Jia-sun Tsang

SOME IMPROVEMENTS IN THE STUDY OF CROSS SECTIONS

AbstractThis paper outlines techniques developed at the Conservation Analytical Laboratory. Smithsonian Institution, for the preparation of thick cross sections (50 microns and up) and microtomed cross sections (10 microns and up) of small samples from works of art. The sectioning methods discussed here enable us to maximize the information that can be retrieved from samples of paint films. One advantage of the 10-micron microtomed sections is that they are thin enough to be analyzed non-destructively using transmission Fourier transform infrared spectrometry (FTIR). These results can be used as the first material classification step in our analytical materials identification scheme. We can then proceed using destructive chemical and physical tests of thin-sections with greater confidence. The identification of the binding media and pigments from several cross sections is also described.

Degradation of ‘Lumarith’ Cellulose Acetate

Abstract Objects manufactured from cellulose acetate comprise one of the most problematic groups of plastic in the collections of the Smithsonian Institutions National Museum of American History (NMAH). To understand better cellulose acetate degradation, a ‘salesmans sample kit’ of ‘Lumarith’ brand, injection-molded, cellulose acetate color samples, manufactured by the Celluloid Company in the early twentieth century and now in the NMAH collection, was studied using minimally invasive analytical techniques at the Smithsonian Institutions Museum Conservation Institute (MCI). The kit includes 49 plastic coupons that vary in color, transparency, chemical composition and current state of degradation. Results of analysis were compared with Celluloid Company records at the NMAH Archives Center and Celanese Corporation in Narrows, Virginia, in order to determine the causes for their current level of preservation or degradation. The possible reasons for the degradation of some coupons are discussed; methods are proposed for identifying cellulose acetate objects that are at risk and for early detection of degradation.