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News Release:

Ancient prank sets up space-age experiment

Date 20/8/03 No 126/03

A child's prank in Roman Pompeii has set the scene for a unique 21st-century experiment on the dating of plaster in ancient buildings.

Almost two thousand years ago a wall of a newly plastered and painted room in one of Pompeii's grand houses was peppered with coin impressions before the plaster had set.

Dr Peter Grave, an archaeologist at the University of New England, thinks one likely explanation is that a child walked through the room in the House of the Ancient Hunt, repeatedly pressing a coin into the wet surface. (The impressions are on the lower part of the wall.)

Dr Grave, an expert in the analysis of ancient mortar and plaster, said the impressions were still legible enough to identify the coin that made them as a sestercis of the Emperor Vespasian, with a date of either 59 or 61 AD. "As the disastrous eruption of Vesuvius occurred in 79 AD, the impressions must have been made within a period of only 20 years," he said. "This provides us with the most accurate dating of any plaster work that has survived from the ancient world. The dating is unique in that it relies on direct evidence impressed into the plaster surface at the time of its creation."

He intends to use this absolute dating to check (and, he believes, to refute) recent claims in a popular science journal that ancient plaster can be "carbon dated". "Carbon dating relies on the death of an organism," he said. "It detects the transition from life (when there is a continuous interchange of carbon molecules with the environment) to death (when there is no such interchange). In contrast, the lime in plaster and mortar continues to react with the environment throughout its existence. It's continually absorbing carbon dioxide and radio carbon (C14), resulting in the continued growth of calcite crystals within the plaster matrix.


"In fact, because of this process ancient plaster is far harder today than it would have been in antiquity." For these reasons he expects any attempt at carbon dating samples from the wall plaster in the House of the Ancient Hunt to produce erratic results that correspond in no way with the date provided by the coin impressions.

To support this research Dr Grave is applying for a grant from the Australian Institute of Nuclear Science and Technology to have plaster samples "carbon dated" by the Australian Nuclear Science and technology Organisation in Sydney, using a newly-installed accelerator in which UNE is a major stakeholder. The samples will come from plasters he sampled during earlier research at Pompeii while undertaking his Master's degree. This involved an analysis of the plaster in the House of the Ancient Hunt.

Dr Grave was part of a joint German-Australian project that carried out an exhaustive archaeological survey of Pompeian houses first excavated in the 19th century, and was a major contributor to the report on the survey published last year by the German Archaeological Institute. "This is just one example of important collaborative work being undertaken by Australian researchers all round the world," he said. "National Science Week is an appropriate time to be drawing attention to such work."

Media contact: Dr Peter Grave, School of Human and Environmental Studies, UNE, on (02) 6773 2062 or 0400 498 350, or Jim Scanlan, Public Relations, UNE on (02) 6773 3049.

A photograph of Dr Peter Grave is available for download.

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