Laser scanners becoming central to stone conservation

Merseyside museums lead the way in applying new technology to stone conservation



With the growing problem worldwide of stone decay caused by atmospheric pollution, conservators are turning to modern technology for quicker and more accurate ways to record what is still extant for posterity. The National Museums and Galleries on Merseyside, which houses Britain’s leading stone and sculpture conservation centre, is the first in this country to install the most recent development—a laser scanner. Originally invented for high resolution engineering and plastic surgery, the scanner, which employs a low-energy helium-neon (He-Ne) laser, can measure an object three-dimensionally to within a millimetre of accuracy. The scanner is usually fixed to a circular platform on which the subject is placed. It is motorised so that it can rapidly circumnavigate the platform, measuring distances by trigonometry as it moves—to record a human head can take as little as fifteen to twenty seconds. The information is fed directly into a computer and the digitised information printed out as a linear contour map or as a solid representation in light and shade. Not only do accurate 3-D computer models allow information on cleaning, damage and repair to be superimposed as a record of the state of conservation of a work of art, they also allow tailor-made packing cases to be constructed for its transportation. A more exciting spin-off still is that by feeding the digitised information into a computer-guided lathe it is possible to carve reproductions of sculptures in a variety of materials, such as wood, plaster, glass or stone. This process has already been applied to a severely weathered stone head from Lincoln Cathedral. In the past much damage has been done by taking moulds from sculptures in museums and elsewhere. To be able to make an accurate replica of a sculpture without touching its surface has far-reaching implications, both for the museum replication industry and for open-air sites where stone sculpture is suffering from irretrievable decay. In Florence, for example, statues have been taken down and housed in museums with replicas being put in their place. The same may happen on the Acropolis, where the marble of the Erechtheum and the Parthenon is under attack from acid rain caused by air pollution, as well as the growth of a black fungus within the marble encouraged by hotter, drier weather over the past fifty years. Lasers are also being used to vaporise the dirt from limestone and marble sculpture. John Larson, Head of Inorganic and Sculpture Conservation at the National Museums and Galleries on Merseyside, who is also pioneering the laser scanner, has been using a type of laser developed by Loughborough University in a trial run to clean the limestone sculptures at Lincoln Cathedral. The light from the laser is absorbed by the black dirt as energy and the heat generated burns off the carbon particles adhering to the stone. When the laser reaches the pale stone surface the light emitted is bounced back instead of absorbed and the process ceases. At Loughborough it has been found that the optimum type of laser for this purpose is a yttrium-aluminium-garnet crystal containing traces of the element neodymium. The Merseyside museums have now ordered a neodymium laser for their conservation department, the £10,500 cost to be paid by the Henry Moore Foundation.

Originally appeared in The Art Newspaper as 'Laser Sculptors'