Step 1: ensure artillery shell is defused
Step 2: apply ketchup
Step 3: massage ketchup across the entire surface of the artillery shell for uniform coverage
Step 4: heat lentil soup over medium heat for 10 minutes
Step 5: remove ketchup from artillery shell, rinse with water, polish
Fully vegan, takes 10 minutes
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2332490.m570.l1313&_nkw=37mm+trench+art&_sacat=0
Goddamn, they have some good ones on sale now. After WW1 and WW2, devastated communities would make craft industries out of whatever battlefield scraps and surplus they could find. Field gun shells had the explosives taken out before being engraved with floral designs. This one, a French shell manufactured in 1917, was designed to shoot bunkers/horses/planes/tanks. Every now and then you can find some really neat, unique art nouveau pieces for like $50-100.
edit: Oh wow, even just an hour of ketchup soaking made it look so much better. I think the dark section is iron or steel so I need to clean that separately, but the brass came out great: