Well, if you are not pressed for time, you might consider patinating silver using an anti-dandruff shampoo containing selenium sulphide (American sulfide).
The darker sterling dome was immersed in a small quantity of head and Shoulders Scalp Relief, currently available at larger branches of Sainsbury and at high street chemists.
It took 48 hours to reach this degree of blackness and at the end of that time it was rinsed away under running water, just like…..shampoo. Dennis.