THIN-SECTION PETROGRAPHY IN STUDIES OF CULTURAL MATERIALS
CHANDRA L. REEDY
3 GLASS AND GLAZES
Glass, as a noncrystalline material, does not normally reveal any useful information in thin section. However, optical microscopy has at times been a useful adjunct to x-ray diffraction and electron microscopy for studying devitrification processes in glass, the development of cracks and crack profiles, and inclusions that reflect the production history, homogeneity, and stability of glass (Porai-Koshits 1973; Simmons et al. 1982). For example, some of the mineral inclusions found in 19th-century glass include wollastonite, diopside, cordierite, and quartz (Barger et al. 1989).
The study in thin section of glazes on ceramics, as in the case of glass, can be used to identify crystalline inclusions. In addition, a thin section can help to determine if any interactions have occurred between the ceramic body and the glaze. As one example, thin sections, in conjunction with other methods of analysis, have been used to study Korean celadons (Newman 1991; Koh Choo 1992). These objects consist of stoneware with a pale green or greenish blue glaze that resembles jade in color and texture. They were produced in Korea from about the late 9th century into the 15th century. The earliest works were modeled on Chinese celadons, but distinctively Korean forms and techniques evolved. A variety of factors contribute to the visual appearance of the glaze. These include the presence in the glaze of bubbles, undissolved raw materials such as quartz grains, and minerals such as anorthite and wollastonite that form during firing of the glaze. Interactions between the glaze and the ceramic body can also contribute to the visual effect, when the body absorbs some of the light transmitted by the glaze and decreases its brightness.