Good art has been thought to be the rich man's investment. Actually it's an excellent investment for anyone. In the last twenty years it has surpassed the stock market in appreciation. However, like the stock market, one can make a hefty investment on an up and coming artist, but not realize the potential gain until years later. A very good reason to keep an oil painting in top condition, both cleaning and restoring when necessary.
The rate at which an oil painting becomes dirty depends on the atmosphere of it's location. Smoke, dirt and clouded varnish contribute to a dull, muted appearance. Many would argue that the restoration of oil paintings should be left to professionals. The various steps they would take, or if you decide to do the work yourself, are as follows:
1. Deframing
Working on a table or workbench, cover a thick piece of foam, slightly larger than the frame, with a soft towel. You don't want to damage the frame or the painting and you'll be glad you took extra precautions from the beginning. Start by vacuuming the back of the frame to get rid of any loose dust.
Next, remove any nails holding the frame backing or painting into place with a pliers and chisel. Place the chisel under the pliers as to avoid damaging the frame with indentations. You will want to replace the nails into the same location when you resecure the painting after cleaning. A smart trick is to place the nail on a piece of masking tape, flipping the tape over on top and then mark with a pen the location (right top, left top, center bottom, etc.). You will also want to mark the top of the frame with a piece of masking tape so that everything fits back together properly. Gently vacuum the inside of the frame and the painting.
2. Removing the Foxing
A light mildew may have formed, called foxing. If this is the case, you will want to get a cleaning agent containing sodium hypochloride. It comes in such brands as Mould Rit or Exit Mould and can be purchased at an art supply store, framing shop or arts and crafts store.
Pour some of the cleaning agent onto a cotton ball and gently rub the affected area, rinse with clean water and a soft sponge. This portion of the restoration should be done quickly as it is not good for the painting to have the mildew cleaning agent on it for too long a period of time.
3. Cleaning
A trick for light cleaning is to lightly rub with a half of an onion. The chemical reaction between the onion and the oil paint combined renders and excellent cleanser that can be further benefited with a few drops of lemon juice.
For a medium cleaning use a mild detergent such as Ivory dish soap and tepid water. Use a soft sponge and wring it out as completely as possible before gently rubbing the oil painting. Use a separate sponge for rinsing. When finished, again rinse the entire surface several times, making sure all of the detergent is removed.
For a dirtier painting, sodium carbonate may have to be used. In a cup of tepid water drop just a pinch of sodium carbonate, stirring until it dissolves. Using a cotton ball try the solution on the end of a corner. Make sure the cleaning agent is not picking up any color from the oils. If all is working well, clean the entire painting and again rinse several times well with a clean sponge and tepid water.
4. Removing Varnish
When an oil painting is still very clouded and dull even after a thorough cleaning, it may be necessary to remove the old varnish, reclean the painting and varnish it again. Methylated spirits are used on a cotton wool pad. A second pad dipped in turpentine diluted with linseed oil ready to arrest the methylated spirits if needed. Watch the darker colors as they dissolve quicker than the lighter colors. Be sure to check the cotton wool pad every time an area is cleaned to make sure color is not being removed. Once the paining is completely cleaned and dry a new coat of varnish may be applied using crisscross movements with a flat brush.
5. Flaking and Blistering
When flaking and/or blistering are visible on the oil painting a mixture of damar resin and beeswax can be warmed to 160 degrees and applied warm to the area with a brush, careful not to loosen and remove any flakes. When dry, reheat the mixture and apply it to the back of the painting in the same area. With a piece of clean paper, use a warm electric iron over the back area of the painting to solidify the paint. Epoxy can also be used to repair such painting maladies.
6. Tears and Holes
By applying a new piece of canvas to the back of the painting, using the same damar resin and beeswax mixture as in repair of flaking or blistering, a hole or tear can be repaired. This should be done after the painting is completely cleaned as the area of the tear or hole will need to be retouched with oils at the front of the painting where the new canvas shows through.