When evaluating possible softening agents for parchment, it would be valuable to have a method for measuring stiffness in parchment before and after treatment. A sampling method was set up and many series of measurements carried out, using both a specially-designed accessory to a normal dynamometer, and an electronic stiffness tester. A relationship was derived between weight and stiffness for any bending angle which allows the deduction of stiffness from weight for standard samples of any given parchment. Thus the softening effect of a material on parchment can be derived from variations in stiffness after treatment. A formula is suggested for appraising the softening effectiveness index of an agent, taking into account the quantity absorbed by parchment. Diagrams, references.