4.4 The Use of Infrared Microscopy in the Analysis of Cultural Artifacts

Loyola Marymount University
The Getty Conservation Institute

James M. Landry
Steven P. Bouffard
Margaret R. Bolton
Michele R. Derrick
Dusan Stulik
Period of Activity: 4/89 to 4/90

Project Abstract
This research project investigated the use of infrared microspectroscopy as a tool in analytical problems associated with cultural artifacts. The research examines methods of analysis and defines limitations of the technique with respect to three specific areas of interest:

a.) Binding media
b.) Organic colorants
c.) Layered coatings and dyes in fibers

Primary Publications
Derrick, M. R., D. C. Stulik, J. M. Landry, and M. R. Bolton, "Infrared Microspectroscopic Identification of Binding Media in Paint Cross-Sections: Application to Works of Art," Paper presented at the 1990 Pittsburgh Conference, New York, New York, March 5-9.

ABSTRACT-Modern methods of chemical analysis are able to reveal many details about techniques used by artists and craftsmen in the creation of works of art. One of the most difficult questions addressed to an analytical chemist by a restorer or art conservator is a problem of identification of binding media in paintings and polychrome structures. We wish to report work involving the identification of binding media and stratigraphy of paint cross-sections using infrared microspectroscopy.

Microscopic paint cross-section samples from paintings were cut using a sharp tip of a microscalpel. Samples were embedded in an appropriate embedding medium and 10-20 mm sections were sliced using a microtome. Cross-sections were placed on a BaF2 window on a mapping stage of an infrared microscope. Infrared spectra were collected in 20 mm steps across the layered structures.

The spectra obtained were compared with a previously generated infrared spectral library of binding media which were historically used by painters and colorists. This allowed routine identification of binding media in the ground and paint layers along with the components in protective varnish layers. The details of the analytical methodology are documented on case studies of medieval, nineteenth-century, and modern paintings.

Landry, J. M., S. P. Bouffard, M. R. Derrick, and D. C. Stulik, "Infrared Mapping Microspectroscopy of Furniture Finish Stratigraphy," Paper presented at the 1990 Pittsburgh Conference, New York, New York, March 5-9.

ABSTRACT-A knowledge of the stratigraphy of varnish and lacquer layers in surface finishes on antique furniture is important not only for authentification but also for development of proper treatment and restoration strategies. This paper describes the use of infrared mapping microanalysis of furniture finish cross-sections to identify individual varnish layers and to determine their sequence of deposition.

This study employed the five resins most often used in historical furniture finishes: shellac, sandarac, mastic, copal, and rosin. Multilayer samples were prepared by applying several coats of resin solutions to mahogany wood, Teflon or polyethylene surfaces. Cross-sections suitable for infrared analysis were prepared using one of two methods. One approach involved microtoming cross-sections directly from a portion of the multilayer sample attached to the mahogany surface. In the other approach, a portion of the finished sample on the Teflon or polyethylene substrate was removed and embedded in an appropriate embedding material. For both methods, the cross-sections were microtomed to 10-20 mm sections and placed on BaF2 windows on a mapping stage of an infrared microscope. Linear maps of the cross-sections were generated using 20 mm steps across the layered structures.

The infrared spectra from the linear maps of the prepared multilayered samples resulted in identification of the appropriate resin layers. The typical resin layer was found to be 50-100 mm in depth and therefore easily analyzed by this technique. In cases where visual distinction of the layers was possible, the results from both optical and infrared microscopic analysis were consistent. This technique was used for analysis of samples from eighteenth- and nineteenth-century European and American furniture. eighteenth- and nineteenth-century European and American furniture.

Derrick, M. R., D. C. Stulik, J. M. Landry, and S. P. Bouffard, "Infrared Mapping Microspectroscopy for Identification of Furniture Finish Layers," Paper presented to AIC-WAG Specialty Group, American Institute for Conservation Annual Meeting, Richmond, Virginia, 1990.

ABSTRACT-The use of infrared microspectroscopy to identify individual varnish layers in furniture finishes is described and discussed. Facsimiles of multilayered furniture finishes were prepared on a mahogany substrate using combinations of five natural resins: shellac, sandarac, mastic, copal, and rosin. After drying, cross-sections of the samples were removed, embedded in an appropriate medium, and microtomed to give a transparent thin section for analysis. The sample was then placed in an infrared microscope and spectra were obtained in 20 mm step increments across the varnish layers. Using this technique the identification of individual resins in multilayer varnish structures is possible. It was also found that the sharpness of the boundary between finish layers is a function of both the resin concentration in solution and the drying time before deposition of another layer. Application of this newly developed analytical methodology is documented on real sample cross-sections of varnish from eighteenth- and nineteenth-century furniture.

Derrick, M. R., D. C. Stulik, J. M. Landry, and S. P. Bouffard, "Furniture Finish Layer Identification by Infrared Linear Mapping Microspectroscopy," Journal of the American Institute for Conservation, Vol. 31, Nš 2, 1992, pp. 225-236.

ABSTRACT-None available.

Derrick, M.R., "Infrared Microspectroscopy Mapping Techniques for the Analysis of Cross Sections and as a Non-Destructive Analysis Method for Paint on a Manuscript", Materials Issues in Art and Archaeology IV, Vol. 352, 1995, Symposium held May 16-21, 1994, Cancun, Mexico, Materials Research Society, Pittsburgh, Pennsylvania, pp. 97-103.

ABSTRACT - Infrared microspectroscopy is useful for characterizing media in very small cross section samples using both transmission and reflection modes of analysis. In a direct comparison of the two methods, reflection techniques produce poorer quality spectra than the transmission methods. However, many of the problems of reflectance spectra can be mitigated by looking at variations that occur between spectra obtained under similar conditions. An excellent venue for such a study is the use of infrared mapping. Mapping studies compare the intensities of absorption bands versus their location in the sample to generate an image of compositional differences in a region. Several examples are shown in his paper for the application of infrared mapping to the determination of components in thin section and cross section samples. The technique for infrared mapping was also used as a direct, non-destructive method for the characterization of colorants and binders on a small painted manuscript leaf. Compared to the paint cross sections, four relatively large areas (1 cm2) were mapped with the infrared microscope then joined together using a mosaic technique.