The secrets behind ancient red fingerprints

FOR tens of thousands of years, Aboriginal Australian artists have used ochre from the earth, with its rich red, yellow and brown hues, to express their Dreamtime stories.

Now this ancient material is to be chemically ''fingerprinted'' in the first comprehensive high-tech survey of ochre from across the country.

Dr Rachel Popelka-Filcoff, a research associate at Flinders University, says her research will help uncover the sources of the pigment used in different pieces of art, on artefacts such as spears, shields, paddles and boomerangs, and from archaeological contexts such as burials as well as rock art.
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It could also reveal how the precious substance was traded between groups of Aborigines as they moved about the continent.

''It could shed light on cultural interactions between groups that have been lost to history,'' she says.

People often travelled long distances to places where special ochre could be found. A site in the Flinders Ranges in South Australia, for example, was an important place for coming-of-age ceremonies for young men.

The ochre there is a dark, purple red, and was used to decorate the skin as well as for art, says Popelka-Filcoff. ''It has a very sparkly quality to it because of its crystalline structure.''

People travelled hundreds of kilometres to participate in the ceremonies and to mine the ochre, she says. ''And they would carry up to 35 kilograms of it on their heads back home to their original communities.''

As a first step in the project, Popelka-Filcoff and her colleagues are using the OPAL nuclear reactor at the Australian Nuclear Science and Technology Organisation's Lucas Heights facility to analyse 100 samples from four main ochre sites, in South Australia, the Northern Territory and Western Australia.

''These are the sites that have the greatest amount of ethnographic and historical information about how the ochre was mined and used,'' she says.

Lucas Heights is the only facility in Australia able to provide neutron activation analysis, which can detect more than 50 elements in a sample.

While elements such as iron, calcium, potassium, aluminium and others are present in large amounts in ochre, the method can also identify elements that are there in trace amounts of only a few parts per million, such as lanthanum, europium and other rare earth elements, and antimony.

The iron oxide pigment is first irradiated with neutrons from the OPAL reactor and then the energy of the gamma rays it emits as the sample decays is used to determine the elements present and their concentrations.

Ochre samples from different areas have different chemical signatures, reflecting the original geology of the source site, says Popelka-Filcoff, who has used the technique in the US to distinguish between ochres from different areas of North America and Peru. ''We can look at it as a fingerprint or a signature.''

The samples from the four main Australian sites were collected between five and 100 years ago, and were received from the South Australian Museum and other collaborators, she says.

Eventually an online database will be built with the chemical signature of ochre from as many sites as possible. It will be a valuable resource for those wanting to study Aboriginal history, art and culture, says Popelka-Filcoff, whose research is part of a project with the South Australian Museum and Artlab Australia.

Ochre has great significance in Aboriginal culture. Its colour evokes connotations of death and blood, and its application to something like a spear was able to transform the cultural meaning of the object.

Eventually it will be possible to test ochre samples from objects in the museum and elsewhere using the nuclear technique and compare their fingerprints with the database to try and identify their origins and understand ancient exchange routes.
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References:

Smith, Deborah. 2010. "The secrets behind ancient red fingerprints". Sydney Morning Herald. Posted: September 9, 2010. Available online: http://www.smh.com.au/national/the-secrets-behind-ancient-red-fingerprints-20100908-151d5.html