Dust the surface of the painting with a feather duster or soft dusting cloth to remove loose dust. Use canned air to blow across the surface to remove smaller particulates or stubborn dust. Watch for signs of loose paint and avoid blowing in those areas.
Blot the surface of water color and acrylic paintings with white bread. The bread will absorb oil and lift dust using staticcling. Ball the bread up and rub it gently on stubborn spots like an eraser.
Clean dirt and yellowing varnish from the surface of oil paintings with specialty cleaning solvents, available in art stores. Remove the painting from its frame and use a cotton swab to apply a small amount of the solvent to the paint along the edge of the painting where the frame will cover it to test for color fastness. It should take only dirt, if any color comes away on the swab, discontinue and take your painting to a professional restorer. Continue cleaning with the cotton swab until the painting surface is completely clean.
Cut a piece of thermoplastic film a little larger than the tear. Cut a patch of linen a little larger than the tape. Fold a piece of linen so that it is four thicknesses thick.
Plug in a household iron and turn it to the "linen" setting. Allow the iron to heat up. Test a hot iron by putting a drop of water on its face, when it sizzles, the iron is hot.
Place the painting on top of a table or counter with a towel below it. Position the thermoplastic film on the rib, with the linen patch centered over it and the folded linen on top of that. Press the hot iron on top of the folded linen. Allow the heat to penetrate until the thermoplastic shrinks and seals to the canvas.
Fill cracks or voids in the painted surface with a coat of gesso canvas sizer and primer. Use a flexible putty knife to apply the paste. Allow it to dry.
Mix paint in the correct color to match the area surrounding the damaged section. Use an art brush to paint over the gesso to blend the damaged area in.
Apply any highlights or shadows required to complete the image restoration. Mix shadows with your base color and a small amount of black paint, mix highlights with your base color and a small amount of white paint.