Surveying a Sixteenth-Century Full-Scale Working Drawing. The Tracing for the Sail Vault at the Vestry of Murcia Cathedral

Abstract

Full-scale tracings, drawn in plaster surfaces or engraved in stone walls and floors, were used frequently in Renaissance construction, in order to control the execution of ashlar masonry. In many occasions, these tracings furnished the shape of the templates used in the dressing process, either in true size or orthogonal projection. A large example of these tracings appeared in 2009 in the vestry of Murcia cathedral, when the sacristy drawers were disassembled in order to execute a conservation treatment against woodworm. At first sight, the tracing seemed to be related to the vault over the vestry, built in 1525 by Jacopo Torni l'Indaco, one of the first examples of ashlar sail vaults in Europe; a number of surveys confirmed that the tracing corresponds with the vault quite precisely. After an introductory section dealing with tracings and dressing techniques, the authors explain the measuring methods used in the surveys, describe the tracing, compare the tracing and the built vault, and discuss the relevance of the tracing for the history of dressing methods in European ashlar masonry.