Traditional Oil Paints: The Effects of Long-Term Chemical and Mechanical Properties on Restoration Efforts
- PDF / 125,936 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 28 Downloads / 160 Views
Traditional Oil Paints: The Effects of Long-Term Chemical and Mechanical Properties on Restoration Efforts
Marion F. Mecklenburg and Charles S.Tumosa Introduction Some of the most important cultural icons in the world are oil paintings. Preserving them for future generations requires a fundamental understanding of the longterm chemical, mechanical, and physical behavior of their components. If the properties are understood, modeling and even predicting the effects of exposure to changes in temperature, relative humidity, shock, and vibration are possible.1,2 Furthermore, if the chemistry and rate of the drying of oil paints is understood, predicting the effects of both structural and cosmetic (cleaning) conservation treatments is possible. In the late 1980s, the Smithsonian Center for Materials Research and Education (SCMRE), formerly the Conservation Analytical Laboratory (CAL), purchased custom-manufactured oil paints for a research program examining several aspects of oil paint behavior. Thirty-nine different pigments and six different oils were used in mixing the paints. No other fillers, extenders, or driers were added to the paints, which is in marked contrast to commercial artists’ oil paints currently manufactured. This restriction was imposed so that the custom-made paints would more closely resemble those used in past centuries. The only consideration was the interaction of pigment and oil. Two of the most pressing questions were how do pigments affect the drying of oil paints, and how long does it take for paint to dry? The latter
MRS BULLETIN/JANUARY 2001
question held the most interest, in that some conservation research has been done on modern paints up to 10 or so years old in the hope of developing a better understanding of the conservation treatment of paintings and painted surfaces that are hundreds of years old.3–6 The principal criticism of these experiments was that the paint samples used by these researchers were not old enough to truly represent old paint films. This paint research program was undertaken to study the effects of pigments on the behavior of oils and to determine when the chemical and physical processes of drying reached equilibrium. The determination of the time frame for chemical (oxidation) and physical (mechanical) processes is reported here.
Sample Preparation and Testing The paints were prepared for drying by uniformly applying them to clear polyester sheets so that, after a period of time, “dry” paint films could be cut and the polyester film backing peeled away. The thickness of a typical paint sample was 0.25 mm. In this way, an unsupported paint sample was capable of being tested for chemical, physical, and mechanical properties. Several hundred paint samples were prepared and tested over the past 10 years. Specimens were weighed periodically with a Mettler balance to 0.1 mg. Tensile tests were performed on miniature
screw-driven tensile testers. The average strain rate was a very slow 0.0005 mm/mm per second, to minimize time-dependent behavior. Temperature and r
Data Loading...
