Don’t use a potato! This is not an effective cleaning method and it will leave undesirable residues on the surface. It’s best to use your own saliva on a cotton bud; roll the cotton bud carefully over the surface. However, if the oil painting doesn’t have a protective layer of varnish or if the paint itself is cracked, you will risk damaging the layers of paint. In this case, you should take the painting to a conservator.

Kind regards from Laura, paintings conservator