The bricks of Hagia Sophia (Istanbul, Turkey): A new hypothesis to explain their compositional difference

The work shows the results of a multi-analytical study performed on twenty-nine brick samples takenfrom Hagia Sophia in Istanbul (Turkey). Hagia Sophia, one of the most important historical buildings inthe world, has a very complex construction history. This complexity is also reflected in the materials thatwere used for its construction. The main purpose of this work is to verify whether there are any compo-sitional differences in the bricks used in different historical periods, but also to understand the reasonsfor any compositional differences between one period and another. The samples were studied by opti-cal microscopy (OM), X-ray fluorescence (XRF), X-ray powder diffraction (XRPD) and thermogravimetricanalysis (TGA), coupled with a new approach, based on the micro-chemical EDS analysis used to obtaininformation on the clay fraction of the matrix. The study showed that, most probably, the differencesbetween the bricks belonging to the different construction phases are due to the composition of the claysused for their preparation.