In Arabic classifications of science and philosophy, which were adapted in the twelfth century, alchemy was defined as a sub-branch of natural philosophy (scientia naturalis), sharing this definition, above all, with medicine. Thus, about ten years after the first translation of an alchemical text into Latin (Morienus, De compositione alchimie), Dominic Gundissalinus described alchemy as belonging to physics in his De divisione philosophiae (ca. 1150). It was a science and an art aimed at the transformation of species
In the thirteenth century, representatives of Platonically-oriented cosmology and natural science such as Robert Grosseteste (1175-1253) defended a systematic use of geometrical representation. Following Grosseteste, “all causes of natural effects must be expressed by means of lines, angles, and figures, for otherwise it is impossible to grasp their explanation”. The corresponding theory of knowledge was neo-Platonic and Augustinian. The intelligible order underlying the physical, corporeal world was thought to be apprehensible by the divine part of the soul, by the ‘eye of the soul’, and geometrical figures (as well as number patterns) were used as ‘ladders’ leading to eternal truths.
The early fifteenth-century Aurora consurgens marks a further step in the elaboration of pictorial metaphors combined with glass vessels. The oldest and most spectacular copy of this document dates from the 1420s (Zürich, Zentralbibliothek, ms. Rh. 172). On a purely pictorial level, an inventive and high-quality artist developed a core of recurrent alchemical metaphors that relate to human and animal procreation, the dismemberment of bodies (symbolizing calcinations and putrefaction) and motifs such as the eagle and the dragon, which denote mercury as a volatile and as a solidified substance, respectively. In and around glass vessels, the artist metaphorically depicted stages of operation relating to the alchemical art of transformation as well as cosmological and philosophical principles of the art, such as “two are one” and “nature vanquishes nature”. Two or more principal metaphors are frequently combined within a single picture, reflecting the increasing use of chains of metaphors. For instance, one of the illustration combines the motifs of Mercury decapitating the sun and the moon with a vase filled with silver and gold flowers
Figure 11: Zürich, Zentralbibliothek, ms. Rh. 172, fol. 27v. Aurora consurgens (ca 1420-30). Mercury in the form of a serpent decapitating the Sun and the Moon. Gold and silver flowers in a vessel on the fire.
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