Like many well-educated men of his time, Gilles had an interest in alchemy. Alchemy, as you are probably aware, was essentially the attempt to turn base metals into gold, and to achieve immortality. In Medieval Europe, alchemy was associated with black magic, since it often involved the use of arcane symbols and processes, and many assumed that the avaricious and all-consuming search for gold must inevitably bring practitioners into contact with Satan. The strange sounds, smells, and equipment found in an alchemist’s laboratory would only have encouraged such Satanic associations. Consequently, the Church had outlawed alchemy by Gilles’s lifetime.
It is thought, paradoxically, that Gilles became interested in alchemy in order to save his soul from inevitable damnation, or at least delay it through immortality. Soon, his interest had turned into an obsession, and de SillÃ© and de Briqueville began procuring not only children but alchemists for Gilles. The most notorious itinerant alchemist Gilles entertained was FranÃ§ois Prelati, a clerk from Tuscany. Prelati impressed Gilles with his fluency in Latin and evidently high level of education. He claimed to have a demonic familiar named Barron, whom he would summon to assist him in his spells and incantations.
Although the alchemical-obsession came about because of Gilles’s murder of children, he did not, apparently, ever sacrifice any children to the devil. He did, however, allegedly use blood and dismembered body parts to assist Prelati in summoning Barron and casting spells. Unintentionally comic court testimony however makes Prelati sound like the archetypal con-man. For instance, Barron never appeared when Gilles was present, since he refused to sell his soul to the devil. And, for a demonic spirit, Barron showed a suspicious interest in mundane things: incredibly, Barron several times demanded that Gilles give Prelati money, and was unquestioningly obeyed.