Chemical Blacking liquid for Brass
Also works on copper and bronze.
Fast-acting liquid used by gunsmiths and industry to blacken or antique brass, copper and bronze parts. Easy to apply with no dimensional change. Often used to mark cartridge cases to identify loads. Excellent for blackening name plates, plaques, castings, sculptures and other home, workshop and hobby uses. Colour varies depending on alloy and can be highlighted if desired.
Then use a dewatering fluid such as wd40 or even beeswax to seal the product.
Very simple process