Lots of method for cleaning silver , talesof .
Along with what cogar & KC said , ash is an abrasive .
The gentlest I know of is using Orvus Wa ( a vet. soap 'cow shampoo' ) .
It's available from vet & farm suppliers , as well as from commercial cleaning/janitorial suppliers .
Conservators use this , also folks in the fire-smoke-damage restoration/repair business .
Virtually every silver polish , cleaner , electro-chem , manual/machine buffing method removes silver .
Orvus Wa simply cleans it with a gentle detergent (provided that a person does not go ape with the process) , but it's repetitious & labor intensive .
On-line silver forums have a lot of yakking about polishing/cleaning methods too , such as :
925-1000.com , smpub.com , silver-collector.com .