Though this figural urn is now in one piece, it was reassembled from many fragments before arriving at the Walters. Missing parts were re-created using modern restoration materials, shown in green in the photograph. The light brown color of the surface is not dirt but modern paint used to disguise the repairs. It is important that we identify modern repairs, because they can alter the object’s appearance. As we choose areas to sample for thermoluminescence dating, we need to make sure we are testing the original object. Four areas of this urn were sampled for thermoluminescence dating; all indicate it was fired 1,200 to 1,900 years ago, falling within the proposed date range of manufacture (450–650 CE).
How can you date ceramics? The object themselves give us the answer. The three Zapotec sculptures, Pitao Cozobi (Maize God) Impersonator Urn and the Cociyo (Rain God) Effigy Urns, were made of clay, which when fired, turned into ceramic. Small samples were taken from both urns and sent to Oxford University in England for thermoluminescence (TL) dating. The principle behind TL analysis is that specific minerals within clay absorb energy at a predictable rate. When the clay is fired, the minerals release all their energy. This sets the “TL clock” back to zero, and then once again the clay minerals begin to absorb energy. When we tested samples from these urns, the absorbed TL energy was released and measured. This told us how long it had been since the urns were last fired. The TL data show that the urns were, in fact, created between 1,200 and 1,900 years ago.
- Exploring Art of the Ancient Americas: The John Bourne Collection Gift. The Walters Art Museum, Baltimore; Frist Center for the Visual Arts, Nashville. 2012-2013.
- Excursions through the Collection: Portraiture, Adornment, and the Natural World. 2019-2020.