There was a time when lasers were the latest of latest marvels to hit the scientific scene. We marvelled at these amazing devices that could project a beam of light from earth onto the moon or which could burst a coloured balloon inside a clear one, could cut through steel, carry thousands of telephone messages or provide undreamed of accuracy for surveyors. There was even a time when giant lasers in space were going to shoot down Russian missiles with unprecedented reliability and accuracy, thus eliminating the "Red Menace" once and for all!
I can remember the awe with which I saw my first laser in a laboratory and the precautions my friend the laboratory assistant took when handling this dangerous and temperamental beast. How times change! Now not only do I carry a laser in my pocket to be used as a pointer when I am giving slide lectures, but I listen to music played on minidisk read by laser light and these words will eventually be archived onto a DVD, written by yet another laser. Now archaeological conservators are discovering that the laser has uses for them as well.
One of the most striking characteristics of lasers is that they produce light of a single wave-length. The ordinary tungsten bulb produces a wide range of wavelengths, all mingled together to provide the yellowish glow we think of as white light. Even fluorescent lights, although they work with a far more restricted palette, provide more than one frequency of light. Lasers, however, produce one single frequency.
This means that the heating effects of such intense light can be closely tailored to the object in question. For example, an infra-red laser whose wavelength is 1064 nanometres is ideally suited to cleaning ancient documents: the soot from smoking lamps and the grease from unwashed hands vanish instantly, evaporated by the heat they absorb from the laser, while the precious parchment underneath remains untouched and unscathed. (Quite what happens when you pass the light over a passage written in black ink produced from soot and lamp-black, I do not know, but I am in no hurry to find out by experimentation on any priceless manuscripts I may happen to have.)
The same applies to the layers of grime that have accumulated on the surface of statues exposed to modern pollution. Whereas Lord Duveen's workmen with their wire brushes and blocks of pumice could not distinguish between dirt and patina, a laser can. It is now possible to clean the Elgin Marbles - were that considered desirable - without touching the stone beneath the dirt.
Lasers, however, have other characteristics. Just as a laser can read the tiny pits and hollows on a CD, so it can read the somewhat grosser bumps and crevices of an ancient sculpture, providing a digital recording of every detail. This has two uses: in the first place, it is now possible to produce a copy, accurate to 0.1mm of an ancient sculpture without ever touching the original.
Museums around the world have long featured reproduction artifacts in their shops and almost invariably these have been produced from rubber or plaster moulds. Not only is this a time-consuming procedure, but the process of making the mould carries the risk of damaging the original. It was simply not possible to make moulds of objects that were fragile or in a poor state of preservation, no matter how desirable such replicas might be in the eyes of the buying public. Over time the mould wears out and then the museum authorities are faced with the nice judgement of whether to venture the risk and expense of making another.
Now, however, a perfect replica can be reproduced of any object, no matter how fragile, by scanning it with a laser. By using a modern milling machine linked to a computer disk of digital information, endless replicas can be produced without any degradation of the mould.
The second use is less financially viable but may well be even more important. No matter how carefully a statue is preserved, in an increasingly polluted world its surface will suffer degradation and damage. With due care the process can be slowed down sufficiently that the damage is all but imperceptible and then comes the problem of trying to remember whether a statue seen in one's youth is different to what is seen in one's old age. Was the detail in the hair more sharp than it is now or is memory playing tricks? Even photographs may not be of use, for lighting may obscure the details in which one is now interested or the photograph may be taken from the wrong angle or from too far away.
Now, however, vulnerable objects can be scanned and the digital data preserved by some suitable means and in a thousand years time a milling machine can produce a faithful copy of the original against which the preserved statue can be compared.
Here, surely, is the solution to the problem of the Elgin Marbles and all the other objects whose possession is disputed. Produce accurate replicas of them to be displayed for the public and lock the originals away in clinical conditions best suited to their preservation. The Greeks can have the marbles back on the Parthenon, knowing that when the Athens air gets to them more can be produced, and the British Museum can have the marbles in the Duveen Gallery for the grubby-fingered populace to gawp at and finger to their hearts' content. Meanwhile the originals can be safely stored in Sweden or Outer Mongolia or some other location where the air is clean, the political conditions are stable and the general population have no interest whatsoever in them.