Jalima, the aluminium baking foil with soda and boiling water works just as well as the plate and is better for large items. All items need to be in contact with the aluminium foil. The plate is a bit small (yes, I have one, too)
I did a little training with a museum conservationist who said that silver should never be cleaned with abrasives, except as a very last resort, as it's soft metal and easily rubbed away. She started with white spirit on a cotton wool swab, an impregnated cloth for more stubborn bits and an abrasive paste as a last resort!
She'd never heard of the foil and soda method but I've used it a lot and it works well.