4.3 Microspectroscopy of Dyes, Pigments, and Varnishes
 

University of California, Los Angeles
The Getty Conservation Institute

Jeff Zink
Londa Larson
Debbie Preston
Gary Hollingsworth
Michele Derrick
Frank Preusser
Period of Activity: 7/86 to 7/87

Project Abstract
The objective, which was achieved, was to develop a reliable nondestructive method for identifying microsamples of dyes, pigments, and natural polymers. Using laser excited luminescence spectroscopy (including both fluorescence and phosphorescence spectroscopy).

Major Findings and Recommendations
The technique of microluminescence spectroscopy works for a wide range of pure synthetic and natural polymers as well as pigmented systems; however, the reliability and reproducibility of the spectral characterization needs to be demonstrated with single polymers or polymer/pigment combinations having undergone different processing steps. It is not clear what changes, if any, cast films will show from materials supplied by the manufacturer or the role of different solvents in potentially extracting fluorescent components. Three areas of future work should include: (1) a closer examination of the spatial inhomogeneities found in samples taken from works of art, (2) wavelength dependencies and temperature effects, and (3) the lifetimes of luminescences.

Primary Publications
Larson, L. J., K-S. Shin, and J. I. Zink, "Photoluminescence Spectroscopy of Natural Resins and Organic Binding Media of Paintings," Journal of the American Institute for Conservation, Vol. 30, 1991, pp. 89-104.

ABSTRACT-The photoluminescence spectra of a variety of natural resins and organic binding media used on paintings are reported. A few mixtures of these materials with one another and with pigments were also studied. The application of this technique toward the identification of these materials is considered. Both bulk materials and films prepared from selected bulk materials were studied, and a comparison is made between the bulk and film samples. Temperature and excitation wavelength studies are reported and discussed for several of the samples.

Larson, L. J., K-S. Shin, and J. I. Zink, "Laser Spectroscopy of Materials Used in Paintings," Materials Issues in Art and Archaeology II, Vol. 185, 1991, Proceedings of the Materials Research Society Spring Meeting, San Francisco, California, April 16-21, 1990, pp. 133-138.

ABSTRACT-A wide variety of natural resins, waxes, gums, drying oils, and proteinaceous materials used on paintings are photoluminescent. The photoluminescence spectra of microsamples of these materials are reported and discussed. The application of this technique toward the identification of these materials is considered. Both bulk materials and films prepared from selected bulk materials were studied and a comparison is made between the bulk and film samples. Temperature and excitation wavelength studies are reported and discussed for several of the samples.

Secondary Publications
Larson, L. J., and J. I. Zink, "Luminescence of Alizarin and its Metal Complexes," Materials Issues in Art and Archaeology II, Vol. 185, 1991, Procedings of the Materials Research Society Spring Meeting, San Francisco, California, April 16-20, 1990, pp. 139-144.

ABSTRACT-The red/near infrared emission spectra of alizarin (1,2-dihydroxyanthraquinone), the potassium salt of alizarin, and the aluminum and zinc complexes of alizarin in the solid state are reported. The emission is assigned to an alizarin localized transition from an in-plane nonbonding orbital delocalized over the anthraquinone nucleus to a predominantly pi* quinone C=O acceptor orbital (npi* ligand localized excited state). The cobalt, nickel, and copper complexes do not emit from their npi* state. In these complexes, metal centered d-d excited states which lie lower in energy than the ligand localized npi* state effectively deactivate the luminescence.

Larson, L. J., K-S. Shin, and J. I. Zink, "Photoluminescence Spectroscopy of Natural Resins and Organic Binding Media of Paintings," Journal of the American Institute for Conservation, Vol. 30, 1991, pp. 89-104.

ABSTRACT-The purpose of this study is to test the feasibility of applying microluminescence techniques to the identification of actual painting materials. Specifically, a large number of authentic and previously characterized samples of natural resins and organic binding media used on paintings are surveyed. Interestingly, all of the samples which were surveyed used luminescence, which suggests that the technique will be useful. A continuous wave tunable argon ion laser served as the excitation source thus allowing flexibility in the excitation wavelength. By employing a laser as the excitation source, samples or portions of samples as small as approximately 100 Ám in diameter were nondestructively analyzed in this study.