping solution. 
         [0071]    The etched stainless steel was coated with titanium chromium nitride at a temperature of about 500° F. and subsequently cryogenically cooled at −300° F. 
         [0072]    The resulting abrasive material had pyramidal protrusions with triangular bases. The height of the apexes of the protrusions from the base material was about 0.002 inch and a slope of about 30°. The resulting abrasive material was a coarse gemstone abrasive. The material was satisfactory for cutting into disks for use on a lap wheel. 
       Example 2  
       [0073]    A sheet of 420 spring tempered stainless steel having a thickness of about 0.020 inch was cleaned and passivated. A photoresist solution was coated onto the passivated stainless steel and dried. A mask having pattern like that of  FIG. 7B  was applied over the photoresist. 
         [0074]    The stainless steel/photoresist/mask composite was exposed to 60 millijoules of light to effect imaging of the photoresist. The unexposed, uncrosslinked photoresist was then removed by rinsing with a developer solution. The stainless steel having the photoresist pattern thereon was re-exposed to 100 millijoules light to ensure adherence of the photo resist to the stainless steel during etching. 
         [0075]    The stainless steel was etched to a depth of about 0.003 inch using 36 
         [0076]    Baume ferric chloride solution at a temperature of 145° F. The resulting etched sheet was rinsed with water and the remaining photoresist was removed using an aqueous potassium hydroxide stripping solution. 
         [0077]    The etched stainless steel was coated with titanium chromium nitride at a temperature of about 500° F. and subsequently cryogenically cooled at −300° F. 
         [0078]    The resulting abrasive material had pyramidal protrusions with triangular bases. The height of the apexes of the protrusions from the base material was about 0.002 inch and the slope of the sides of the protrusions was about 30°. The resulting abrasive material was a fine gemstone abrasive. The material was satisfactory for cutting into disks for use on a lap wheel. 
         [0079]    Although the present invention has been described with reference to preferred embodiments, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.