Fracture toughness of dried oil paints

The fracture toughness in opening mode for selected dried oil paints was determined filling in this way a critical gap in the knowledge required for the analysis of fracturing processes in paintings. The experimental work was made possible by the adaptation of the ASTM D5528–13 standard method to the size of available oil paints for a selection of oil paints from Mecklenburg's Paint Reference Collection now after approximately 30 years of drying. The careful regluing procedure allowed to improve the statistics of the measurements but also to get insight into in-depth profiles of the fracture toughness of some paints. The fracture toughness G IC values are the lowest for zinc white, raw umber and lead white with litharge, approximately 15 J/m 2 and the highest for sap green. The variable homogeneity of some tested paints – lead white, zinc white, sap green and verdigris – is reflected in the large range of the values obtained. This study demonstrated that some paints were more brittle than glue-based ground layers and as a consequence more vulnerable to cracking