Understanding 17th-18th century Dutch Tin-glaze Through the Interpretation and Reconstruction of Historical Recipes

Historical glaze recipes can provide important information on the source materials used for glaze production and insight into the working practices of potters as well variations in glaze characteristics that may help us understand susceptibility to glaze deterioration. This research focusses on an 18th century hand-written recipe book by P. Sijbeda which describes over 75 (primarily) Dutch tin-glaze recipes dated between 1659 and 1755 and used for both tile and object production (Figure 1). The recipes give details of the sources and quantities of the raw materials needed to produce tin glaze, then made from two components: Masticot (a glass produced from sand and fluxes) and tinas (tin- and lead oxides used for their opacifying and fluxing qualities). The variations in the recipes provide important information: how glaze recipes have changed over time, the fact that different glazes were used for tiles and objects, and the deliberate production of different qualities of glaze. The glaze recipes described in the book have been compared with other historical tin-glaze recipes (Biringuccio, Piccolpasso, Diderot, Paape and Bastinaire-Daudenart) and their applicability assessed using modern calculation techniques such as the Seger formula. The interpretation of the raw materials as described in the recipes and their probable sources has been supported by research into the raw materials available at the time together with the results of semi-quantitative analysis (SEM-EDX) of twenty 17th and 18th century Dutch tiles. This combined research has led to significant findings, in particular regarding the source, composition and use of fluxes used in the recipes, the composition of the sodium carbonate or soda (from Alicante or Scotland), as well as the common salt added to the final frit, which is described in written sources as being essential to obtain a whiter glaze colour. Three historical tin-glaze recipes have been reconstructed: a high-quality and a low-quality glaze from the Sijbeda book. The glaze recipes were created using pure chemical components, taking into account SEM-EDS analytical results. The glaze reconstruction protocol followed the historical process as closely as possible within the feasible health and practical limitations, the components of the Masticot recipes and final glaze being mixed and fired on a sand-bed on the bottom of the kiln. The influence of common salt (sodium chloride) was assessed by creating two recipes using sodium carbonate and sodium chloride. The firing protocol (temperature, firing time and soaking period) was formulated from what is known about both the kilns and firing procedures of the period. The glazes were applied to ceramic test tiles that had already been produced from historical clay recipes. The results of the recipe interpretation, glaze reconstruction and preliminary glaze tests (figures 2 have provided new insight into the composition and effect of raw materials used in Dutch tin-glaze production, in particular the fluxes (soda and potash) and common salt which appears to have a bleaching effect. Furthermore, this research has led to a better understanding of the production and firing process and shown that different recipes were used for objects and tiles