Varnish Recipe

24 Feb 2009

Q: I paint in oil and acrylic, and I've successfully used an acrylic final varnish for both. I seem to have misplaced this final varnish recipe, but I believe that it was part gloss and part matte. Can you recommend a recipe of this type for me?

A: Because new products, including new synthetic varnishes, become available with some frequency, it is best to start with a fresh recipe and to perform a few tests to get the desired results. To formulate a final acrylic varnish with the preferred finish-which is somewhere between matte and gloss and is suitable for use on both oil and acrylic paintings-begin with a mixture of 1⁄2 matte synthetic varnish and 1⁄2 gloss synthetic varnish. Mix a small amount of solution and apply it over two different painted surfaces, one oil and one acrylic. When the test surfaces dry, you will be able to determine whether to add more matte or more gloss, or whether the final varnish is just right. Keep a record of the amounts of each type of varnish used and then write down the final recipe.    

Read the labels on synthetic varnishes carefully to become familiar with the ingredients. For example, a gloss varnish may contain mineral spirits with a ketone resin, while a matte varnish may have those same ingredients, plus some translucent liquid wax. These ingredients are compatible and, when blended together, will produce a satin finish between a gloss and a matte.    

Synthetic varnishes are more permanent than their natural counterparts or those made with damar and mastic; they are also more elastic and do not yellow or become brittle with age. Regarding conservation concerns, synthetic varnishes are reversible with good-quality mineral spirits or turpentine. It is important to mention that although synthetic varnishes can be used to varnish oil paintings, unlike natural resins, they do not combine with oil paints to make painting mediums.

Q: I have been given an oil painting to repair by a friend who has a nostalgic connection to the artist. The painting is about 40 years old and has been stored in a garage with many others, is dirty, and has a dull appearance. It has also been chipped in a number of places, primarily along the stretcher bar, and the chips are rather large in size. When I received the painting, I noticed many cracks along the top as well, which lead me to believe that the painting will crack and chip even more. The painter was untrained and probably did not use professional-grade art materials and also probably used turpentine, both as a thinner and as a medium.

A: Without lamenting the number of paintings that have been harmed by amateur conservators and extolling the virtues of professional conservation, it is still necessary to give fair warning that professional treatment is the only answer. Even so, there are no guarantees the painting can be improved and that treatment will not cause harm to the already damaged work. The following information, then, is only suggestions on how you can care for paintings when professional care is not an option.

First, consider some of the causes for the conditions that you describe. Oil paintings stored in the dark will often turn yellowish, especially the whites, and with moisture added to the equation the situation worsens. It is difficult to gauge the atmosphere of the garage where the painting was stored, but extreme changes in temperature can be just as damaging to the stretcher bars, causing warping and splitting, as to the paint surface itself, which can suffer from the expansion and contraction of the support.

The chipping of the paint along the stretcher bars sounds like flaking, a condition that jeopardizes the integrity of the whole painting. Flaking is usually caused by exposure to extreme atmospheric changes. If that is the case, any attempt at cleaning the painting will only cause more damage to the picture. Proceed with extreme caution, and as soon as any cracking or flaking appears on the surface, suspend further treatment to the painting.  

The dirt, on the other hand, sounds superficial. If it is, use crumbs of soft bread kneaded like a plastic eraser to gently clean off the painting. If there is no change to the surface of the work, you can gently vacuum the reverse side of the canvas. Do not attempt to vacuum the front side of the canvas, however, because the paint chips will be lost. Since the painting is thoroughly dry, you can also rub it gently with a piece of cotton moistened with a tiny amount of turpentine or solvent; but this is only if the bread crumbs do not remove the dirt. Since the materials of the painting are not known for certain, be extremely cautious when using any solvent. Use small cotton swabs for this procedure and change each one as soon as it becomes dirty. Turpentine is a strong solvent and must be managed very carefully.  

Normally, lost areas of paint can be filled in with a reversible mixture of stiff glue gesso that handles like putty. When the holes are filled, they can be retouched, which, in picture restoration, is called in-painting. Usually a reversible paint, one that may be different from the paint used in the original work, is applied. In this case, however, it is advisable to leave the chipped areas of the painting untreated, especially since they are located at the edges of the painting. Based on the description of the painting's condition, the less it is handled, the better.

Last, there is the issue of the painting's surface appearing dull. Varnish provides a protective coat to the surface of an oil painting and unifies an uneven surface. It can also add a soft glow to a dull surface. The varnish should not be too glossy, however, or the picture will be difficult to see; conversely, the varnish should not be too matte, or it will not protect the picture. A semigloss varnish, then, is usually the ideal solution. In this instance a spray-varnish coating is recommended, because it is less invasive than brush-on varnish. It is important to varnish on a dry, sunny day. Remove any dust from the room and keep all the tools free from moisture. Be sure there is proper ventilation in the room because spray varnishing introduces fine particles of resin and solvent into the air. Always wear protective gloves and an organic vapor respirator when varnishing.

by Jane Sutherland


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