One of the important aspects evolving from the treatment of leather objects is the presence of traces of copper and iron. These metals catalyze the degradation of leather by depolymerization of the collagen molecule. The paper discusses the different possibilities to prevent this type of reaction and a sequestering agent is chosen to bind the free copper and iron ions, considering the effect of the reaction products on the color of the leather. A series of tests is devised containing known amounts of copper and iron and the collagen shrinkage temperature is chosen as an indicator on the effect of the depolymerization reaction catalyzed by metal ions.