I have a solution that is comprised of the following that I use to electroplate a brass dial for watch making purposes.
The nickel plating solution I have is:
-Water
-Nickel (II) Sulfate (45-50% by weight)
-Zinc Sulfate Heptahydrate (20-24%)
-Ammonium Thiocyanate (20-23%)
-Zinc Chloride (1-3%).
I want to imitate a patina that is found on watches from the 1950s where the black nickel electroplate turned brown.
Knowing what is in the electroplating solution, is there anything i can do chemistry wise to force oxidize the black nickel post plating to mimic the
browns in a somewhat controlled manner?