Excerpt from “The Complete Metalsmith”
The following is quoted directly from "The Complete Metalsmith" by Tim McCreight
Liver of Sulfur (Potassium Sulfide)
This sulfur smelling yellow liquid is one of the most commonly used chemicals to darken metal. It will quickly produce black on sterling and copper, but it's capable of much more. By moving slowly through the development of the sulfide layer, a range of colors present themselves. They are not permanent enough for an exposed surface such as a ring shank, but they are satisfactory for pins, earrings, and pendants.
Liver of sulfur quickly loses its strength when exposed to air or light. For this reason, it is commonly sold in large chunks and kept either in a can or a brown glass jar. Break off just what you need and carefully seal up the reast.
Dissove a small amount of liver of sulfur in warm water. A pea-sized piece to a cup of water is usual. If the solution is too stong, the resulting sufide layer is brittle and will be easily chipped off. The solution may be warmed, but should never boil. The solution may be brushed on or the work may be immersed. I recommend the dip-rinse method to slowly create a wide range of colors. Work at the sink, warming the piece under a running stream of hot water. I dip the pieces briefly into the liver of sulfur solution then quickly rinse it off. This dip-rinse cycle will allow you to see the full spectrum of colors, which on sterling, runs from gold to brown to vermillion to blue to gray. A small amount of ammonia added to the solution will enhance the blues and a little baking soda will deepen the browns.
On copper, use a weaker solution and brass brush between each dip to create a purplish gray. It's especially importatnt that you remove all fingerprints before darkening copper. Liver of sulfur will have almost no effect on brass or nickel silver.
