42nd Annual Meeting, Paintings & Wooden Artifacts Joint Session, May 31, "The Analysis and Reduction of an Intractable Coating for the Panel Painting by Lluis Borrassa, Christ Before Pilate," by William P. Brown & Dr. Adele De Cruz

The presentation by William P. Brown and Dr. Adele De Cruz was an awe inspiring glimpse at the future of conservation. Through the collaboration of the North Carolina Museum of Art and conservation scientists from the University of Pisa and Duke University, an intractable layer of cross-linked drying oil, animal glues, and pigmented varnish was removed from the surface of Spanish painter Lluis Borrassa’s panel painting, Christ Before Pilate, 1420-25.
The painting, which had not been exhibited for over 40 years, was the victim of previous cleaning and coating campaigns, and several layers of consolidation materials and paints and glazes had been applied to the blue passages of Christ’s robe. As a result of the cross-linking of these consolidants and the dark pigmentation of a conealing varnish layer, Christs’s robe appeared almost black.
During treatment at the North Carolina Museum of Art, solvents were successful in removing the toned varnish from the painting. However, the reduction of the complex layer of intractable material covering Christ’s robe (the abstract describes this as a composite of old consolidant, cross-linked drying oil, and restoration materials) was not so straighforward. Conservation scientists (from the aforementioned institutions) used FTIR, SEM, and GC-MS analysis to identify the components of the intractable layer and to discern them from original material, which consistsed of lapis, indigo, and orpiment pigments in egg tempera and glue or bee pollen.
Dr. De Cruz took the podium at this point in the talk to describe the methods used to reduce the intractable composite material. Essentially, laser ablation was employed, which before this talk I was only familiar with in the context of dentistry. I have to admit that my intitial reaction to hearing the terms ‘laser’ and ‘art conservation’ used together might have been a wary one, but a refamiliarzing with the techniques involved with laser ablation (and recalling the established use of this technique on the delicate enamel surfaces of our teeth) was an encouraging and exciting reminder of the vast potential of interdisiplanary approaches to art conservation.
Dr. De Cruz explained that the 2940 nm  Er:YAG (erbium) operates using an intense monochromatic wave of light (2.94 microwatts) at 15 pulses per second to vaporize the intractable material. The depth of penetration is very controllable, maintaining a shallow depth of penetration between 3-5 microns. This light pulse is highly absorbed by water, and produced a near instantaneous steam distillation. A glass cover slip is placed over the dirt, varnish, and paint layer. The laser is used to break up the intractable surface, which is ejected and contained by the glass cover slip. The debris is then swabbed from the surface of the painting and can be used for analysis.
There are several immediately obvious benefits to this method. It eliminates the need for toxic solvents, it allows for a highly controllable and low shallow depth of penetration. There is also no risk of chemical change to the substrate, and the reaction is low temperature.
Dr. De Cruz went in to incredible depth during this talk, and I realize that my summary only touches on the ammount of information she provided. I was furiously scribbling notes the entire time, and certainly wished I had a camera to take photos of her slides. I certainly look forward to hearing more about this topic in the future, and am excited for the future and ongoing collaboration of conservation and science.