Why Might My Painting Need to be Cleaned?

Taking care of your paintings is delicate and complex.  As paintings age, the appearance of the image changes not only because of accumulated dirt, but also because aging itself can alter the materials that make up the image.  Methods of removing dirt and other obscuring material requires great skill because any changes to the painting surface may bring about irreversible and damaging results, permanently affecting the aesthetic and monetary value of the work.

What Is Cleaning?

Discolored varnish can be removed during the cleaning of the painting surface.  Cleaning is an irreversible treatment and one of the most demanding areas of painting conservation.  Cleaning requires the skills of paintings conservators who have years of formal training and practical experience.  Permanent damage may easily result from even the most cautious attempts to clean a painting by an untrained person.   Cleaning and varnish removal are skills that require a thorough understanding of art, art history, chemistry, and materials science.  It demands and understanding of the materials included in each layer of a painting's structure.  Improper cleaning can cause a painting to lose its aesthetic and monetary value.

How Complicated is the Cleaning of Paintings?

The technology and technique of cleaning are constantly being improved upon.  Caution is advised when searching the literature for cleaning instructions.   Textbooks, even up to the late nineteenth century, contain recipes for removing tough varnish layers which will also remove some of the paint layer.

The interaction of water and solvents with the many components of a painting must be understood and taken into account.  Often, damage from improper cleaning may not be immediately apparent.  For example, improper cleaning may weaken the adhesion of the ground layer to the support resulting in flaking paint, either immediately or at a later time.  Excess water used in cleaning may change the dimension of the fabric layer due to swelling and shrinking of the fibers.  This fiber movement can put unnecessary tension on the paint above, and cause it to flake off.   Water might wash out some water-sensitive additives in acrylic paint and colorants.   In addition, mild organic solvents can soften acrylic paints.

Preliminary tests carried out by a conservator can determine the solubilities of the varnish and original paint.  Sometimes, grime or discolored patches on top of the varnish can be safely removed by water-based or weak organic solvents without removing the varnish.  Permissible cleaning agents are determined by the character and solubility of surface accretions, however, the character and solubility of the paint layer that they rest against must always be concurrently considered.

Cleaning is seldom a simple matter.  Ultra-violet light has been used to reveal the presence or absence of a continuous varnish layer, of overpainting or inpainting, or of surface accretions.  Aged natural resins have a yellow green fluorescence which may be used to distinguish them from new coatings.  However, ultraviolet light cannot penetrate a thick varnish to reveal existing features such as overpaint.  Sometimes, it it difficult to tell the old overpaint from the original paint.

Is it Possible That My Painting cannot be Cleaned?

Repaint over previous damages may have been executed in a media far tougher than the original paint.  When a less-soluble repaint lies directly on top of an original, more-readily-soluble layer, the only way to remove it is by mechanical means under magnification, and even then not without some minute losses.  Do not attempt to remove even a minor blemish from a painting.  Any disruption of the surface resulting from inexpert attempts to clean may cause an even more unsightly spot, which may result in permanent damage to the painting.

Some paintings simply cannot be cannot be cleaned.  There are paintings that have an image layer so sensitive that no known agent can be effective in removing the films which obscures it without causing extensive damage.  When there is any doubt as to the survival of a design layer, conservators will often choose to leave it dirty and discolored.  It is always wiser to accept the underclass than the overclean.   Technological developments may provide a more appropriate cleaning method in the future.

Selected Bibliography

Carr, Damson W. and Leonard, Mark, Looking at Paintings: a Guide to Technical Terms, Malibu, CA: The John Paul Get Museum, 1992.
Gets, Rutherford J. and Stout, George L., Paintings Materials, New York, NY: Dover Publications, 1966.
Gottsegen, Mark David, The Painter's Handbook, New York, NY: Watson-Guptill Publications, 1993.
Keck, Caroline K., A Handbook on the Care of Paintings, The American Association for State and Local History, 1965.
Keck, Caroline K., How to Take Care of Your Pictures, The Museum of Modern Art and The Brooklyn Museum, 1954.
Stout, George L., The Care of Pictures, New York, NY: Columbia University Press, 1948.
Thomson, Garry, The Museum Environment, 2nd edition, Boston, MA: Butterworths, 1986.