DELICATE biological specimens that have been gathering dust in museums for decades could soon receive a spruce up. A laser-cleaning technique more commonly used to clean works of art has produced impressive results when applied to even the most fragile specimens.
Many of the items, such as butterfly wings and paper wasps鈥� nests, are so delicate they are impossible to clean using conventional techniques, says Lorraine Cornish, an expert in artefact conservation at the Natural History Museum in London. She has been testing a laser-cleaning device that is currently used on sculptures and paintings, on biological specimens such as ivory, bone and microscopic fossils (New Scientist, 28 September 2002, p 22). 鈥淲e think it is a very promising mechanism,鈥� she says.
The device works by zapping the specimen with either green or infrared laser light. The operator must choose the frequency that is best absorbed by the dirt but least absorbed by the specimen. A couple of zaps then vaporises the dirt leaving the specimen undamaged beneath. And the method is quick, too. A medium-sized piece, such as a football-sized wasps鈥� nest, can be laser-scrubbed in a matter of minutes.
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The technique鈥檚 success is not restricted to everyday grime, though. Cornish has tried it on leaves in the museum鈥檚 collection that were treated with mercuric oxide in the 1940s and 50s to kill pests. Although the chemical dealt with the pests, it left a residue that gradually turned black. Cleaning with the laser removed the residue and left the leaves unharmed. Using a microscope, it was even possible to identify tiny structural details such as the pores that allow gases to permeate the leaf.
Cornish has also removed a gold coating from microscopic fossils. Tiny marine organisms such as foraminifers and diatoms are used by geologists to date layers of limestone rock. But to identify the tiny fossils, researchers need to look at them under a scanning electron microscope, and that means coating them with gold. This coating is very difficult to remove except with chemical techniques, which are liable to damage the fossil. But the laser works perfectly.
The only specimens that cannot be cleaned are dung beetles, says Cornish, because the insects鈥� cuticle and the gunk coating it absorb the same wavelengths of light. 鈥淲e haven鈥檛 given up, though,鈥� she says. 鈥淲e鈥檙e going to try some different wavelengths.鈥�
Derek Pullen, head of sculpture conservation for the London art galleries Tate Modern and Tate Britain, says he is still evaluating laser-cleaning for use on their collections. He is convinced of the technique鈥檚 ability to clean, but wants to be sure that it does not leave the sculptures more liable to pick up muck in future. 鈥淲e have gone through various wonder treatments in the last few decades,鈥� he says. 鈥淢any have turned out to have hidden drawbacks.鈥�