SOME IMPROVEMENTS IN THE STUDY OF CROSS SECTIONS
JIA-SUN TSANG, & ROLAND H. CUNNINGHAM
IN THE field of conservation we frequently encounter results that are inconclusive due to the sample size and inability to repeat tests because of the destructive nature of the test itself. By using thick-sectioning and microtome-sectioning technique, we increase the number of available tests samples that can be provided from one small original sample. As demonstrated above, there is no single test that can offer the necessary satisfactory results. To confirm one analysis, a number of different tests must be conducted. Even when sophisticated instrumentation such as gas chromatography and high-performance liquid chromatography is used, it is often difficult to relate these results to the complex visual phenomena presented in the cross sections from a painting or artifact. The physical information generated either by the artist or by deterioration must be gathered by methods other than those described. By using microchemical and physical tests on the cross sections, we can correlate the complex visual phenomena presented by a painting with the material composing it. At times, some of the more simple tests (such as the microscopic methods mentioned previously) will generate enough information for treatment purposes. Some of these uncomplicated tests also can provide an opportunity for a quick on-site diagnosis and treatment decision. The advantage of combining tests that can be accomplished using a microscope with chemical and physical analyses should not be ignored by practicing conservators. Our methods of sectioning a small paint sample can provide the conservator with an opportunity to have the confirmatory tests conducted at a later date. The conservator can perform some of the tests to facilitate the ongoing treatments and yet still have samples for research and confirmation.
Few publications are available in the conservation literature on the microtome technique (Papillon et al. 1988; Gay 1970).3 We were able to produce thick sections in addition to the microtomed section. This ability is especially useful in the field of painting conservation because of the unique layered structure of paintings. Chemically separating or physically peeling layers apart can be difficult, provide incomplete results, and is generally impractical.
One of the benefits of the microtomed cross section is that it can be used for FTIR microscope analysis. FTIR microspectrometry has been used in other disciplines to study such materials as plastic laminates in modern photographic materials and ordinary trash bags. Analysis and quality control of these laminates dictate that the correct layers be seen in the proper sequence. IR spectral analysis of each layer becomes easy with the IR-Plan microscope interfaced with an FTIR spectrometer. Each layer's infrared spectrum is recorded after it is optically isolated in the microscope. The use of the FTIR microscope reduces an intractable analytical separation problem to a simple, direct examination—essentially in a one-step operation.