In paintings conservation, examination of the back (verso) of a painting can provide invaluable information and insight about the artwork. For example, the verso of a canvas may reveal stamps indicative of the manufacturer, or even hints of the life and provenance of the painting. Likewise, careful study of the back of panels, such as those used to create the Monopoli Altarpiece, may reveal evidence on how the boards were made.
In 1939, restoration carried out at the MFA included the application of a wax mixture, consisting of beeswax and resin, to the verso of the altarpiece panels. This was done to help stabilize the wood and provide a barrier against moisture in the environment, with the goal of preventing the wood from warping.
The decision to now remove the wax is based on several factors. On a practical level, its presence is an impediment to structural work that will be carried out in the coming months. No less significantly, the surface of the wood below the wax carries evidence of the tools used to create them, as well as traces of pigments and incisions that may relate to patterns, all of which can provide scholars with useful information about the process of making these panels. A characteristic that makes these panels special and aids in their study is that they have never been thinned down. The practice of thinning down panels was common in the past, and it is relatively unusual to find panels of this age that are intact.
Removing the wax from the verso of the panels is a two-stage process. First, the bulk of the wax is carefully removed using a scalpel, held almost parallel to the panel to prevent damaging the surface of the wood. Although the wax is relatively soft, this process quickly dulls the scalpel blades, and they need to be replaced with surprising frequency. To complete this step, a total of 25 blades were used over approximately 19 hours.
With the wax shaved down as closely as possible to the surface of the wood, solvent is introduced to reduce the wax further. After a series of tests, the ideal solvent is selected and applied in a gel. The solvent gel is spread onto the surface using a wide brush and allowed to sit in contact with the wax for 3-5 minutes. The gel is then agitated using a cotton swab, before being rubbed off of the surface. Remaining gel residue is removed using a cotton swab dipped in free solvent. In total, reduction of the wax from the verso of the panel required approximately 34.5 hours to complete.
As seen above in the after treatment images, removal of the wax coating produces a dramatic change in the appearance of the surface of the wood, revealing many details and textures that were previously obscured. At left is an image taken in normal light; at right is the same panel pictured in raking light (lighting from only one direction at an oblique angle so that surface topography may be better visualized). Below, incisions on the back of the panel may be seen clearly in a detail image taken in raking light.