The first step in cleaning an oil painting is to remove the paint from its frame. Make sure the frame is on a smooth surface to avoid damage. Once the frame is out, use a vacuum cleaner to clean the cracks where the paint meets the wooden stretcher. Be careful not to chip the paint.
The next step is to remove the mold. Using a cotton ball and sodium hydrochloride cleaner, gently rub the affected area of paint. Before proceeding, check the cotton ball to make sure the paint is not flaking off. Once the area is clean, wipe it off immediately with a damp sponge. Make sure to remove all the cleaning agent.
To clean a small amount of dirt and grime, use an onion cut in half. The potency can be increased by adding lemon drops. Do not allow the onion and lemon mixture to dry on the paint. Clean with a damp sponge. If the dirt still persists, move on to clean with a lemon detergent. A soft sponge with warm water should be used. Use as little water as possible. After cleaning, wipe off all the detergent.
For a higher level of dirt and grime, use soda ash. The concentration will need to be determined before using the solution on the entire canvas. The way to do this is to dissolve a small amount of sodium carbonate in warm water, then test the mixture on a corner of the pain with a cotton ball. Continue this process until the mixture removes dirt without stripping the paint. After cleaning, rinse the soda ash with fresh water or it will leave white streaks.
If the paint is so dirty, the above methods do not work, the next step is to remove the varnish. What is needed to remove the varnish is methylated alcohol, turpentine diluted with linseed oil, and several cotton balls. Use the cotton ball covered with methyl alcohol to remove the varnish. It is important not to go deep, to remove only the varnish and not the paint underneath. The method used to protect the paint underneath is after removing the varnish, use a fresh cotton ball covered with the linseed oil and turpentine mixture to stop the methylated spirits. Continually check the cotton ball to make sure the paint is not flaking off. If the paint starts to flake, use the turpentine linseed oil mixture to stop it.
After cleaning the paint it is necessary to re-varnish the paint. The varnish can be glossy or matte and should be applied in a crisscross pattern with a varnish brush. Let it dry.