The surface of metals may be colored, a patina added either chemically or with heat. Patinas are generally achieved by causing the metal present to react with another element. It may be the air forming oxides or another chemical added to bond molecularly with the surface. A few pseudo-patinas are simple coatings on the metal's surface.
Preparing the Surface
A key to achieving a good patina is to work with an antiseptically clean surface. A number of methods; will give good results.
Existing oxides should be removed in a pickling or bright dip solution. The piece may then be scrubbed with powdered pumice to remove dirt, Grease residue may be removed with a vigorous scrubbing in a strong detergent and water solution, Ultrasonic cleaning is effective if the piece contains hard to reach recesses. A final rinse in hot clear water will remove residual cleaning agents.
Physically altering a metal's surface will also prepare the surface. Read blasting works well if a matte finish is desired. Scratch brushing often follows the first application of a patina, with reapplication the effect will be greater. A scratch brush will clean the surface and give a satin appearance to the patina.
Application of patinas should be done immediately after cleaning. Prolonged contact with air will contaminate the surface of most metals. Zinc should be kept underwater if there is any delay in coloring as it will oxidize rapidly in the air.
Protecting a Patina
Due to the possibility of continued color change, once a desired patina is reached, many pieces will require Protection from further reaction. Sealing the surface from the environment may be accomplished with either a lacquer or wax finish.
Lacquers provide good protection but may eventually chip, Use a high quality product to avoid later discoloring. Clear nail polish also works for small areas. It may need to be thinned to provide an even surface.
Paraffin or bees wax are also used to protect the surface of metals. Museum Wax and Renaissance Wax are high quality commercial preparations. Wax may be applied directly to the surface, or it may be thinned. Mixing the warmed wax in a 4/1 ratio with turpentine will provide an easy-to-apply paste. Avoid commercially prepared paste waxes; they may contain chemicals that will further color the piece. A waxed finish may not hold up to wear and will certainly be attacked by soaps and detergents.
Copper Plating
One method of coloring is to copper plate. Metals that are difficult to oxidize (brass, gold, and platinum) may be plated, by galvanic reaction, in copper saturated (blue) pickle solution. Submerging; the piece, suspended by an iron or steel wire, will result in a thin layer of copper which will accept oxidizing action. Because it is thin this plating will not withstand wear. It will work well in recessed areas. After plating and coloring, the raised areas may be restored with in abrasive polish.
Formulas Compiled by: Alexander Soroka State University of Iowa M.F.A. Thesis Project
The following patina formulas are but a sampling of the hundreds in existence. The formulas selected illustrate the wide range of application methods employed as well as a rich variety of colors. The first 30 formulas listed are represented on a supplemental sampling chart to designed for use as a visual text-book.
| 1. Light to Dark Brown (basic brown) (Clarke) |
| Ferric nitrate | 1/2 teaspoon |
| Water | 1 pint |
| A hot process, transparent color. Fresh mixture necessary for each coloring. Preservative is optional. |
| 2. Antique Green (Miller) |
| Cupric nitrate | 40 grams |
| Ammonium chloride | 40 grams |
| Calcium chloride | 40 grams |
| Water | to make one liter (approx. 1 qt.) |
| A cold process, opaque patina. Frog green results after several applications, 1/2 hr. Intervals. Color is not satisfactory alone. Combines well with most brown and black cold process patinas. Preservative is optional. |
| 3. Matte Brown (Rich) |
| Barium sulphide | 1 ounce |
| Potassium sulphide | 1/4 ounces |
| Ammonia | 2 fluid ounces |
| Water | 3 to 5 quarts |
| An excellent cold process, opaque patina that darkens immediately after application. The matte color is best without a preservative, although choice is optional. |
| 4. Yellow Green (Clarke) |
| Ammonium chloride | 7 parts by weight |
| Copper acetate | 4 parts by weight |
| Water | 6 parts by weight |
| A cold process, heavy opaque patina that takes effect after several applications. Preservative is optional. |
| 5. Rust Brown (Payne) |
| Ferric nitrate | 3 ounces |
| Perchloride of iron | 2 ounces |
| Water | 1 to 3 quarts |
| An excellent, cold process opaque patina. It achieves immediate effects. Preservative is not necessary. |
| 6. Blue (Miller) |
| Sodium hyposulphate | 60 grams |
| Nitric acid | 4 grams |
| Water | 1 quart |
| A transparent, dip process patina. A preservative is necessary. |
| 7. Light Green (De Marco) |
| Ammonium chloride | 16 units |
| Sodium chloride | 16 units |
| Ammonium hydroxide | 16 units |
| A cold process, opaque patina which should be applied at 12 hour intervals for several days. A preservative is optional. For deeper green add 16 units of copper sulphate. |
| 8. Brown to Black (Clarke) |
| Antimony sulphide | 2 parts by weight |
| Sodium hydroxide (lye) | 4 parts by weight |
| Water | 256 parts by weight |
| An excellent, hot process, semi-opaque patina. Color appears immediately after application. This patina can also be applied cold. A preservative is necessary |
| 9. Basic Brown 70 Black (Clarke) |
| Potassium sulphide a grape size lump (crushed) | Water 1 pint |
| A transparent, hot or cold process patina that can be used only once, otherwise the solu710m becomes neutral. Preservative is optional. |
| 10. Purple (De Marco) |
| Over a copper nitrate, hotprocess patina (#16) apply a coat of saturated potassium ferrocyanide to the heated bronze. A preservative optional. |
| 11. Despiau Black (De Marco) |
| A. Acquire a light green base with a hot process, copper nitrate solution. (#16 ) |
| B. Then apply a light coat of brown with a ferric nitrate patina solution. (#1) |
| C. Mix batch (A) of |
| Ammonium sulphide | 1/2 teaspoon |
| Ferric nitrate | 1/2 teaspoon |
| Water | 1 pint |
| D. Mix batch (B) of |
| Potassium sulphate | 1/2 teaspoon |
| Ferric nitrate | 1/2 teaspoon |
| Water | 1 pint |
| E. Then apply solutions to a hot bronze surface in the following fashion until the Desired effect is achieved. Apply batch (a) then water, apply batch (b) then water, Apply batch (a) etc. |
| 12. White (Soroka) |
| Diluted liquid gesso is painted to the surface of the metal and buffed down slightly With steel wool or a brush as desired..powdered colors can be added to the gesso. A preservative is not necessary although a light spray of acrylic can be used on Patches of exposed bronze. |
| 13. Straw Yellow (Soroka) |
| Home made ferric nitrate grounds | 1/2 teaspoon |
| Water | 1 pint |
| Ferric nitrate is made by filling a pint jar half full of rusty nails and then pouring nitric acid over these nails until 1/4 of the jar is filled, this should be done outdoors for the resulting fumes are highly toxic. The mixture gets better with age, however, the patina solution can only be used once. A preservative is optional on this transparent patina. |
| 14. Nickel Plate |
| Nickel sulfate | 24 ounces |
| Ammonium chloride | 3.3 ounces |
| Boric acid | 4.0 ounces |
| Water | 1 gallon |
| 110 degrees to 140 degrees F. |
| 25 to 50 amps./sq. ft. |
| Varied effects can be achieved by blocking out areas with lacquer, as a result cool and warm areas are achieved on the same piece. |
| 15. Peacock Blue (Krause) |
| Sodium thiosulphate | 150 g./1. |
| Lead acetate | 25 g. |
| Cream of tartar | 30 g. |
| Water | 1 liter |
| A intense, dip process, transparent patina. Immerse object from 20 to 30 minutes. A preservative should be applied immediately after the object is removed and dried. |
| 16. Basic Green (Clarke) |
| Copper nitrate | 1 teaspoon |
| Water | 1 pint |
| A hot process, semi-transparent patina. A fresh mixture is necessary for each coloring, preservative is optional. |
| 17. Basic Blue-Black (Clarke) |
| Ammonium sulphide | 1 teaspoon |
| Water | 1 pint |
| A hot or cold process, transparent patina. A preservative is optional. |
| 18. Chromium Plate |
| Chromic acid | 53 ounces |
| Sulphate | 0.53 ounces |
| Water | 1 gallon |
| 120 degrees F. |
| 200 amps./sq. ft. |
| Varied effects can be achieved by blocking out areas with lacquer, as a result cool and warm areas are achieved on the same piece. |
| 19. Blue-Green |
| Bronze object should be buried in sawdust, saturated with vinegar for several days, with additional sprinkling of vinegar if necessary. The patina is heavily opaque, a preservative is optional. |
| 20. Antique White (Soroka) |
| Bismuth nitrate | 2 teaspoons |
| Water | 1 pint |
| Potassium sulphide | a pinch |
| A excellent, semi-opaque, hot process patina. The object should be slightly oxidized with the torch before the solution is applied. Ferric nitrate or copper nitrate be substituted for thepotassium sulphide, depending upon the effect desired. A preservative is not necessary. |
| 21. Brown (Clarke with Variation) |
| Sodium thiosulphate | 1 part by weight |
| Ferric nitrate | 8 parts by weight |
| Water | 128 parts by weight |
| An excellent cold process, opaque patina. Works well without a preservative. |
| 22. Verde |
| Copper sulphate | 6 parts by weight |
| Ammonium chloride | 4 parts by weight |
| Sodium chloride | 4 parts by weight |
| Zinc chloride | 1 part by weight |
| Glacial acetic acid | 3 parts by weight |
| Water | 128 parts by weight |
| A dip process patina immerse object in solution for a few minutes, then remove. Repeat until a color appears. A preservative is optional |
| 23. Metallic Blue-Black |
| Yellow barium sulphide | 1 part by weight |
| Water | 120 parts by weight |
| A dip process, semi-opaque patina. Immerse object in solution overnight at normal temperature. A preservative is necessary. |
| 24. Japanese Brown |
| Copper sulphate | 5 ounces |
| Cupric acetate | 5 ounces |
| Copper carbonate | 5 ounces |
| Water | 1 gallon |
| A transparent, dip process patina. Preservative is optiona |
| 25. Wine Vinegar Green (De Marco) |
| Red or white wine vinegar | 1/2 liter |
| Water | 1/2 liter |
| Ammonium hydroxide | 1 tablespoon |
| Muriatic acid | 1 tablespoon |
| Sodium chloride (salt) | 1 teaspoon |
| Ammonium chloride | 100 grams. |
| An excellent, cold process, opaque patina. Apply solution for several days at 12 hour intervals. A preservative is optional. |
| 26. Fire-Oxide Bronze |
| Bronze casting as it appears when broken from a plaster investment and buffed slightly with a wire brush. |
| 27. Raw 85-5-5-5 Bronze |
| Bronze as it appears after a cleaning in a diluted nitric acid pickle. 85% copper, 5% tin, 5% lead, 5% zinc |
| 28. Heat Oxidized and Reduction Flame Patina. |
| Raw bronze as it appears after being heated' with an acetylene torch using a heavy reducing flame. When a black coating appears it is buffed down with steel wool and a soft cloth. A preservative is optional. |
| 29. Apple Green |
| Sodium chloride | 5 parts by weight |
| Ammonia | 4 parts by weight |
| Ammonium chloride | 5 parts by weight |
| Glacial acid | 4 parts by weight |
| Water | 32 parts by weight |
| A cold process, heavy opaque patina. Preservative is optional. |
| 30. Transparent Black (Gadberry) |
| Chlormoauric acid crystals or cold chloride | 1/2 gram |
| Water | 100 ml. |
| For immediate results paint or spray (with class atomizer) one coat of this solution. Can also be used as a dip. A preservative is optional. |
By Alexander Soroka – © 2004
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