I have used acid to get an interesting and uniform finish on
gold by first masking off the areas I didnt want exposed with
varnish. Then I immersed the piece in aqua regia (four parts
hydrochloric - one part nitric) for a few minutes. When the depth
was attained, I then electropolished the piece using the dyna-pro
system at 2 volts. This gave a very uniform color with a grainy
texture and it was bright… I’m not sure this is what you are
wanting, but you might try it on a scrap piece of gold.