How to Remove Yellowed Varnish From an Acrylic Painting

Build up a base of support underneath the canvas to avoid damaging it during varnish removal. Lay the yellowed acrylic painting face-up on a clean table. Stack up strips of wood underneath the inside of the back of the painting to meet -- but not distort -- the canvas surface. Lift off the canvas carefully. Cover the stacked wood with a layer of plastic wrap then replace the canvas on top.

Clean the surface of the varnished painting with degreaser. Saturate a clean cotton rag in degreaser and fold into a square. Lightly rub the fabric square over the entire painting until the bottom of the square is dirty. Fold the square again and use a new, clean side to continue cleaning. Repeat until all the surface dirt is gone.

Test the varnish remover on a small area of the canvas. Put on rubber gloves. Saturate a clean cotton swab with the solvent. Roll the wet swab gently, without pressure, over a corner. Wet the second side of the swab and roll over the same area. Check the painting to see if the varnish came off without damaging the paint. Check the swab for any paint residue. The right remover will leave only varnish residue on the swab and will clean the varnish off the acrylic paint completely. Do not use a remover that causes the varnish to become milky or removes any paint.

Saturate a clean cotton or polyester square with the varnish remover. Lay the white cloth evenly over a corner of the varnished painting. Remove after three minutes and place in a plastic bag. Saturate the second square with solvent and dab over the same area of the painting lightly to remove the yellowed varnish. Repeat, using two new squares of saturated cloth for each area covered until the painting is completely cleaned.

Check the surface of the cleaned acrylic painting for tacky areas; a gummy surface indicates that some of varnish remains. Repeat the process described in Step 3 until the acrylic painting is entirely varnish-free and is no longer sticky to the touch.