Paintings should be framed in a frame with no glass (open face) or double matted with an air space between the painting and the glass.
This will prevent the paint from sticking to the glass.
Paintings can be cleaned with a spray on wax based cleaner (such as Pledge or Pledge Wipes.)
Spray Pledge on a lint-free towel. After the foam settles, carefully clean the painting with the towel.