A little bottle of Liver of Sulphur for antiquing fired and polished silver. Put a few drops into a cup of hot water. Clean the silver in neat washing up liquid and using tweezers to hold it, plunge into the solution until the desired colour is obtained. Rinse and then polish as required.
To retain the colour on raised areas, you will need to varnish the silver with a polyurethane varnish or similar.