Whilst experimenting with cleaning methods we gave laser cleaning a go.
Laser cleaning is becoming increasingly popular in conservation, particularly when dirt needs to be cleaned from very delicate surfaces such as textiles and paintings. The most commonly used laser cleaning systems in conservation emit short pulses of light, typically at a wavelength of 1064 nm or 532 nm. Light at this wavelength quickly and selectively heat the dirt on the surface, which expands and comes away.
In many cases, the light interacts only weakly with the surface of the object and the removal process stops as soon as the clean surface is exposed due to colour differences between the dirt and the surface. It is, therefore, possible to completely remove unwanted layers without over cleaning the valuable surface. This type of cleaning could be very useful for areas of bone that are very fragile and a method that did not ‘touch’ the surface and cause further damage would be advantageous – such as the underside of some skulls which has begun to peer away.
Although this cleaning method is often used on stonework and paintings there is very little research about it’s effect on bone – so we proceeded with caution and started our tests on some objects that had been up in the attic and were not of scientific importance. We chose items that would be very difficult to clean with traditional methods and so would be good subjects for laser cleaning. We had mixed results – in some cases it was very effective and removed dirt from surfaces that would otherwise have been awkward to clean. However, occasionally the laser failed to remove much dirt, or caused a change in colour of the original surface.
This may have been because lasers do not work on dark materials with lighter dirt cover - only the other way around! That's why lasers are often great for cleaning light \ greyish sandstone and marble with a black crust and that's exactly why we thought it could work on our bone material. Small tests have shown that dirty bone surfaces (without oil!) are easily and effectively cleaned with lasers.
Examples of laser cleaning: Swan feathers; the spikey skin of a flat fish; coral
As you can see the laser removed the dirt from the feathers but also discoloured them - making them yellow. The flat fish and coral however were successfully cleaned.
We then tried the laser on the stable surface of jaw of ‘Finn’, the Sei whale’s. The results however were not all we had hoped for. The laser did not damage the bone or change it’s colour which was positive but nor did it remove much of the dirt!
A square of oily whale bone after laser cleaning. Although some material has been removed dirt and grease remains on the surface.
China Laser cleaning machine
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