He was trained in the workshop of Verrocchio, who according to Vasari, was an able alchemist. Leonardo was a chemist in so much as that he experimented with different media for suspending paint pigment.
Leonardo's training under Verrocchio's guidance placed him within the realm of alchemical knowledge, as noted by Vasari. Furthermore, his work as an artist involved chemical processes, such as experimenting with different mediums to suspend paint pigment.