Carolyn Riccardelli, George Wheeler, Christina Muir, George Scherer, and Joe
Vocaturo
Abstract
The use of pins or dowels in repairing stone has been common since ancient times. Conventional wisdom in art conservation suggests that repair materials such as pins or adhesives should have similar properties (such as strength and modulus) to the substrate. Stainless steel continues to be the most commonly used pinning material even though it has a much higher elastic modulus than that of marble. When planning the repair of a sculpture that will remain in a controlled museum environment, the reasons for choosing stainless steel (corrosion resistance, coefficient of expansion) become less important, and thus open up a wider variety of choices for pinning materials. Therefore, a set of tests was designed with the goal of determining the performance of a join using pins with reported moduli ranging from 0.5 to 197 GPa. These pins were set into Carrara marble cores using an epoxy resin adhesive and subjected to compressive-shear stress. Under these conditions, fiber-based rods such as fiberglass and carbon fiber out-performed both stainless steel and titanium in that they were of sufficient strength to withstand the maximum static forces of the sculpture being repaired and did not damage the stone core before pin failure. From these tests, the best-performing pinning materials were used in making full-scale stone mock-ups to evaluate the overall performance of a pinning/adhesive bond system.