Niage is an important Japanese patina, and one of the most basic. It has been used as the base color on copper and copper alloys for centuries, and today it is also used as a final patina. As is true of all the recipes given here, these proportions are general guidelines, and experimentation is encouraged. A wide range of colors can be achieved by changing the concentration, proportions, or the time of exposure.
Grind the chemicals, one at a time, in a mortar and pestle until they are reduced to a fine powder. Heat the water, then stir in the copper sulfate until it is completely dissolved. Add the rokusho , again stirring until the powder has been completely absorbed. The copper sulfate takes longer to mix than the rokusho . Some people recommend adding a Japanese plum (umeboshi) to increase the red tones. It is best to heat the solution in a copper pot. If using glass, put a piece of copper in the vessel to supply additional copper to the solution.
|Immersing work in niage solution|
The finished color will depend on the duration of immersion, the proportions of ingredients, the temperature of the solution, the thickness of the metal, and whether the solution is applied to cast or chased work. In general, niage produces this sequence of colors, in which high-copper alloys (e.g., bronze) tend to fall toward the right-hand end of the scale:
Straw yellow > Gray-brown > Rust > Brick-red > Liver-colored > Dark brown
Use the recipe on the preceeding page to create a gray-brown, bronze-like patina on copper. To achieve a darker brown, make a more concentrated solution by using 15 grams each of copper sulfate and rokusho. [See Samples]
When brass objects are heated in niage solution at a low temperature the resulting patina will be pale green. If heated to a high temperature, the color will be ochre. [See Samples]
The niage solution will turn shibu-ichi light gray to dark gray. To make the color darker, add a small amount of shaku-do to the alloy. [See Samples]
To achieve other colors on shibu-ichi, it is first necessary to bring the silver to the surface. This is done by heating the finished piece in a soft flame, just to the point where it oxidizes, then immersing it in pickle . Repeat several times and you will see the work take on the appearance of silver. This layer does not respond well to patina chemicals, and can be selectively abraded away with sandpaper or pumice to achieve a feathered edge between colors. Heat the work in a niage solution to a temperature of about 50-60Â° C (122-140Â° F). The alloy will take on a reddish color, and when left in the simmering solution for a longer time, the color will change to a lovely gray. During the process, the surface will reveal a beautiful crystal structure, a peculiarity of this popular alloy.
To create a matte black patina, immerse the work in a warm niage solution. During this process, it is likely that a random pattern of red dots will appear. To color over these, dilute the solution and boil the work for a while longer until the surface achieves a uniform black color. There are reports of metalsmiths pickling their work in a strong sulfuric acid bath immediately before using the niage solution on kuromi-do. [See Samples]
Safety Note: This solution is safe to touch, but you should wash your hands thoroughly when the work is done. The vapor is also safe because only the water evaporates, not the chemicals.
Su-tanpan is another traditional patina that is normally used as a base upon which other patinas are applied, but it can also be used as a patina color all by itself. The results can range from light brown to gray to dark brown, depending on the strength of the solution and the length of time the solution is in contact with the metal. [See Samples]
Grind the copper sulfate and salt in a mortar and pestle to create a fine powder. Mix these powders together well, then gradually add the vinegar. Pour into a glass or plastic container, mark it with the name, ingredients, and the date it was mixed.
Su-tanpan is most often described as a base for copper, but it also creates a dark gray patina on silver. Use the recipe given above, and immerse the work until a uniform color appears. In most cases, the patina is polished off raised areas to create contrast between the light colored metal and the darkened recesses. In Japan this is traditionally done with baking powder. Other solutions used in Japan to darken silver include tincture of iodine and a sulfur-based product called muto-happu.
|Apply the solution by immersion or with a brush|