Restoring paintings with care

We are all caretakers in our desire to pass on to posterity a pictorial record of the past. It is important for anyone who cares about pictures to have a clear understanding of the basic processes of restoration, to be sure that the paintings he or she owns are treated with care and respect.

Perhaps the most important attribute a restorer needs is an attitude toward his work that reflects this sense of responsibility. He must be perpetually cautious.

In the 19th and early 20th centuries, restoration of paintings was performed with abandon. Many canvases suffered from ''overcleaning,'' during which damage was done to the original paint layer.

Only consistent experience in cleaning oil paintings under careful supervision can give the restorer a sense of touch and certainty that he is removing only the layers of varnish and dirt that he wishes to remove, not the original paint.

A typical oil painting has six layers: first, the linen or cotton support or canvas; second, the glue sizing that fixes the canvas to its desired size and shape; third, the supporting layers of ground (the toned surface on which the artist paints); fourth, the actual paint layer; and, fifth and sixth, layers of varnish and dirt films accumulated with time.

Damage can occur to any or all of these layers from trauma or atmospheric effects, such as extremes of heat or humidity. The structure, no matter how well prepared by the artist, may show the effects of age. The varnish may brown and obscure the paint layers. The ground and sizing may dry out and prove inadequate to bind the paint to the canvas, and the paint may flake and loosen from its support. The canvas itself may deteriorate and become weak and brittle.

First, the restorer will examine the painting and evaluate its condition, determining what prior work may have been done, and whether or not the painting has suffered damage, such as tears or flaking and lost paint. He will, with the aid of magnification and ultraviolet light, describe the painting's state of preservation in terms of what is original and what has been added or changed later.

If the painting requires lining, this precedes the cleaning. The lining process, or replacement of the linen support, is required when the support layers of the ground and sizing no longer bind the paint layer firmly to the canvas, and when the paint shows evidence of lifting or flaking from the surface.

If the structure of the painting in question is sound, or after the work has been relined, the restorer starts the cleaning process. The dirt film is first removed with a mild solvent. Then the varnish layer is tested for indications of the vulnerability of the paint below it to ascertain what strength of solvent should be used.

After cleaning, areas needing retouching become more clearly accessible. These are filled with a spackle-like compound and sealed with a layer of shellac , always keeping the fill confined to the sometimes minute areas of actual loss. Then the picture is ready for retouching.

In recent years there have been changes in approach and attitude regarding retouching or in-painting. In the past it was common to cover whole areas of a damaged painting with overpaint without regard for obscuring the original picture. This was no doubt more enjoyable and easier than meticulously attempting to match colors to the original and keeping work confined to filled areas and areas of lost paint. Today, the whole purpose of restoration is to maintain the original without alterations.

There are various techniques in retouching, some of which have evolved in an effort to confront the problem of darkening and color change that is inevitable as the oil paint dries. Varnish is often used as the medium in retouching because it can be easily removed to reveal the original state of the painting when cleaned. Although varnish is apt to yellow and change the color of the paint in the touched-in area, it is still the most satisfying and adaptable method to some restorers. It is also becoming common for retouchers to use tempera paints for in-painting. These are water-based and somewhat less fugitive in terms of color.

Finally, the process of resurfacing the painting completes the restoration. This is accomplished with synthetic varnishes that do not yellow and are easily removed. Usually a combination of matte and glossy finishes is required to arrive at a surface that protects the painting without obscuring it.

The owner of art work should become adequately informed about the care and treatment of his collection (or even his family portrait) before presenting a picture to a restorer for repairs. Consultation with local museums and historical societies, or with conservators and restorers, is directly available to most people and is an invaluable guide.