AIC's 42nd Annual Meeting

The deterioration of an early 15th century panel painting (originally from an altarpiece since dismembered) attributed to the Spanish artist Luis Borrassa, has been studied to devise a method to remove intractable restoration materials from the painting, particularly on the blue robes of the Christ figure, which appeared black.

Many panel paintings from the 14th to 16th centuries have come down to the present day with the original colors altered by previous restoration. This is especially true in the blue robes of Christ or the saints in which lapis lazuli or azurite blues are the primary pigment. Historically, the blue pigments are loosely bound and easily abraded when subjected to traditional solvent cleaning methods typically used for the removal of soot, wax, and natural resin varnishes. Often compounding the problem is the consolidation of the paint layer with animal glues and later with drying oils, which have often cross-linked and darkened, in some cases to almost black. This is further complicated by the addition of restoration paint and glazes to cover losses and abrasion.

This is the case with the Borrassa, where the blue robe of Christ looked essentially black. A half century ago in an unsuccessful attempt to correct the problem and conceal additional damages to the painting, a restorer applied a pigmented varnish of a dark amber color. The toned varnish imparted an overall uniform tone to the painting and cosmetically obscured the existing damages. In the current treatment, solvent methods were effective in removing the toned varnish from the painting, but not the composite layer of old consolidant, cross-linked drying oil, and restoration from the blue robes and other blue passages in the composition.

After extensive analytic studies the intractable restoration layer was identified by conservation scientists from the University of Pisa in conjunction with Duke University using GC/MS, FTIR, Scanning Electron Microscope and Microanalysis. The materials in the composite layer were identified as a combination of cross-linked drying oil and animal glues combined with natural resin varnish tinted with pigment. Testing was carried out successfully with the Er:YAG laser and the encrustation was removed or substantially reduced leaving intact the original lapis pigments.

This presentation will consider the analytic findings and demonstrate the Er:YAG laser methods for removing intractable materials without causing damage to the original surface. The Er:YAG laser operates at 2.94 microwatts, using pulsed laser energy to vaporize debris. The laser energy is confined to a surface depth of no more than a few microns, providing a natural barrier to energy penetration into underlying layers.