Mary Witkop and Mitchell Pluto collaboration 1998 

Vessels: methods of containment. Can you take the heat? Are you opaque and dense, slow to warm so no one can tell what is going on inside? Sometimes it is less an issue what is in the vessel, the nature of the stuff being contained, and more one of shape: leaky, fragile, brittle, solid, full to overflowing, empty, cracked 

Alchemical Psychology. James Hillman