Silas Menlo Scott and Dr. Lawrence Rees, Physics and Astronomy
Particle Induced X-Ray Emission (PIXE) has been used extensively in the study of items of artistic interest. One area of interest has been determining the chemical composition of various artists’ materials.1
Many companies offer a wide variety of artists’ paints. While the chemical makeup of various pigments is standard,2 the actual trace element content of a tube of paint may differ from the trace element content of a tube of the same color paint, but different manufacturer.
Three brands of commercial artists’ paints were selected: Schminke, Winsor Newton, and Grumbacher. Eight colors were also selected: Titanium White, Indian Yellow, Ivory Black, Cadmium Red, Pthalo Blue, Ultramarine, Raw Sienna, and Raw Umber. Each color was selected for at least two of the three brands. All of the selected paints were oil based, having a vehicle of either linseed or safflower oil.
Sample Preparation
A small amount of the paint sample was placed in a 1 mL conical vial and 600 μL of toluene was added. The resulting suspension was mixed using a magnetic spin vane for 24 hours to insure uniformity.
Two targets were prepared for each sample. The target consisted of a thin polycarbonate film stretched across an aluminum frame. 20 μL of the toluene/paint suspension was applied to the polycarbonate film. The toluene was then allowed to evaporate, leaving a thin layer of the paint sample.
To determine the thickness of the paint layer, the targets were weighed before application of the sample suspension and after evaporation of the toluene, giving the total mass of the paint applied to the target. The area of the sample layer was then measured, giving a thickness of the paint layer in mg/cm2 .3
Difficulty was encountered in developing an internal standard for the samples. Several compounds were tested, most notably Palladium chloride. Because artists’ oil paints consist of inorganic material suspended in an organic medium, solubility of both sample (organic) and standard (typically inorganic) proved impractical with the available chemicals.
Due to these difficulties, the decision was made to analyze the ratios of the elements occurring in the sample rather than the exact concentrations. The use of an organo-metallic compound as a standard was discussed, but deemed impractical at this point.
Conclusions
The testing of artists paints is critical to the study of artistic items using PIXE. It gives a fingerprint of each specific paint that can later be used for identification of a work of art. A large database of these fingerprints is necessary for this task.
The procedures used in sample preparation and testing must also be refined so that PIXE can be a more effective tool for the scientific and artistic communities. [4]
Table 1: Samples prepared.
References
- Kusko, B.H., M. Menu, T. Calligaro and J. Salomon. 1990. Particle Induced X-Ray Emission and its Analytical Applications. 288-292.
- Patton, Temple C.. 1973. Pigment Handbook. Volume 1.
- Williams, R.N., R. C. Casellas, N. F. Mangelson, L. B. Rees, L. L. St. Clair, G. B. Schaalje, K.D. Swalberg. 1996. Nucl. Instr. Methods B 109/110, 336-340.
- This research was supported by a grant from the Office of Research and Creative Arts at Brigham Young University. The aid of Dr. Nolan Mangelson, Dr. Larry Rees, Brett Clark and Aaron Ross of Brigham Young University is gratefully acknowledged.