Thanks! Can't read the links but i think that ferric chloride is the same than iron perchloride.It must be tried.
I've not a great experience in etching but my daughter use it on brass jewels. On the other hand i use electrolysis to gilded and silvering antiques. I'm a bronze and silver restorer .
I've used bitumen of Judea diluted in turpentine to recreate some Art Deco etching on lightings copies. My daughter use also this technic for etching.