Abstract
In the Baroque European painting technology, various coloured clays had been used to prime canvases. These clays are generally considered to be carefully selected in terms of colour and other technological properties (adhesiveness, ductility etc.), as the painting represented the most delicate field of fine art.
However, it seems that the availability of the material at a given place as well as its price often played a much more significant role than previously thought. It led to the usage of highly heterogeneous cheap pottery clays in painting, even though they often had to be additionally coloured.
For the first time, a clear evidence is provided that a very similar pottery clay material was applied in three different technological ways: i) as a clay body of an unfired terracotta statue created in Florence or Bologna at the end of 16th century, ii) as a secondary putty on the Renaissance painting by Antonello da Saliba (1466-1535), and iii) as a preparation layer - ground - of an oil-on-canvas paintings attributed to Italian Caravaggists (17th century) or also to Carlo Maratta or workshop (1655-1713). The identity of the material was confirmed by mineralogical analyses as well as description of nannofossils, which enable to date the clay to Eocene - Oligocene.