I know this will sound out of line as this is a metal forum. but unless your doing copper or copper based metals or stainless steel the problems become pretty heavy when you get to longevity with water or moisture present. The surfaces or seals become the only positive solutions on most other metals and many are not all that permanent. I would immediately be looking towards media that don't present the problems. Like the fiberglass or exterior plastics. A big subject here but also one I've dealt with for 40 years already. In addition coloring and all is no problem as super epoxy paints (such as used on battleships) come in a full range of colors and mixtures and with these you can even start to do some metalized coatings over it all. Contact me direct on email and I'll send a few illustrative and picture files that are too large for me to figure out how to do it here. (Believe me I've tried, tired of wasting time here.) Using the media then becomes one either fabrication or castings or both. Your choice. bpfink1@mac.com