[Bsteg]

         I am trying to develop a process to antique alloy-230 brass (70% copper, 30% Zinc) hardware. Right now I am using Potassium Persulfate (K[2]S[2]O[8]) to tarnish the metal at 130 degrees Fahrenheit.

          Also in the same bath I add some NaOH to make the solution very caustic. I was wondering why the process needs to be caustic?  Also is it possible to decrease the pH a bit so I can use less NaOH.

           I get inconsistent results, sometimes the color is light blue and sometimes dark blue (almost black).  I figured the reason was because the Potassium Persulfate is being consumed but I do not fully understand the basic equations. Does anyone understand the basic stoichiometry of the reactions? Also it does not seem that the NaOH is not consumed at all.



I found on another forum the predicted reaction:
Copper + Potassium Persulfate --> Copper sulfate + Potassium Sulfate
Zinc+ Potassium Persulfate --> Zinc sulfate + Potassium Sulfate

Also there seems to be a solid forming at the bottom of the tank after the tank cools, could this be the Potassium Persulfate precipitating out?