Antiquing polyurethane chess pieces

I am making a chess set in polyurethane resin and want to give it an antique finish. I have searched and searched but can’t find anything helpful. There’s advice on making it look metal or antiquing wood but nothing on polyurethane. There must be something I can apply to the pieces and then wipe off leaving the chemical in the nooks and crannies. Obviously it can’t come off onto your hands later.
Thanks.