The durability of paints made with drying oil and alkyd mediums refers to their resistance to atmospheric moisture and solvents used in the cleaning of paintings. Ideally, after a reasonable drying period, these paints develop sufficient polymerization and cross-linking to resist swelling and deterioration from most cleaning solvents. Although there has been considerable research on the effects of certain metal ions on the autoxidation of drying oils, that research cannot be used to determine the long-term stability of paints made with drying oils. Current research suggests that a wide variety of metal ions affects the ultimate film formation of oil paints. The exact reaction of those ions with the drying oils is not clearly understood. But there is now considerable evidence that those metal ions are not only capable of migrating throughout a given paint layer but also sufficiently mobile to migrate from one paint layer to an adjacent one in a painting. In this case the migrating ions are capable of either enhancing or degrading the adjacent paint layers. Because artists’ alkyd paints contain considerable levels of drying oils, they can react with pigments in an manner analogous to oil paints and therefore will be part of this discussion.