Observations on dimensional changes of sized canvas based on glue temperature

The aim of this study was to explore dimensional changes caused by water on sized canvas. Samples of new linen canvas were mounted on a rig for biaxial tensioning, holding a constant stress of 100 N/m in both weave directions. The samples were then sized with respectively warm fluent glue (45 °C) or a cold gel (20 °C), both consisting of a 5 percent sheepskin glue extracted from parchment clippings. The warm glue was absorbed into the canvas structure, whereas the cold gel mostly stayed as a discrete layer on the canvas. Twice the amount of glue was therefore needed for the warm sizing. When the size had dried, water was applied to the back of the canvas with a brush and the dimensional changes were measured. The results showed that the samples that had been sized with cold gel shrank significantly more than the samples that had been sized with warm glue. This is due to the differences in the degree of penetration and subsequently in the amount of glue fixating the structure of the canvas. Furthermore, the water content of the warm glue resulted in relaxation shrinkage of the canvas during sizing and thereby reduced the intrinsic stress in the canvas. The results suggest that the temperature of size layers during application is important to the dimensional reaction of a canvas painting that is exposed to water.