I thought about Silver nitrate, but that is very expensive, and personally, I would do the "silvering a flask" reaction, take Silver nitrate, add ammonia (drop wise) creating a black precipitate.
Stop adding ammonia once the precipitate formed, now switch to another ammonia solution, this time with some indicator, to make it red. Add it until it dissolves. Now, add a solution of dextrose and KOH to it. stopper and shake the flask. A silver (hopefully, not redsilver) mirror forms. Jesus's blood has turned some nasty brown/gray stuff to a silver mirror. (makes a nice keepsake too, train the solution and rinse the inside with some kind of a sealing solution like a clearcoat.)