Caitlin Breare’s excellent talk on the Monopoli Altarpiece, a seven-panel polyptych in the collection of the Museum of Fine Arts, Boston, was part of a morning of presentations focused on challenges encountered during treatment of painted wood. The fifteenth-century altarpiece originated from the city of Monopoli in southern Italy, but – as became clear during Caitlin’s presentation – it represents an amalgamation of styles. This city was on a trade route between northern Italy and the Mediterranean Sea, and both Venetian and Cretan painting clearly influenced the aesthetic. The altarpiece’s format and use of European poplar for the support is consistent with Italian construction, suggesting that a Venetian workshop may be responsible, while the painting materials and style are consistent with Cretan technique.
The treatment and research of this work, which had previously been deemed unexhibitable, was begun in 2015. Technical analysis revealed a great deal about the altarpiece’s materials and artist’s technique. Caitlin compared the work’s Cretan aesthetic to the Byzantine style with relation to the elongated figures and gilded background. The original gilding consists of burnished water gilding over a yellow ochre preparatory layer. While a yellow bole might be considered unusual in other contexts, this was a common material for gilders in Crete to employ. The use of a mixture of umber, black, vermilion, and white as a base tone for the flesh was also standard practice for Cretan painters.
Infrared reflectography showed that the underdrawing between the seven panels is consistent. Meanwhile, examination of the X-radiograph indicated the presence of scored lines under the paint in each panel, presumably to give texture to the wood before application of the gesso. Such scoring has been observed in the works of other Cretan painters. Examination of tool marks resulted in an exciting discovery: from the way the tool marks match up, the two panels with the saints directly on either side of Virgin seem to have been switched at some point in the past. Reconfiguring the panels also makes more sense compositionally, as the saints’ postures now direct the viewer’s eye towards the Virgin.
Restoration consisting of oil gilding was easily distinguishable from the original water gilding and was removed in the course of treatment. Treatment also involved grime removal and the reduction of a discolored, locally applied coating, probably consisting of drying oil; fortuitously, the coating appears to have protected the paint in some areas.
The greatest challenge encountered during treatment was the presence of calcium oxalate on the paint surface. The formation mechanism of this highly-insoluble brown layer is unknown, although Caitlin postulated that perhaps it may be linked to a coating applied over azurite. Another hypothesis is that fungus may be the source. In any case, chelators and mechanical removal were used to reduce the layer as much as possible. Now that the work has been cleaned, George Bisacca will be completing the structural treatment of the panels in the near future, and the altarpiece will be returned to the MFA for compensation.
For more on the altarpiece’s examination and conservation, there is a detailed summary on the MFA’s website: Conservation in Action: Monopoli Altarpiece. Although the language in the text is directed towards the general public, the post includes great images and time lapse videos of the treatment.
Study of the calcium oxalate layer and methods for its removal were prominent focuses of this treatment, and Caitlin hinted during the question and answer session that she will be looking further into medical techniques that reduce kidney stones as a potential solution for the removal of this type of layer. I look forward to seeing how Caitlin’s research progresses!