It depends on the metals you want to dissolve. Nitric acid is likely to be the best universal reagent as most nitrates are water soluble, but beware it's not the easiest material to handle.
Dear c2sco,
The alloy to be etched / dissolved is Invar ( Which contains Nickel- 36% & Iron- Balance).Please advice the chemical for the same.
Thanks & Best Regards
Mehaboob P K