John - if you are talking about silver, the finish is called a
iridescent patina. It is easily applied in the studio. My personal
formula is: one cup room temperature water, a pea sized bit of liver
of sulfur, iodized table salt and a bit of sudsy household ammonia.
Applying it cold makes it change colors slow enough that you can stop
it when you like. Stop coloring with a plain water rinse. Metal
should be clean prior to application. Works better on textured
But - it is not long term stable. It can be protected with silver
cloth or plastic bags. You cannot seal it - that changes the color
and dulls the iridescence.
You can simulate this effect with iridescent powders and sculpture
patinas but it doesn’t work on silver, it works on copper and bronze.
Sculpture patinas can be sealed.