Electro-Etching silver

I am wondering about the best parameters for electrolytic etching.
In my particular case I am etching silver, and the electrolytes I am
testing are ferric nitrate, nitric acid and phosphoric acid.

My reasoning is that there is, just like in electroplating, an
optimal voltage and current density for each of the electrolytes.

Anybody has some insight or ideas into this?

Thanks,
Andreas