There are several things to consider when you are handling artwork. First, you need to make sure the value of the piece, if it is expensive, is documented!
From there, Annissa offers several different ways you can carefully clean affected artwork.
Also, don't go into this type of restoration work without some help and guidance from experts. She has some great places to look for education like this.
Have a question for Annissa? Shoot her an email at firstname.lastname@example.org.