John Martin’s paintings of biblical catastrophe met with a sensational response from the viewing public. Early in his career he was employed as a glass painter and this article examines the potential connection between this and Martin’s dramatically luminescent handling of light and dark and vivid reds. Others reworked several of his compositions as glass paintings and one example, of Belshazzar’s Feast, survives. These glass paintings have been aligned to the spectacular use of transparent media in popular entertainment and not credited with any art historical significance. Through direct comparison with the original oil painting, the glass painting of Belshazzar’s Feast is re-evaluated as a serious aesthetic experiment which, with the assistance of a magnifying glass as a viewing tool, used real light to amplify Martin’s use of light as his primary means of storytelling. Making a clear distinction between a Georgian glass painting and a Victorian stained glass window, attention is drawn to the technical virtuosity of the glass painting through reference to the working practice of the Edinburgh glass painter William Cooper, who reworked Martin’s Fall of Babylon on glass. Cooper’s writings are used to confirm a direct connection between the glass paintings and Martin’s reworking of his compositions in mezzotint and to investigate the complex nature of the materials and technical processes involved in their execution.