The term "Mad Hatter" is popularly recognized from the character described in Alice in Wonderland by Lewis Carroll. He was the partner of the March Hare at the Mad Tea Party. Lewis Carroll did not invent the phrase, although he did create the characters. The phrases "mad as a hatter" and "mad as a March hare" were common at the time (1865) Lewis Carroll wrote Alice. The phrase "mad as a hatter" had been in common use in 1837, almost 30 years earlier. The Hatter and the Hare also reappear in Alice Through the Looking Glass as the King's messengers, Hatta and Haigha.

"In that direction," the Cat said, waving its right paw round, "lives a Hatter: and in that direction," waving the other paw, "lives a March Hare. Visit either you like: they're both mad." "But I don't want to go among mad people," Alice remarked. "Oh, you can't help that," said the Cat: "we're all mad here. I'm mad. You're mad." "How do you know I'm mad?" said Alice. "You must be, said the Cat, "or you wouldn't have come here."



Hatters really did go mad. The chemicals used in hat-making included mercurous nitrate, used in curing felt. Prolonged exposure to the mercury vapors caused mercury poisoning. Victims developed severe and uncontrollable muscular tremors and twitching limbs, called "hatter's shakes". Other symptoms included distorted vision and confused speech. In advanced cases, hatters developed hallucinations and other psychotic symptoms.

The popular top hat of the time was made from beaver fur, but cheaper ones used furs such as rabbit instead. A complicated set of processes was needed to turn the fur into a finished hat. With the cheaper sorts of fur, one step was to brush a solution of mercurous nitrate on to the fur to roughen the fibers and make them mat more easily, a process called carroting because it made the fur turn orange. Beaver fur had natural serrated edges that made this unnecessary, one reason why it was preferred, but the cost and scarcity of beaver meant that other furs had to be used.

Whatever the source of the fur, the fibers were then shaved off the skin and turned into felt; this was later immersed in a boiling acid solution to thicken and harden it. The acid treatment decomposed the mercurous nitrate to elemental mercury. Finishing processes included steaming the hat to shape and ironing it. In all these steps, hatters working in poorly ventilated workshops would breathe in (elemental) mercury vapor.



On December 2, 1955, the New York Times ran a full-column story, with a dateline from Danbury, Connecticut and headlines: "600 Hatters Mark 1941 Nitrate Ban." The story notes that "The occasion was the 14th anniversary of the outlawing of the use of nitrate of mercury in the hat industry." This notable event had come to pass since "On December 1, 1941, the United States Public Health Service brought an end to mercury's use by hat manufacturers in 26 states through mutual agreements." Credit for this achievement was claimed in whole or in part by the Public Health Service, the hat manufacturers, and the secretary-treasurer of the local union of United Hatters, Cap and Millinery Workers. Cynics have suggested that credit for this "triumph" should be attributed to a war-time shortage of mercury. For close to a century prior to 1955, the ravages of mercurialism among hatters had been known and tolerated in the United States.



So, what is written on the mad hatter's hat???