Many hats are made from felt, which is made by matting together the fur of small animals (typically rabbits or hares). Mercury nitrate is used to smooth out the felt, which can then be shaped.
The use of mercury in hatmaking is thought to have been adopted in 17th–century France, at a time when the dangers of mercury exposure were already known. The process was initially kept a trade secret in France, where hatmaking rapidly became a hazardous occupation. At the end of the 17th century (following the revocation of the Edict of Nantes) the secret was carried to England by the Huguenots.
The symptoms of mercury poisoning may include muscle weakness, poor co–ordination, numbness in the hands and feet, skin rashes, anxiety, memory problems, trouble in speaking, and trouble with sight or hearing.
The first description of these symptoms among hatters appears to have been made in St Petersburg, Russia, in 1829. In the United States, a thorough occupational description of mercury poisoning among New Jersey hatters was published locally by Addison Freeman in 1860. In Britain, the toxicologist Alfred Swaine Taylor reported the disease in a hatmaker in 1864.
During the Victorian era the hatters' malaise became proverbial, as reflected in popular expressions like "mad as a hatter" and the character of the Mad Hatter in Lewis Carroll's Alice in Wonderland. (In fact, Carroll's Mad Hatter is believed to have been inspired by Theophilus Carter, an eccentric furniture dealer, who was not a victim of mad hatter disease – although Carroll would have been familiar with the phenomenon of dementia among hatters.)
Alternatives to the use of mercury in hatmaking became available by 1874. In France, legislation was passed in 1898 to protect hatmakers from the risks of mercury exposure. By the turn of the 20th century, mercury poisoning among British hatters had become a rarity.
© Haydn Thompson 2017