What would it rub?

[Мира]

Dear friends!
Please advise how to clean the painting at home?
Bought a hefty canvas 19th century , oil on canvas , very dirty , as if it were eating and drinking, and indulge in other pleasures of life.
Do not show a picture of timidity, fear of new jokes .

Washed her some water , a sponge was black , the picture was better.
The English book on housekeeping 19th century painting recommend rubbing fresh cut potatoes ... like the proverb.

If you have some experience , not all the pictures it sends to the restorer , please share .

Thank you!