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
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.