Raman spectroscopic analysis of the enigmatic Comper pigments.

An early church decoration project carried out by Sir Ninian Comper in 1896-98, involving the rood screen and canopy in St. Mary's, Egmanton, is currently undergoing restoration. Despite the rather prolific works of this famous ecclesiastical architect, there is little information available about the actual pigments that he used in his projects that gave rise to the special nomenclature "Comper green" and "Comper red". Specimens of green, red, black, grey, white and blue paint from this work have been made available for Raman spectroscopic analysis, and their identification has been achieved for the first time. The characteristic red and green pigments used in Comper's work, Comper green and Comper red, are both seen to be mixtures; in the former, Raman bands from chrome yellow (lead(II) chromate) and Prussian blue are identified, and the latter is confirmed as being a mixture of vermilion (mercury(II) sulfide) and barytes (barium sulfate). The other colours are found to represent a rich diversity of palette and include haematite, lead tin yellow (type II), lamp black, gypsum, anhydrite, hydrocerussite and calcite. The information from this first Raman spectroscopic study of Comper's palette will assist the conservation and restoration of an important nineteenth century church decoration.