CONSERVATIONISTS are employing laser technology to clean the 14th-century “Gallery of Kings” stonework on the western façade of Lincoln Cathedral.

The technology is being used to peel away centuries of grime on the figures of 11 medieval English monarchs, as part of a National Lottery Heritage Fund-backed project to restore the Cathedral and improve its visitor experience.

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The cathedral’s works department has already logged 93,000 hours since 2016 on the west front alone. The equipment being used at Lincoln gently removes centuries of carbonate and sulphate pollution, which causes dark patches on the stone surface. The power of the laser beam is set at a level low enough to break the molecular bonds in the pollution layer, effectively vapourising it, without abrading the stone below.

The technique is also being used on the Romanesque frieze: a 12th-century series of one-metre-tall panels running across the western façade, depicting scenes from heaven and hell and messages from the Old and the New Testament, and on the great west door, the oldest part of the building, which also dates from the 12th century.

The work is part of a £16.5-million project, which includes a new visitor centre, due to open later this year, which will display replicas of the frieze.

The director of works and property at the cathedral, Michael Sheppard, said: “These are the first substantial works to the west front since the 1980s, and, by implementing innovative and cutting-edge conservation practices and techniques, it will be protected for decades to come.”

A spokeswoman for Historic England said that lasers were first used for conservation in the 1970s, and have been used in locations as varied as the Grade I listed St Mary’s Priory, at Tutbury, Staffordshire, and the Canadian Parliament buildings in Ottawa.

“This technique is used when other cleaning techniques, such as water, are not suitable, or a sensitive method is needed. It is an expensive technique, because of the cost of buying or hiring the equipment, and the rate of cleaning is relatively slow. However, it can be very effective on delicate or intricate surfaces, particularly where there is a contrast between the soiling and substrate.

“Although it a is sensitive and adjustable technique, the effect of the laser beam can still cause damage: for example, some polychrome pigments can be oxidised, causing discolouration, so needs skill and expertise to use it appropriately and effectively.”