Many alchemists are known from the thousands of surviving alchemical manuscripts and books. The sigil is reproduced in "Dictionary of Occult, Hermetic and Alchemical Sigils" by Fred Gettings. The treatise concludes with an alchemical poem. The writings attributed to Hermes Trismegistus are a primary source of alchemical theory. The homunculus continued to appear in alchemical writings after Paracelsus' time. Some alchemical theories were closely related to numerology. The discovery of gunpowder was probably the product of centuries of alchemical experimentation. Cleopatra is used as a character within the dialogue of the alchemical texts themselves. The magnum opus had a variety of alchemical symbols attached to it. Bacon has been credited with a number of alchemical texts. Sulfur was considered important enough to receive its own alchemical symbol. Its alchemical symbol is encoded at U+1F750. There is little evidence that Ashmole conducted his own alchemical experiments. A great deal remains to be discovered about Indian alchemical literature. This listing includes creatures that are man-made, mechanical or of alchemical origins.