This paper focuses on finding an inert formulation for pigmented wax-resin infills to be used for oil paintings on copper. Two pigmented wax-resin formulations currently in use are characterized: one supplied by one of the authors (C-PWR) and the other, a commercial product, Gamblin Pigmented Wax-Resin sticks (G-PWR). While both have excellent properties, they contain natural beeswax which has been reported to result in corrosion where in contact with copper. Acid number measurements confirm that both are acidic. Although ageing tests are still needed, the characterization and properties of two new formulations, both based on Techniwax 9426 microcrystalline wax with either Regalrez 1094 or 1126, are promising. Bothe new wax-resin mixtures, with an acid number of 0, are likely to be inert in relation to the copper and are anticipated to be chemically stable due to their composition.