The Philosophers Observing the Boiling Vessel

On the left, a crowned king in a long blue robe over green hose stands alongside two men, one in a pink tunic and one in a bright green robe. The figure in the green robe and the king both gesture with their hands toward a large, pear-shaped ceramic pot on the right, which is being heated by flickering red flames. The scene is set against a dark, featureless background, and the painting is rendered in a flat, illustrative style typical of 15th-century manuscript illumination.

This image originates from the 'Aurora consurgens', an important 15th-century alchemical treatise attributed to a pseudo-Thomas Aquinas. It illustrates the 'Great Work' or the process of transmutation, where the heating of materials in a vessel (the athanor) serves as a visual metaphor for the refinement of matter and spirit.