Patina on other

Depending on the sort of metal you have and whether the rust has left most of the plating intact, you can get chemical solutions to darken them. I've used the brass darkener (it's sold under a number of brand names and is phosphoric-acid based) available at Rockler Woodworking or Amazon in smaller 2oz or larger 8oz bottles and it worked quite well. Tricky part is figuring out what your metal is and testing a small piece to determine how long to soak it. Doesn't take long at all, just minutes if that.

Once you've done that, if it's a piece that will be touched often, use a non-shiny metal coating like ProtectaClear (not Krylon or similar, you want something without gloss) to keep the finish, because the darkened color will slowly rub off otherwise.

If its red rust, the base metal is steel. Not uncommon. My experience is that the crockpot trick works fine with solid brass hardware.