Abstract:
A composition for forming metal objects includes (a) first particles containing a jewelry-metal, and (b) second particles containing a refractory metal oxide. The composition allows the preparation of jewelry-metal in a large variety of colors.

Description:
BACKGROUND  
         [0001]    The present invention relates to metal clays with refractory stains.  
           [0002]    Upon sintering, jewelry-metal clays form pure or almost pure jewelry-metal objects that retain the basic shape of the jewelry-metal clay. The clays contain a jewelry-metal powder and a binder; the binder is mostly removed during the sintering process. Jewelry-metal clays are described in U.S. Pat. Nos. 5,376,328 and 5,328,775. Jewelry-metal clay is referred to in the trade as precious metal clay, or PMC, and is available from RIO GRANDE, 7500 Bluewater Road N.W., Albuquerque, N. Mex., 87121, among others.  
           [0003]    The ability to color jewelry-metal objects is limited. Jewelry-metal gold is an excellent example. Although white, rose, green, and varying shades of yellow gold are known, each is made by alloying pure gold with a second metal. The achievable color variation in any jewelry-metal, whether 24 karat gold, 18 karat gold, 14 karat gold, 10 karat gold, Nu-gold (88% wt. Cu/12% wt. Zn), fine silver, sterling silver (92.5% wt. Ag/7.5% wt. Cu), nickel silver (65% wt. Cu/18% wt. Ni/17% wt. Zn), platinum, palladium, ruthenium, rhodium, aluminum, brass, lead, nickel, iridium, indium, copper, zinc, or combinations thereof, is typically limited to the alloys these metals form. Accordingly, there is a need to expand the varieties of colors of jewelry-metal articles.  
           [0004]    Refractory stains have many uses and are widely used to color ceramics. Prior to firing, the stain is incorporated into the slip and/or applied as a glaze. The stains are prepared by mixing together metal oxides and various inorganic and metal binders, which are fired for color stability, and then ground.  
         BRIEF SUMMARY  
         [0005]    In a first aspect, the present invention includes a composition for forming metal objects, including first particles containing a jewelry-metal, and second particles including a refractory metal oxide. The composition may be made by mixing these ingredients together.  
           [0006]    In a second aspect, the present invention includes a metal object, containing a jewelry-metal; and second particles containing a refractory metal oxide, in the jewelry-metal.  
         DETAILED DESCRIPTION  
         [0007]    Jewelry-metal clays and refractory stains may be combined to form a colored metal clay. When sintered, the colored metal clay forms a colored jewelry-metal article, due to incorporation of the stain. Because jewelry-metal clays are sintered to remove their binder constituents at temperatures lower than those at which refractory stains degrade, jewelry-metals having the color of the stain are possible. The stain is present on the surface and in the subsurface of the finished jewelry-metal article, not simply as a surface coating. The actual color of the final product will be influenced by the natural color of the jewelry-metal and the color of the stain.  
           [0008]    Jewelry-metal clays form almost pure jewelry-metal articles after sintering, preferably at temperatures of from 1470° F. to 1830° F. Because refractory stains do not undergo significant chemical reaction and degradation during sintering at these, and higher, temperatures, the stains may be incorporated into the jewelry-metal clays. In the case of jewelry-metals which cannot tolerate sintering in air without significant oxidation, sintering may be carried out under vacuum, under an inert atmosphere, such as argon or nitrogen, or under a reducing atmosphere, such as hydrogen or methane.  
           [0009]    Although the coloring of jewelry-metal objects is preferably achieved by mixing a refractory stain into a jewelry-metal clay before sintering, clays are not required. A jewelry-metal may be colored with stain, for example, by mixing the powdered metal and stain together, and then sintering the mixture below the melting point of the metal. Furthermore, once formed by any method, colored jewelry-metal may be mechanically formed into the desired shape using hand-tools, machines, or dies. Colored jewelry-metal wires could be produced in this manner.  
           [0010]    As described in U.S. Pat. Nos. 5,328,775 and 5,376,328, a pure or almost pure jewelry-metal object may be formed as the solid-phase sintered product of a jewelry-metal clay. To manufacture the jewelry-metal article, a moldable clay mixture, containing a jewelry-metal powder and a binder, is shaped into a molded object. The molded object is then sintered An almost pure jewelry-metal article results which retains the shape of the clay, typically with some shrinkage. To prevent the metal from melting and loosing the shape into which the clay was molded, the clay is sintered at a lower temperature than the melting point of the jewelry-metal. Sintering is defined as heating sufficiently to cause the metal particles to stick together, but below the melting point of the metal.  
           [0011]    Moldable clay mixtures are produced by blending jewelry-metal powders with a binder. Preferably, the binder is a cellulose binder prepared by blending a cellulose with water. Addition of a surface-active agent during mixing of the jewelry-metal powder and binder allows for more uniform mixing in a short time period. Addition of an adhesion-preventing agent, such as di-n-butyl phthalate or an oil such as a vegetable oil, prevents the clay from sticking to the skin of the hand during molding.  
           [0012]    A preferable moldable clay mixture contains 50 to 90% by weight of jewelry-metal powder with an average particle diameter of at most 1000 μm, preferably at most 600 μm, most preferably at most 200 μm; 0.8 to 8% by weight of binder, more preferably a water-soluble cellulose binder; 0.08 to 3% by weight of a surface-active agent; and 0.1 to 4% by weight of oil; with the balance water and unavoidable impurities. Sintering of this jewelry-metal clay results in a solid-phase sintered product of a jewelry-metal.  
           [0013]    Currently, three jewelry-metal clays are available from RIO GRANDE. An 80% pure silver clay (STANDARD SILVER PMC) is available with a recommended sintering time of two hours at 1650° F. A 90% pure silver clay (SILVER PMC+) is available with a recommended sintering time of thirty minutes at 1470° F. This clay provides the benefits of less shrinkage, lower sintering temp, and less sintering time. A 24 karat yellow gold clay (STANDARD GOLD PMC) is also available with a recommended sintering time of two hours at 1830° F. Other jewelry-metal clays may be prepared by mixing powder of one or more metals or alloys with a binder, optionally a solvent which will evaporate or burn away (water, ethanol, isopropanol, methanol, acetone, etc.), optionally a surface-active agent, and optionally an adhesion-preventing agent (di-n-butyl phthalate, vegetable oil, etc.).  
           [0014]    Jewelry-metal clays may also be formed by more conventional methods involving the combination of jewelry-metal powders and binders such as bentonite, clay, glue, and boiled rice or wheat flower, and optionally water, as described in Japanese Patent Applications laid open with Publication Numbers 59-143001 and 63-403. Unlike cellulose-binder clays, these binders may remain in the jewelry-metal article after drying or sintering.  
           [0015]    Refractory stains have been used to color ceramic articles for over 100 years and are available in numerous colors. In addition to shades of pink, blue, black, white, crimson, coral, purple, orange, gray, green, brown, yellow, and red, many color shades are available. Refractory stains may be obtained as MASON STAINS, available from MASON COLOR WORKS, INC., East Second Street, P.O. Box 76, East Liverpool, Ohio, 43920, or as WALKER STAINS, available from WALKER CERAMICS, 55 Lusher Road, Croydon, Australia, 3136.  
           [0016]    Refractory stains are metal oxides which are fired for color stability to form refractory metal oxides and ground into a fine powder with an average particle diameter of at most 50 mesh (for example 254 to 297 microns), preferably at most 100 mesh (for example 122 to 149 microns), and most preferably at most 200 mesh (for example 50 to 74 microns). One or more oxides of metals such as aluminum (Al 2 O 3 ), antimony (Sb 2 O 3 ), boron (B 2 O 3 ), calcium (CaO), chromium (Cr 2 O 3 ), cobalt (CoO), iron (Fe 2 O 3 ), manganese (MnO 2 ), nickel (NiO), praseodymium (Pr 6 O 11 ), selenium (SeO 2 ), silicon (SiO 2 ), tin (SnO 2 ), titanium (TiO 2 ), vanadium (V 2 O 5 ), zinc (ZnO), and zirconium (ZrO 2 ) are combined in various proportions and then fired, to attain the desired color. In addition to metal oxides, refractory stains optionally contain various metal and inorganic binders. Any combination may be used, as long as the metal oxide stain can withstand firing at a temperature high enough to allow sintering of the metal clay.  
           [0017]    The stains may be any color, including black, white, or transparent. To achieve greater color variation, mixtures of stains are possible. Some examples of the available stain colors and the metal oxide components combined to form them are provided in the following MASON COLOR charts.  
                                                                                                                                                                                                                                                                                                                                                                                                                     MASON COLOR COMPOSITION CHARTS                                New                                                           See       No.   Greens   Al   Ca   Co   Cr   Fe   Ni   Pr   Si   Sn   Ti   V   Zn   Zr   Ref.               6200   Evergreen           X   X               X                       3, 5       6201   Celadon   X       X   X               X               X       1, 3,                                                                   6, 8       6202   Florentine           X   X               X                       1, 3,                                                                   6, 8       6204   Victoria Green       X       X               X                   X   3, 5,                                                                   9       6206   Grass Green       X       X               X                   X   3, 5,                                                                   9       6207   Celeste           X   X               X               X       1, 3,                                                                   6       6209   Chrome Green               X               X                       3, 5       6211   Pea Green                               X       X   X       X   1, 3,                                                                   6, 8       6219   French       X   X   X               X               X       1, 3,                                                                   5, 8       6221   Turquoise       X   X   X               X               X   X   3, 5       6223   Ivy   X           X               X                       3, 5       6224   Dk. Green           X   X   X           X               X       3, 5       6226   Dk. Leaf           X   X   X           X               X       1, 3,                                                                   6, 8       6234   Myrtle Green   X       X   X                                       1, 3,                                                                   6, 8       6236   Chartreuse                               X       X   X       X   1, 3,                                                                   6       6242   Bermuda                           X   X           X       X   3, 6       6244   Deep Sea   X       X   X               X               X       1, 3,                                                                   6, 8       6246   Blue Green           X   X               X   X           X       3, 6,                                                                   8       6254   Dk. Teal Green   X       X   X               X               X       1, 3,                                                                   6, 8       6255   Jade Green   X       X   X               X               X       1, 3,                                                                   6, 8       6263   Victoria       X       X               X                   X   3, 5,                                                                   9       6264   Victoria       X       X               X                   X   3, 5,                                                                   9       6265   Leaf Green       X   X   X               X               X   X   3, 5,                                                                   9       6266   Peacock           X   X                                       1, 3,                                                                   6, 8       6267   Emerald       X   X   X               X                   X   3, 5,                                                                   9       6268   Sea Green           X   X               X               X       1, 3,                                                                   6, 8       6271   Mint       X   X   X               X               X   X   3, 5,                                                                   9       6274   Nickel Silicate                       X       X                       1, 3       6280   Avocado   X       X   X   X           X       X   X   X   X   3, 6       6288   Turquoise       X       X               X           X       X   3, 5,                                                                   9       6296   Dk. Spruce       X   X   X               X                       1, 3,                                                                   6, 8                    New                                   See       No.   Blacks   Co   Cr   Fe   Mn   Ni   Sn   Zn   Ref.               6600   Best Black   X   X   X       X           1, 3, 6       6601   Velvet Black   X   X   X       X       X   1, 3, 6       6609   Black   X   X   X   X   X   X       1, 3, 6       6612   Onyx Black   X   X   X       X           1, 3, 6       6616   Chrome-Free   X       X   X               1, 3, 6       6650   Cobalt-Free       X   X                   3, 5       6657   Black   X   X   X                   3, 5       6666   Cobalt-Free       X   X   X               3, 5                    New                                               See       No.   Blues   Al   Co   Cr   Fe   Ni   Si   Sn   V   Zn   Zr   Ref.               6300   Mazerine       X               X           X       1, 3, 6       6302   Cadet   X   X   X           X   X       X       1, 3, 6       6305   Teal   X   X   X           X           X       1, 3, 6       6306   Vivid Blue   X   X               X           X       1, 3, 6       6307   Pastel Blue   X   X                   X           X   1, 3, 6       6308   Delphinium   X   X                   X               1, 3, 6       6310   Wedgwood   X   X               X                   1, 3, 6       6313   Medium Blue       X               X           X       1, 3, 6       6315   Zirconium                       X       X       X   1, 3, 6           Vanadium       6320   Delft   X   X               X   X       X       1, 3, 6       6330   Cobalt Aluminate   X   X                                   1, 3, 6       6336   Peacock   X   X   X           X   X       X       3, 6       6338   Cobalt Meta-       X               X                   1, 3, 6           Silicate       6339   Royal   X   X                           X       1, 3, 6       6343   Mediterranean   X   X   X           X           X       1, 3, 6       6350   Bright Blue   X   X               X       X   X   X   1, 3, 6       6360   Willow   X   X   X           X   X               3, 5       6363   Sky Blue   X   X               X                   1, 3, 6       6364   Turquoise                       X       X       X   1, 3, 6       6368   Copen Blue   X   X               X           X       1, 3, 6       6371   Dark Teal   X   X   X                               1, 3, 6       6373   Turquoise       X   X               X   X       X   3, 6       6374   Dk. Turquoise                       X       X       X   1, 3, 6       6376   Robin&#39;s Egg                       X       X       X   1, 3, 6       6378   Zirconium                       X       X       X   1, 3, 6           Vanadium       6383   Cobalt Aluminate   X   X                                   1, 3, 6       6386   Navy Blue       X   X   X   X   X           X       1, 3, 6       6388   Mazerine       X               X                   1, 3, 6       6389   Sapphire Blue   X   X                                   1, 3, 6       6391   Zirconium                       X       X       X   1, 3, 6           Vanadium       6393   Turquoise   X   X               X   X   X       X   3, 6       6396   Peacock   X   X   X           X       X       X   1, 3, 6       6398   Deep Peacock   X   X   X                               1, 3, 6                    New                               See       No.   Whites   Al   B   Ca   Si   Sn   Zr   Ref.               6700   White   X           X       X   3, 6       6768   Tin White   X           X   X       3, 6       6790   White for Matting               X       X   3, 6                    New   Pinks, Crimsons,                                           See       No.   &amp; Corals   Al   Ca   Cr   Fe   Mn   Si   Sn   V   Zn   Zr   Ref.               6000   Shell Pink           X               X               3, 5, 9       6001   Alpine Rose           X               X               3, 5, 9       6002   Rose Pink           X               X               3, 5, 9       6003   Crimson           X               X               3, 5, 9       6004   Crimson           X               X               3, 5, 9       6005   Deep Crimson           X               X               3, 5, 9       6006   Deep Crimson           X               X               3, 5, 9       6007   Peach           X               X   X           3, 5, 9       6008   Peach           X               X   X           3, 5, 9       6009   Coral           X               X   X           3, 5, 9       6020   Manganese   X               X                       1, 3           Alumina       6023   Clover Pink           X               X   X       X   3, 5       6029   Persimmon   X       X   X                   X       3, 8       6031   Deep Salmon           X   X           X               3, 5       6032   Coral               X       X               X   3       6052   Doll Flesh   X       X   X   X               X       1, 3, 6       6065   Chrome Alumina   X       X                               1, 3, 6       6067   Pink Extender       X               X   X               3, 5       6069   Dark Coral               X       X               X   3       6090   Coral           X               X   X           3, 5, 9       6098   Flesh           X               X   X       X   3, 5, 9                    New                                                   See       No.   Yellows   Al   Cr   Fe   Pr   Sb   Si   Sn   Ti   V   Zn   Zr   Ref.               6404   Vanadium   X                       X       X           1, 3, 6       6405   Naples           X   X       X                   X   3, 6       6406   Buttercup           X   X       X                   X   3, 6       6407   Marigold           X   X       X                   X   3, 6       6408   Praseodymium               X       X                   X   3, 6       6433   Praseodymium               X       X                   X   3, 6       6440   Vanadium                           X       X           1, 3, 6       6450   Praseodymium               X       X                   X   3, 6       6464   Zirconium                               X   X       X   1, 3, 6       6471   Old Gold   X   X   X               X       X   X       1, 3, 6       6485   Titanium       X           X           X               1a, 3                    New   Purples &amp;                                                   See       No.   Lavenders   Al   Ca   Co   Cr   Fe   Mn   Ni   Si   Sn   V   Zn   Zr   Ref.               6303   Deep Orchid   X       X   X                   X               3, 5, 9       6317   Lavender   X       X   X                   X       X       3, 5, 9       6318   Amaethyst   X       X   X                   X       X       3, 5, 9       6319   Lavender   X       X           X       X           X       1, 3       6324   Violet   X       X   X               X   X       X   X   3, 5, 9       6331   Orchid   X       X   X                   X       X       3, 5, 9       6332   Orchid   X       X   X                   X       X       3, 5, 9       6333   Lavender   X       X   X                   X       X       3, 5, 9       6381   Blackberry Wine           X   X   X       X   X   X               3, 5, 9       6385   Pansy Purple           X   X               X   X               3, 5, 9       6387   Mulberry   X       X   X                   X               3, 5, 9       6392   Dusty Lavender               X               X   X   X       X   3, 5, 9               New   Browns &amp;                                                   See       No.   Oranges   Al   Ca   Co   Cr   Fe   Mn   Si   Sn   Ti   V   Zn   Zr   Ref.               6100   Woodland   X           X   X       X               X       3, 6, 7       6101   Chestnut               X   X   X                   X       3, 6, 7       6103   Golden   X           X   X                       X       3, 6, 7       6104   Fawn               X               X       X       X   3, 6, 7       6107   Dk. Golden   X           X   X                       X       3, 6, 7       6108   Walnut               X   X   X                   X       3, 6, 7       6109   Deep Brown   X           X   X                       X       3, 6, 7       6110   Violet Of Iron   X               X       X                       3, 6, 7       6111   Spice Brown                   X           X           X       3, 6, 7       6113   Claret               X   X                       X       3, 6, 7       6119   Russet       X       X   X                       X   X   3, 6, 7       6121   Saturn   X           X   X                       X       3, 6, 7           Orange       6122   Cedar   X           X   X                       X       3, 6, 7       6123   Saddle   X           X   X                       X       3, 6, 7       6124   Chocolate   X           X   X   X                   X       3, 6, 7       6125   Leather   X           X   X                       X       3, 6, 7       6126   Hazelnut   X           X   X                       X       3, 7       6129   Golden   X           X   X                       X       3, 6, 7           Ambrosia       6131   Titanium Iron                   X               X               1a, 3,                                                               6       3132   Red Brown               X   X                       X       3, 6, 7       3133   Sorrel Brown               X   X                       X       3, 6, 7       6134   Red Brown               X   X                       X       3, 6, 7       6149   Iron Silicate                   X       X                       3, 6, 7       6155   Black Brown               X   X                               3, 6, 7       6153   Seal Brown               X   X   X                   X       3, 6, 7       6160   Dk. Chocolate   X           X   X   X                   X       3, 6, 7       6163   Terra Cotta   X           X   X                       X       3, 6, 7       6166   Camel Beige   X       X   X   X   X                   X       3, 6, 7       6190   Deep Brown               X   X   X                           3, 6, 7       6194   Manganese                       X   X                       3, 6, 7           Silicate               New                                                       See       No.   Greys   Al   Co   Cr   Fe   Mn   Ni   Sb   Si   Sn   Ti   V   Zr   Ref.               6500   Sage       X   X           X       X                   1, 3, 6       6503   Taupe   X       X   X               X               X   3, 5, 9       6506   Pearl       X   X   X       X           X               3, 6       6515   Soft   X       X   X   X           X               X   3, 5           Medium       6523   Soft   X   X   X   X   X   X       X   X           X   3, 5           Green       6527   Shadow   X       X   X               X   X           X   3, 5, 9       6528   Charcoal       X   X   X       X           X               3, 6       6530   Silver       X   X   X       X           X               3, 6       6531   Slate       X   X   X       X           X               1, 3, 6       6537   Mouse   X       X   X               X   X           X   3, 5, 9       6540   Blue-Grey       X   X   X       X           X               3, 6       6572   Neutral           X   X                               X   3, 5       6573   Rose           X   X                   X   X   X   X   3, 5, 9           Taupe       6584   Tin Grey                           X       X               2, 8       6591   Gun Metal       X               X                       X   3, 6                  
 
           [0018]    Reference Notes for Color Composition Charts  
           [0019]    1. Can be used as a ‘body stain’ in porcelain at high temperatures. All of the brown colors can be used as ‘body stains’ but will vary in shade considerably depending on the composition of the body and temperature at which it is fired.  
           [0020]    1a. Use only as ‘body stain’ 
           [0021]    Firing Temperatures can only be a rough guide. Firing at 2200° F. on a slow schedule may give the equivalent maturing as firing at 2300° F. on a fast schedule. The cycle, atmosphere, and rate of cooling will affect the color.  
           [0022]    2. Max. firing limit 2156° F. (1180° C.).  
           [0023]    3. Max. firing limit 2300° F. (1260° C.)  
           [0024]    4. Max. firing limit 1976° F. (1080° C).  
           [0025]    Zinc Oxide influences the color in a glaze more than any other element. Generally, zincless glazes should not contain magnesium oxide. Some colors containing zinc are to be used in a zincless glaze. The zinc in the color is in a combined form and will not harm the color, but free zinc oxide in the glaze can destroy the color.  
           [0026]    5. Do not use zinc in glaze.  
           [0027]    6. May be used with zinc or without zinc.  
           [0028]    7. Zinc not necessary, but gives better results  
           [0029]    8. Best results with no zinc.  
           [0030]    Calcium Oxide content as calcium carbonate should be from 12-15% for best color development. Adding the molecular equivalent of calcium oxide with wollastonite, a natural calcium silicate, often gives better uniformity. The increased silica from the wollastonite must be subtracted or the glaze will have a poor surface.  
           [0031]    9. Glaze must contain from 6.7 to 8.4% CaO (12-15% CaCO 3 )  
           [0032]    Metal to Metal Oxide Conversion Key for Color Composition Charts  
                                                           Al   Aluminum Oxide   Al 2 O 3             B   Boric Oxide   B 2 O 3             Ca   Calcium Oxide   CaO           Co   Cobalt Oxide   CoO           Cr   Chromium Oxide   Cr 2 O 3             Fe   Iron Oxide   Fe 2 O 3             Mn   Manganese Dioxide   MnO 2             Ni   Nickel Oxide   NiO           Pr   Praseodymium Oxide   Pr 6 O 11             Sb   Antimony Oxide   Sb 2 O 3             Si   Silicon Dioxide   SiO 2             Sn   Tin Dioxide   SnO 2             Ti   Titanium Dioxide   TiO 2             V   Vanadium Pentoxide   V 2 O 5             Zn   Zinc Oxide   ZnO           Zr   Zirconium Dioxide   ZrO 2                        
 
           [0033]    Refractory metal oxides are metal oxides stable in air at a temperature of at least 1600° F., preferably at least 1800° F., more preferably at least 1976° F, most preferably at least 2700° F. Here, the term “refractory” means stable in air at temperatures of at least 1600° F., and “stable” means without significant color degradation after heating in air to the specified temperature and cooling to room temperature.  
           [0034]    Mesh is a way to define the diameter of a particle by the size of interstitial site in a wire mesh through which the particle will pass. For example, 200 mesh particles will pass through the interstices of a wire screen with 200 wires per inch. Since the particle size that will pass through a screen decreases with increasing mesh number, particles defined as 200 mesh will contain all those capable of passing through a 200 wire per inch screen and smaller. Two-hundred mesh particles contain 400 mesh, but not 100 mesh.  
           [0035]    Since mesh is not a direct measurement of individual particles, but a characteristic of those that can pass through a specific screen, it is best thought of as representing the average particle diameter of all the particles that pass through the screen, averaged. Fifty mesh particles preferably have an average particle diameter of from 254 to 297 microns. One-hundred mesh particles preferably have an average particle diameter of 122 to 149 microns. Two-hundred mesh particles preferably have an average particle diameter of 40 to 85 microns, more preferably 45 to 80 microns, and most preferably 50 to 74 microns. Four-hundred mesh particles have an average particle diameter of 5 to 47 microns, preferably 10 to 42 microns, and most preferably 15 to 37 microns. 
       
    
    
     EXAMPLES  
     Example 1  
       [0036]    Five grams of silver jewelry-metal clay was weighed and handled in accordance to information provided by MITSUBISHI MATERIALS CORPORATION. After shaping three separate five gram clay samples into pancake-like forms, 0.1 gram of refractory stain was added to the first, 0.3 gram to the second, and 0.5 gram to the third. Each sample was kneaded until the refractory stain was thoroughly distributed throughout the jewelry-metal clay. A droplet of water was added to ease kneading of the 0.3 and 0.5 gram stain addition samples.  
         [0037]    The jewelry-metal clay samples containing the refractory stain were each rolled into an oval sheet and weighed. The samples were allowed to thoroughly dry before firing, and their dry weights recorded.  
         [0038]    The samples were fired on an earthenware tile, dusted with clean alumina hydrate. The tile was stilted and placed in an electronically monitored electric kiln. The samples were fast-fired according to MITSUBISHI MATERIALS CORPORATION&#39;s specifications (1650° F. for two hours). The kiln was allowed to cool before the samples were removed. The fired samples were weighed and the weights recorded.  
         [0039]    The samples were successfully colored with the color of the chosen refractory stain. The color was perfectly distributed. The sample containing the highest concentration (0.5 gram or 10% by weight) of refractory stain provided a darker colored silver article. The sample containing the lowest concentration (0.1 gram or 2% by weight) of refractory stain provided a lightly colored silver article. The resultant articles were malleable, like uncolored jewelry-metal clay sintered articles. The resultant articles demonstrated shrinkage, like uncolored jewelry-metal clay sintered articles, but showed no additional deformation or loss of detail in comparison to uncolored articles.  
       Prophetic Example 1  
       [0040]    Five grams of gold jewelry-metal clay is weighed and handled in accordance to information provided by MITSUBISHI MATERIALS CORPORATION. After shaping three separate five gram clay samples into pancake-like forms, 0.1 gram of refractory stain is added to the first, 0.3 gram to the second, and 0.5 gram to the third. Each sample is kneaded until the refractory stain is thoroughly distributed throughout the jewelry-metal clay. A droplet of water is added to ease kneading of the 0.3 and 0.5 gram stain addition samples.  
         [0041]    The jewelry-metal clay samples containing the refractory stain are each rolled into an oval sheet and weighed. The samples are allowed to thoroughly dry before firing, and their dry weights recorded.  
         [0042]    The samples are fired on an earthenware tile, dusted with clean alumina hydrate. The tile is stilted and placed in an electronically monitored electric kiln. The samples are fast-fired according to MITSUBISHI MATERIALS Corporation&#39;s specifications (1830° F. for two hours). The kiln is allowed to cool before the samples are removed. The fired samples are weighed and the weights recorded.  
       Prophetic Example 2  
       [0043]    A five gram sample of finely ground silver is weighed. One-half gram of refractory stain is added and thoroughly mixed with the silver powder. The powdered mixture of silver and refractory stain is pressed into a cylinder and fired in an electronically monitored electric kiln at 1470° F. for thirty minutes. The kiln is allowed to cool before the sample is removed. The colored silver mass is then removed and could be shaped into the desired item with hand tools, machine, or die. The colored silver could also be hammered or drawn into wires.  
         [0044]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.