The process of patination is associated with copper, bronze, and sometimes brass. It is a film formed on the surface of the metal, either through natural exposure to the air or by treatment with acids or chemicals, which alters the color of the metals. Oxidization occurs when metal is exposed to air and damp, allowing the sulfur content that is present in the atmosphere to discolor and blacken the metal.
Oxidization also occurs when an oxidizing flame is used to heat metal. The heat from the flame combines with the oxygen in the air and forms a film of oxide on the surface of the metal. The process can be simulated chemically by placing metal into "liver of sulfur" or a potassium sulfide solution. The chemicals in the sulfur solution combine with the metal to form a colored surface.
If liver of sulfur is used in a hot solution, standard silver and gold’s that are less than 18 carat will turn black. A few drops of household ammonia can be added to give an even deeper black. If the solution is warm, rather than hot, the colors will range from yellow-gray, through to some wonderful shades of blue, pink and purple. These colors are not, however, stable unless a coat of lacquer or beeswax is applied. When it is used cold, liver of sulfur will color copper, but it will have little or an unpleasant effect on silver.
Metal that is to be patinated or oxidized should be completely clean all residues of flux must be removed, for example and if it has been polished, all traces of polish must be removed together with any finger marks.
The piece is suspended in an oxidizing solution by means of a copper wire. The solution is most effective when it is deep yellow in color, and if it is being used hot, it should not be boiling. Mix only the amount you will need for one application because the solution quickly spoils. The solution can also be painted onto specific areas with a fine paintbrush, and you will find it easier to work if the metal is warmed slightly before you begin.
When you have achieved the color you want, rinse the piece thoroughly because any solution that is left on the metal will continue to work.
If you need to remove the color, you can scratch or brush it off, or you can heat the object and pickle it, or you can simply polish it. Other coloring effects can be achieved by the use of chemicals.
Remember that all chemicals should be stored safely, preferably under lock and key.
Writer – Jinks McGrath