Brittleness dammar

Sticky waxes are generally composed of resins and wax. A high resin content gives viscosity to the melt, a long plastic range, and a brittle fracture when cooled. No modem formulas are available, but the older recipes usually had rosin, beeswax, and gum dammar as the essential constituents. 

Feller, R. L. (1958). Dammar and mastic varnishes hardness, brittleness, and change in weight... 

---