The investigation and application of laser

Project leader: Capucine Korenberg

Department: Conservation and Scientific Research

Project start: January 2006
End date: January 2009

Other British Museum staff: Alexandra Baldwin, Karen Birkhoelzer

External partners:

Professor Costas Fotakis and Dr Paraskevi Pouli from the Institute of Electronic Structure and Laser of the Foundation for Research and Technology-Hellas (IESL-FORTH) in Crete. http://www.iesl.forth.gr

Project funded by:

A two week study trip to FORTH was supported in part by the European Commission through the Research Infrastructures activity of FP6 (“Laserlab-Europe” RII3-CT-2003-506350").

Description:

The Museum has recently acquired a dual wavelength Nd:YAG laser with the generous support of Mr Ed Teppo. Laser cleaning is an established technique in stone conservation to remove pollution crusts, but studies have shown its potential for use on other materials such as paintings or parchment.

This project looks at the use of laser on materials across the collection of the Museum. Currently, the use of laser to clean Egyptian painted surfaces (coffins, murals etc.), archaeological copper alloy artefacts and historical iron artefacts is under investigation. Since laser can induce damage to objects, tests are done either on modern replicas or on unregistered objects. Laser parameters such as energy and wavelength need to be optimised for each material and some of the tests were carried out at the Institute of Electronic Structure and Laser of the Foundation for Research and Technology-Hellas in Greece, which has extensive laser facilities.

As well as obtaining visually satisfying results, it is essential to determine that laser cleaning does not have any adverse effects. For example, laser cleaning can appear to be very effective at removing tarnish from metals. However, when laser cleaned surfaces are examined at very high magnification using a scanning electron microscope, there is sometimes evidence that melting has occurred at a microscopic level. For each material examined in this project, laser cleaned surfaces will be examined using a range of analytical techniques. The long-term effects of laser cleaning will also be investigated as required.

Objectives:

Laser cleaning has many advantages compared to traditional techniques. The diameter of laser beam can be adjusted so that small areas can be cleaned, making laser a very accurate technique. There is no physical contact between the laser equipment and the object to be cleaned. Therefore, laser is an interesting technique to clean fragile objects. Also, in many cases laser is a selective tool: it removes dirt, without affecting the original material underneath.

Laser is very effective at removing pollution crusts from stone objects and has been used in conservation since the mid 1990s. The aim of this project is to determine whether laser is a suitable cleaning technique to conserve materials other than stone. If the outcome of this project is positive, laser-cleaning can be added to the range of techniques used for cleaning painted Egyptian artefacts, archaeological copper-alloys and historical iron objects.

Publications:

C. Korenberg, ‘Laser cleaning tests on archaeological copper alloys using a Nd:YAG laser’, with A. Baldwin, Laser Chemistry, vol. 2006 (2006) Article ID 75831, seven pages

Images (from top):

• One of our collaborators, Dr Pouli, setting up laser cleaning tests at FORTH in Crete. 
• Melting on the surface of a sample of archaeological copper alloy caused by laser irradiation (horizontal field of view: 3.5 mm).
• Discolouration of relagar paint after laser irradiation (horizontal field of view: 13.5 mm).
• A conservator from the British Museum conducting laser cleaning tests on an iron sample.