The glass delusion was an external manifestation of a psychiatric disorder recorded in Europe in the late Middle Ages (15th to 17th centuries). People feared that they were made of glass “and therefore likely to shatter into pieces”. One famous early sufferer was King Charles VI of France who refused to allow people to touch him, and wore reinforced clothing to protect himself from accidental “shattering”.
The sufferer could believe or claim that he was any sort of glass object. A 1561 account reported a sufferer “who had to relieve himself standing up, fearing that if he sat down his buttocks would shatter… The man concerned was a glass-maker from the Parisian suburb of Saint Germain, who constantly applied a small cushion to his buttocks, even when standing. He was cured of this obsession by a severe thrashing from the doctor, who told him that his pain emanated from buttocks of flesh.”