Clay ground in paintings: from Northern to Southern Europe

In the framework of the CATS' project to study the painting technique and materials in Dutch and Danish 17th Century artworks, several paintings were studied with a focus on the use and contents of red-brownish ground layers. SEM-EDX, FTIR and Raman analyses carried out on a group of selected paintings showed that some grounds consist mainly of clay containing quartz mixed with iron-based compounds. It is well known that clay is a sheet silicate mineral and may contain variable amounts of water trapped in its structure and can occur with other phases including quartz and carbonates [1]. The use of clay grounds containing quartz was first observed in the Netherlands in artworks from Rembrandt's workshop after 1640 [2] [3]. In addition, written sources of the same time period from outside the Netherlands mention this practice also in Italy and Spain [3]. The reason of using clay has still not been much investigated. Neither in the processing nor the trade of clays as a painting material. Did it give a particular colour/structure to achieve a specific final effect of the painted surface? Was clay cheaper than chalk, calcium sulphate or earth pigments? Did it give more flexibility to the painting support? Was it connected to the brick manufacturing? Was it a waste/reuse from the ceramic production? Based on that, some 17th century paintings from Italy belonging to the Statens Museum for Kunst (SMK) collection were surveyed by means of SEM-EDX analyses and FTIR and Raman spectroscopies to characterize the materials employed in the red ground layer. The investigation is aimed at demonstrating how widespread the use was of clays as painting material, comparing the analytical results performed on Northern and Southern European paintings. The preliminary study will lead to further research focused on the link between artistic schools of the period, the transmission of technology and knowledge of employing this type of clay grounds and, possibly, tracing the grounds and raw materials. [1]S. Guggenheim and R. Martin, Clays and clay minerals, 43 (2), 1995, 255-256. [2]K.. M. Groen, Netherlands technical studies in art, 3, 2005, 138-154. [3]K.. M. Groen, in "Rembrandt´s workshop and in paintings by his contemporaries", E. van de Wetering, Editor. 2011, Springer, Dordrecht.