The bubbles present in the back of the cyclophosphamide cast were a happy accident: normally this is avoided in the glassmaking process through careful annealing, but we were so enchanted with the effect when it emerged from the kiln that we decided to keep it. We annealed the remaining casts differently, though.

Mustard gas is normally colourless (the name derives from its pungent, peppery smell), but we decided to paint the bubbles yellow for better visibility.