Permanent colors on tin metal

We are an angling products supplier in Stourbridge, England and we manufacture non toxic fishing weights made from Tin ( Sn ) We need to apply a green or brown permanent color to the surface, preferably without electro plating, Is this possible at a reasonably cheap rate using say, a chemical process ? We have asked some professionals around here who say it is not possible, but one person says he knows of a process but will not divulge it to us. We need to process a couple of tons per year. Can anyone help ?

Bronze brown patina for tin/pewter:
3 gm ammonium chloride
12 gm copper acetate [affil link]
20 gm vinegar ⇦in bulk on eBay or Amazon [affil link]
1 lit water
You must clearcoat finished objects!Hope it helps and good luck!