This mezzotint by William Pether, after the 1771 painting by Joseph Wright of Derby, shows a kneeling alchemist in his laboratory, gazing in wonder at the results of his latest experiment. The painting's full original title is “The Alchymist, in Search of the Philosopher's Stone, Discovers Phosphorus, and prays for the successful Conclusion of his operation, as was the custom of the Ancient Chymical Astrologers”. Wright's painting thus may represent the discovery of phosphorus attributed to the Hamburg alchemist Hennig Brandt in 1669. This popular story was printed and re-printed in chemical histories during Wright's lifetime. Phosphorus, a highly reactive element, emits a faint glow in the presence of oxygen, a response known as chemiluminescence. Here, the glowing matter in the alchemist's vessel throws the laboratory into stark relief, highlighting the edges of books and glassware and giving the composition an ethereal radiance.