Tackling conservation challenges using lasers

Laser cleaning is a non-contact technique and, as such, it has great potential for conservators faced with challenging situations. For example, some objects are too fragile to be handled or their surfaces are so delicate that they would be damaged even by gentle brushing. 

Using lasers for conservation projects comes with its own risks as they could cause burning or discolouration if their parameters are not finely tuned. They can also trigger physical and chemical changes to an object that are invisible to the naked eye. Lasers are routinely used on marble, sandstone and limestone objects to remove black pollution layers. However, little is known about the risks and benefits of using lasers to clean other materials or their effectiveness at removing other types of contaminants. 

In this project, a team of scientists and conservators investigated the use of the Museum’s Nd:YAG and Er:YAG lasers on a wide selection of artefacts. They began by testing mocked-up samples made from a range of materials so that adjustments could be made to the laser parameters. Then, scientists employed a full range of analytical techniques to determine whether lasers were appropriate for cleaning each of these materials. Finally, using these results, conservators safely ran tests on Museum objects.
 

This project has explored the use of laser cleaning in conservation to address the following challenges:

• Cleaning fragile and delicate objects, which could be damaged by gentle brushing.
• Removing old adhesives in conservation treatments that tended to yellow with time and become disfiguring. These need to be removed and replaced with more appropriate adhesives. However, unlike freshly applied adhesives, old adhesives are very difficult to remove using solvents.
• Removing so-called ‘cemented dust’. If not regularly removed, dust can accumulate and lead to the formation of a ‘sticky’ layer, which cannot be removed using gentle vacuum-cleaning and dusting and requires the use of solvents.
• Removing corrosion from gilded metal surfaces, which are easily damaged using conventional methods. 

The results of this project have been made available to heritage scientists and conservators to raise awareness of the potential of laser cleaning. This research has also been shared in journal articles and presentations at international conferences and a symposium at the British Museum.

The Er:YAG laser was found to be very effective for the removal of old adhesives from a wide range of materials (shell, ceramics and a late antique wall-painting). It was also successful at removing cemented dust from limestone and painted plaster, as well as old mould from Cypriot polychrome archaeological terracotta and limestone. Conservators managed to remove thick corrosion from a gilded archaeological silver object.  

Tests on feathers showed that white feathers could be laser cleaned effectively with the Nd:YAG laser but extensive damage was observed on dark feathers. The Er:YAG caused burning on all types of feathers.

The project has shared research outcomes in several blogs and a YouTube video on the British Museum’s channel. Laser cleaning has also been the focus of a showcase event in the Members' Room at the British Museum. 

The team working on the removal of mould from Cypriot archaeological terracotta received the Nigel Williams Prize for an outstanding conservation project in 2019.

Thanks to this research, laser cleaning is now used by British Museum conservators on a wide range of materials.