Egyptian blue found in Romanesque altarpiece

A possible solution to the mystery

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.

The set of monuments made up by the churches of Sant Pere, Sant Miquel and Santa María de Terrassa are built upon ancient Iberian and Roman settlements, and the much-prized blue pigment could have remained hidden underground for many centuries. "But only a little of it, because this substance couldn't be replaced - once the ball was all used up the blue was gone", concludes Vendr

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