The purpose of this study was to test the possibility of stabilizing pigmented dammar and Ketone Resin N formulations against yellowing and loss of solubility, thus allowing their use as inpainting materials. Four propagation suppressors were chosen, one for use with dammar and three with Ketone Resin N. The synergistic pairing of one of the latter additives with an ultra-violet absorber was also tested. Both stabilized and unstabilized formulations of the varnishes were prepared. From these, two sets of films were cast on glass slides, with and without inclusion of eleven different pigments. One set was reserved for natural ageing, and the other was aged for about 830 hours in a light box fitted with black light fluorescent and cool white fluorescent tubes. Measurements were taken on a Hunterlab Color Difference Meter before, during and after ageing. Changes in solubility were also tested by attempting to remove the aged films with a series of 10 solvent mixtures of increasing strength, and comparing the solubility parameters of successful solvents for corresponding aged and unaged samples. Under the conditions of ageing applied here, dammar showed increased yellowing and difficulty of removal with the addition of the stabilizer Irgenox 565. The behaviour of Ketone Resin N showed a range of improvements with the range of additives. The best results were obtained with Tinuvin 770, and with the pairing of UV absorber Cyasorb UV 24 with a propagation suppressor. Pigments clearly influenced the discolouration and loss of solubility of dammar and Ketone Resin N films. Only a stabilizer that proved consistently effective across the range of pigments would be really useful. If the effectiveness of Tinuvin 770 and of the synergistic pair could be confirmed by overcoming uncertainties surrounding the relevance of artificial ageing, then these and other additives could make Ketone Resin N a stable inpainting medium.