To remove tarnish from brass we used an old aluminum baking pan, laid the brass hardware in, added washing soda (or you can use baking soda) and then adding boiling water. Allow two minutes or so otherwise a reverse action may occur and you will have to do it again. The chemical reaction allows tarnish to vanish. for heavily tarnished items repeat. Mine were black with age 84 years – never cleaned so I finished off with Brasso (fab product) which cleans and polishes.