What is your best product to blacken brass? A What is your best product to blacken brass? The best product for blackening brass is the JAX Black for Brass, Bronze and Copper. Category: Specific Looks and MaterialsIf you like this, share it Post navigationPrevious post: Does the Jax Iron Steel and Nickel Blackener work on stainless steel?Next post: I am looking to patina a material I believe to be zinc based, Zamak 5. Will any Jax products either darken it in a similar manner to cold blue on steel, or, alternately, make it iridescent and colorful?