[lexluthier]

I wouldn't use etchant, sometimes the plating is so shitty these days you can eat right through the nickel if you leave it in too long. I've used muriatic acid fumes and also phosphoric acid fumes. Always rinse the acid off the parts with water after aging.

Wear goggles and gloves and use it outside, that stuff is hazardous! I've used a cardboard box with a tray of acid on the bottom, seems to work for me.