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“Clay grounds” in Denmark: from soil to canvas
In the framework of the CATS’ project to study the painting technique and materials in Dutch and Danish 17th Century paintings, with a key interest on the materials, techniques and trade of artists’ practice in Denmark, several paintings, of which some are attributed to the Danish-born Dutch painter Pieter Isaacsz (1569-1625), were studied with a focus on the use and contents of red-brownish ground layers. Written evidence state that Pieter Isaacsz, on several occasions, imported painting materials from the Netherlands to the Danish Colour Chamber, and he also had a central role, together with several other foreign painters, in the decoration of the long hall at Rosenborg Castle. They produced a series of large paintings ordered by King Christian IV, the so-called Rosenborg Series, of which 13 out of 15 preserved paintings have red-brownish ground layers of various tonalities.
Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FTIR) analyses on a group of pre-selected paintings attributed to Isaacsz and four other painters working on this large decorative scheme showed that at least two grounds from those paintings consist mainly of clay mixed with iron and magnesium-containing compounds. Furthermore, both SEM-EDX and µRaman measurements clearly highlighted the presence of a large amount of quartz particles. 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.
Studies carried out by Kühn and Groen and summarized by the latter show that in the Netherlands this kind of preparation layer was first observed in artworks from Rembrandt’s workshop after 1640. Written sources from outside the Netherlands -such as Francisco Pacheco and Pierre Lebrun- mention this practice, also before Rembrandt's time. It was known that clay was cheaper than chalk or earth pigments and it gave more flexibility to the painting support allowing for the canvas to be rolled during transport; it is therefore possible that Rembrandt got this idea from others. Moreover, it is interesting to note that in the same sources cited above “potter´s earth” and “earth used for making bricks” are mentioned, suggesting a connection with potters and brickyards or earthenware factories.
After the initial results, more samples from the Rosenborg series will be analysed in order to investigate further the ground composition and the diffusion of the clay ground in Denmark. These preliminary analyses will lead to further research focused on the link between the Netherlands and Denmark concerning the use of this type of priming layer in Northern-Europe, the link to earthenware or tile/brick production and, possibly, tracing the origin of the raw material.