Egyptian blue pigment has been found on a 12th century altarpiece in a chuch. The pigment was used in ancient Egypt up until the end of the Roman empire. So how could it turn up on a medieval artifact?
“We carried out a systematic study of the pigments used in the altarpiece during restoration work on the church, and we could show that most of them were fairly local and ‘poor’ – earth, whites from lime, blacks from smoke – and we were completely unprepared for Egyptian blue to turn up”, Mario Vendrell, co-author of the study and a geologist from the UB’s Grup Patrimoni research group, told SINC.
The researcher says the preliminary chemical and microscopic study made them suspect that the samples taken were of Egyptian blue. To confirm their suspicions, they analysed them at the Daresbury SRS Laboratory in the United Kingdom, where they used X-ray diffraction techniques with synchrotron radiation. It will be possible to carry out these tests in Spain once the ALBA Synchrotron Light Facility at Cerdanyola del Vallés (Barcelona) comes into operation.
“The results show without any shadow of a doubt that the pigment is Egyptian blue”, says Vendrell, who says it could not be any other kind of blue pigment used in Romanesque murals, such as azurite, lapis lazuli or aerinite, “which in any case came from far-off lands and were difficult to get hold of for a frontier economy, as the Kingdom Aragon was between the 11th and 15th Centuries”.
The geologist also says there is no evidence that people in Medieval times had knowledge of how to manufacture this pigment, which is made of copper silicate and calcium: “In fact it has never been found in any mural from the era”.
“The most likely hypothesis is that the builders of the church happened upon a ‘ball’ of Egyptian blue from the Roman period and decided to use it in the paintings on the stone altarpiece”, Vendrell explains.