The Donatello Pulpit

Seeing as how Ankush has covered the topic of linseed oil in the lunette case study, I will go ahead and discuss the other study mentioned in that same article by Spoto: the Donatello Pulpit.

Donatello's innovative work of art includes seven carved marble panels of the open-air pulpit that is located in the Duomo of Prato, completed in 1438. However, the pulpit had suffered from much deterioration since, due to its location outdoors. The central panel was in the worst condition as it was the most highly exposed to atmospheric agents, probably nitrogen oxides.

Because of the deterioration, many different methods were tried in hopes to preserve the artwork from even more degradation. After having no luck and additional degradation, the panels were removed and replaced by fakes.

Many think that the reason for further deterioration is due to the mixture of residues and degradation products formed which have led to deep cracks appearing all over the artwork. More specifically, architect Sanpaolesi's use of ZnSiF6 and MgSiF6 as a treatment for the deterioration had led scientists to hypothesize that these fluorosilicate compounds were the primary reason for the formation of the deep cracks. After performing the surface analytical technique, X-ray photoelectron spectroscopy (XPS), it was found that Sanpaolesi's treatment cannot be blamed solely for the formation of the cracks.

Procedures carried out to restore artwork should be properly tested prior to experimenting in order to avoid further deterioration. It just goes to show that one's best intentions can generate the worst results, a case shown in the restoration of Donatello's pulpit.

Here is a really cool diagram of how XPS works:
http://www.nuance.northwestern.edu/keckii/xps1.asp