Note. This is the first in a series of six pages about common painting problems. Use the menu at left to select other subjects of interest. If you wish to see a larger rendition of any photo, just click on it.

Dirt. Over the years, paintings accumulate all sorts of environmental insults, including airborne dust, grime, soot and tobacco smoke; flyspecks; spattered and rubbed liquids (beverages of all kinds, cleaning agents, wall paint, etc.); mold and mildew; and many other materials. These materials are not only unattractive, but can do permanent damage to unprotected artworks. That's why delicate paint films are traditionally protected with transparent glazing materials (glass, Plexiglas, etc.) and/or varnish. During the modern era, however, it has become common for artists to not only eschew these protective measures, but also to use techniques and materials which leave the completed artwork exceptionally vulnerable to environmental hazards. Conservation treatment often includes removal (or partial removal) of dirt and other unwelcome materials.

Yellowing varnish. Varnish is applied to paintings for two main reasons — to give the image more visual "punch" by saturating the colors, and to protect the delicate painted surface from mechanical damage and other environmental hazards, such as airborne grime and spattered liquids. At its most basic, a varnish consists of a resin dissolved in a volatile liquid. After the mixture is applied to a painting, the solvent evaporates, leaving a film of resin on the surface of the paint. All varnishes made from natural resins (such as damar or mastic) tend to yellow as they age, and many synthetic varnishes also discolor with time. Discolored varnish is not necessarily harmful to an artwork, but can detract considerably from its visual appeal. Conservation treatment often includes removal of old, discolored varnish, followed by application of a new varnish coating.

About the photos. Of the paintings pictured at right, the upper two are traditional oil-on-canvas. They were photographed during cleaning. At some point in the past, the portrait got quite dirty and was not cleaned before being varnished. The ship, by contrast, was clean when it was varnished, but later accumulated a substantial layer of dirt on top of the varnish. In the case of the colorfield painting, high relative humidity caused massive mold growth in a very short time.

Portrait during cleaning: removing varnish over dirt. Ship painting during cleaning: removing dirt over varnish Brown mold stains on colorfield painting