There is no doubt about it, restoring an oil painting can be considered an art form. It involves a fair degree of know-how, patience and a delicacy of touch. How successful you will be in achieving a pleasing outcome will depend entirely on the condition of the painting, and how valuable it is. Before taking on any restoration projects, a beginner would be well advised to take advice from a professional.
Failing this there are some methods which can be used to clean and restore your painting at home or in the workshop.
The one golden rule that must be always remembered is: you should NEVER allow water to come into contact with your painting. It is generally assumed that water soluble oil paints are a fairly modern invention, but they have in fact been in use for many years. By allowing water to come into contact with the surface, you can ruin a valuable painting in an instant. If you attempt to clean your painting with soap or detergent and water, you run the risk of inducing a kind of milky white reaction to the oil paint.
You may not think that damping the oil painting down to take the worst of the dirt away, will cause much harm, but in fact if you dampen the canvas in any way, you may be in danger of causing the canvas to stretch, leading to bagginess to the picture. Water can be very intrusive and can seep into any imperfections or cracks within the paint and cause flaking. This kind of damage is very difficult to restore.
Oil paint is used in conjunction with many different mediums such as linseed oil and other agents that help to thicken or thin the pigments during use. The integrity of the painting could be seriously damaged by using any kind of thinners or alcohol as these will invariably react to the painting causing the pigment to dissolve.
Abrasives (such as the scratchy pads used for washing dishes) will also interfere with the integrity of the brushwork and promote flaking.
To get a good idea of how grubby your painting is, you can lay it flat upon a work top and dust it with a feather duster to get rid of any loose fluff and dirt. You can also use a vacuum with a soft attachment or piece of muslin secured over the end of your nozzle to avoid damaging the surface of the painting.
A good method to remove general grease and accumulated dirt is to use a piece of bread. This method is useful for cleaning old books too.
Lightly brush the bread against the surface of the painting and you should see the dirt being absorbed by the bread. As each piece of bread becomes grubby, exchange it for a fresh piece. When you are satisfied with the result, give the surface a flick with a soft brush to get rid of any loose crumbs.
Other home remedies include using a cut potato or an onion, to act as an astringent with a couple of drops of lemon juice. Use a dabbing motion over the surface of the painting to avoid too much dragging over the paint. As each piece absorbs the dirt and grease, exchange for fresh piece until the whole picture is clean. Always remember to do a "test" patch first in the corner of the picture to test for fastness.
For a more thorough job, the best method to use in cleaning an oil painting is to use a lanolin based cleaner (such as an unscented or plain hand cleaner) Using a soft cloth or cotton bud, take a little of the cleaner and with a circular motion gently dab the cleaner onto the surface of the painting. Again, check for fastness. To begin with take a small amount on a cotton bud and wipe on; leave for a couple of minutes and then dab gently off.
If the paint does not react with the cleaner, then it will be OK to finish the job. Take your time, as there is no point in trying to rush the process. Too much vigorous scraping at the surface may damage the painting and cause the paint to flake.
Even after the most careful and thorough cleaning, a painting may not regain its original freshness because the protective varnish has yellowed over time. At this point you may decide to speak to a specialist about having your painting restored to its former glory or you may even feel confident enough to have a go at it yourself.
Professional advice is so very important. If your painting is valuable, then personally I would advise you to have it professionally treated. But if the painting doesn't warrant the cost, then it is possible to do the job yourself using a product called conservation liquid, which is a mild solvent.
Conservation liquid is formulated to clean and remove varnish from your painting and is applied using a cotton wool ball to smear the mix over the painting. Some people may be confident enough to carefully remove the painting from the frame first, which will stop the risk of causing any discoloration to the surround of your picture. Remember to do your test patch first to assess the reaction of the solvent to the canvas.
An application of 3 thin coats of natural picture Damar varnish should be applied after the old varnish has been stripped. Each coat of varnish should be allowed to dry for at least four days, with the last coat being applied after an interval of six months.
The cleaning and restoration of old paintings is not a job to be taken lightly. I cannot stress how important it is to do test patches first before you go ahead with your chosen method of treatment. Leave the test patch for at least five to ten minutes before checking the result and only proceed with the process if you are utterly confident in the method being used.
Before beginning the restoration it is always advisable to seek a professional as to the worth of your painting. Be aware of the fact that if you decide to go ahead with restoring a valuable painting, you may have to accept that in bringing the picture back to its former glory, you could be considerably devaluing an irreplaceable work of art.