‘Platinol’ Oxidising Solution is very good and widely available, I have discovered some very nice finishes with this product, including using a frosting brush afterwards.
Use protective gloves and goggles because it will stain your fingernails.
Warm the piece up first with a flame or very hot water. You will see an instant result, if you don’t warm it up but it takes longer and the result is not the same.
Rinse the piece off thoroughly in cold water, otherwise it will contaminate your gloves and other pieces if you touch them immediately after.
Don’t wash off your oxidised piece in the ultrasonic or you will contaminate it for other users.
In his 40 year career Stephen M Goldsmith has worked for clients from Garrard’s the Crown Jewellers to celebrity jewellery designer Theo Fennell and restored the silverware of many eminent patrons including the Royal Household.