I decided to experiment with a Japanese copper alloy called Shibuichi. They mix I used was 75% copper, 25% silver. Over time it tarnished, which is to be expected due to its copper content, however the tarnish turned this really ugly gray. I tried burnishing with a brass brush and it turned shiny but didn’t get rid of the colour. Is this tarnish inevitable? What can I do to prevent it apart from laquers?