G'day; Ferric chloride will etch copper easily, but I don't think it
would be any use for etching silver. The act of etching is to use the
non metallic ion (example, chloride, nitrate) to dissolve the metal
to be etched. As silver chloride is insoluble in water, ferric
chloride won't work. But ferric nitrate will; the silver nitrate so
formed is indeed soluble.
Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ