AN INVESTIGATION OF THE REMOVABILITY OF NATURALLY AGED SYNTHETIC PICTURE VARNISHES
SUZANNE QUILLEN LOMAX, & SARAH L. FISHER
5 RESULTS—POLY(N-BUTYL METHACRYLATE)
TWO DIFFERENT types of paintings were examined in this study. One group consists of “old master” paintings to which coatings of Elvacite 2044 were applied in the 1970s and which have been on continuous exhibit under Plexiglas UF3 filtered daylight. The other group contains early American naive paintings to which the coatings were applied in the 1950s. Although these American paintings have been primarily in storage, many have been exposed to light in occasional loan exhibitions. The unpredictable solvent sensitivity of the paint layers on these paintings made them of special concern with regard to varnish removability.
Thirty-one paintings with poly(n-butyl methacrylate) coatings were examined: 9 “old masters” and 22 early American paintings. On the “old master” paintings, a soft and rubbery gel formation occurred immediately either with cyclohexane or a mixture of cyclohexane and toluene. More varnish was removed with toluene. On three of the paintings, toluene alone was sufficient to remove all of the poly(n-butyl methacrylate). On two paintings, the poly(n-butyl methacrylate) had been applied over a coat of B-67, which is poly(isobutyl methacrylate); toluene-acetone mixtures (60:40) removed this lower layer. On the remaining paintings, removal of poly(n-butyl methacrylate) continued and was only completed when acetone was applied.
On almost all of the 22 early American paintings, a mixture of 60% cyclohexane, 40% toluene, applied by swab, began to remove the varnish. Usually a soft, rubbery gel formed. More varnish was removed with toluene, and, in most cases, the varnish was completely removed in 60% toluene, 40% acetone. The poly(n-butyl methacrylate) was always found over a layer of another varnish, usually a natural resin, and this lower layer could usually be removed with acetone. However, on two of these early American paintings, pigments began to be removed with the acetone-toluene mixture or with pure acetone. These pigments were all in dark areas.
Before considering this group of paintings as representative of poly(n-butyl methacrylate) behavior in time, an important fact must be considered: The paintings consist either of cases where the coatings were recently applied and the paintings have been on exhibition, or the coatings were applied 35 to 40 years ago and the paintings have been kept in storage. The individual paintings were chosen for the simplicity of the coating stratification. Since the amount of light is an important factor in the degradation of coatings, paintings with a greater amount of light exposure should be tested, even though the varnish stratification might be more complex.