Developing the use of Erbium: YAG laser

A conservator works on a picture frame in the studio

Hundreds of objects were treated during the Inspired by Knole conservation project carried out between 2016 and 2019.  With so many important 17th-century picture frames in the collection, the removal of old repairs undertaken in bronze paint, proved particularly difficult to achieve.

This was caused by the oil gilded surfaces having similar solubility parameters with the bronze paint. Conservators at the studio treated several gilded picture frames from Knole’s collection using an energy attenuated Fotona (Dualis XS) Erbium:YAG laser.

An English frame, probably dating from the 1630s, and reused for the slightly earlier portrait of Thomas Sackville was cleaned with the laser as part of the project. A range of approaches were taken for pre-wetting the surface, laser parameters, clearing with solvents and mechanically thinning layers disrupted by the laser. Using Er:YAG facilitated the partial or full removal of the bronze paint, while reducing the damage to underlying oil gilding associated with using solvents alone. 

After (left) and before (right) conservation of frame housing a portrait of Sir Thomas Sackville
After and before conservation images Sir Thomas Sackville portrait frame
After (left) and before (right) conservation of frame housing a portrait of Sir Thomas Sackville

Er:YAG has proven to be of considerable benefit in the removal of bronze paint from the oil gilding of the frames treated. Solvents which do not otherwise successfully remove bronze paint can do so when used to pre-wet a surface prior to laser exposure, and be used for clearing debris after its disruption. Two additional benefits of using lasers for these conservation treatments is the potential for reducing the use of toxic solvents, thereby cutting exposure for the operator and being environmentally cleaner. Continued collaboration between conservators and scientists, and disseminating research, is required to reach the full potential of this promising new technique.