Need a green patina on steel

I need to spray several very large steel sculptures with something to turn them that funky green like old copper. Also I need to know what to spray down beforehand to keep the rust from bleeding through. I'm trying to make some of my work more attractive for a local business owner who is interested in selling my work, so it needs to be a long term solution. thanks in advance. : )

You must copper plate your sculptures, and then you can colour them like copper.

Good luck!

Immersion copper for iron and steel:
50 gm copper sulphate
50 gm ammonia ⇦ on eBay or Amazon [affil link] (25%)
1 lit water You must add some tartaric acid ⇦ on eBay or Amazon [affil link] (pH must be 3,5)! It can be sprayed or painted on your object!