PVC films containing methyl violet have been subjected to UV irradiation to induce dehydrochlorination leading to capture of the released HCl by the dye. It is demonstrated that a process similar to the indicator colour change in an aqueous solution can also be induced within the PVC matrix by the action of light. It is also shown that this process can be utilised for lithographic purposes. © 2000 Elsevier Science Ltd. All rights reserved.