I get a lot of requests for metallic ink for letterpress. And I always have to answer with, "well..... it's not the best... you may be looking for hot foil stamping instead..." which, I don't do. The ink used on uncoated paper on letterpress just soaks in and it's hard to see any metallic.
BUT. I recently experimented with black museum board with metallic and check out these results:
They pop! The silver and gold against the black really shine. This made me sooo happy. Here comes more black and metallic!