Try Ferric nitrate see the link below:

http://gossdesignstudio.com/sandranoblegoss/etchingster.html

10 ml sulfuric acid 100 ml saturated aqueous solution of potassium dichromate 2 ml saturated aqueous solution of sodium chloride Etch seconds to minutes, 1:9 dilution with distilled Water. Possibly without sulfuric acid.

Also:

https://vacaero.com/information-resources/metallography-with-george-vander-voort/1251-metallographic-procedures-for-precious-metals.html

The ferric nitrate is a good option for etching of silver.

Please check the attached file for more details.

Gentlemen, thank you very much for your help. Ferric nitrate works pretty well. Vladimir, we were able to get ferric nitrate from our collegues so we tested it first. Surely, your suggestion would work as well.