In Thai temples Buddha images of varying dimensions may be installed in the image-shrine hall (wihan) for public worship, in the abbot’s residence, or concealed from view altogether as deposits inside stupas (chedi). The present group of thirteen heads of the Buddha could have served any of these three functions. The separation from their figures, however, suggests that they may have been ritually deposited and suffered destructive corrosion. Certainly some display the patinas indicative of buried objects. The heads group into two stylistic types. The first, best demonstrated by 1975.1.1438 belongs to the older tradition associated with the Sukhothai of northern central Thailand. This style was defined in the mid-fourteenth century and persisted until Sukhothai was annexed in 1438 by the rival kingdom of Ayutthaya. The Sukhothai style is characterized by a stylized face with extended conical (“stupa-like”) or flame projection (ushnisha) from the skull. This manner became embedded in the national tradition and persists into recent times. See 1975.1.1429 – 1431; 1975.1.1433 – 1438. The second group is in the Ayutthaya style (1975.1.1432; 1975.1.1439 – 1441). The pieces are readily distinguished from the Sukhothai school by the use of a distinctive diadem, typically with lozenge and crosshatched design and by the multitiered conical skull projection. The raised, modeled eyebrows, merging at the bridge of the nose, is a feature from the late Ayutthaya period onward. This form is shared by both groups and suggests that they each represent two stylistic streams of late production, and both may be assigned to the later eighteenth to nineteenth century.
Catalogue entry from John Guy. The Robert Collection. Decorative Arts, Volume XV. Wolfram Koeppe, et al. The Metropolitan Museum of Art in association with Princeton University Press, 2012, pp. 367-368.