The Mad World of Hat Making

Feb 19, 2021 0 comments

Hat-making in the 18th and 19th centuries was a hazardous business, because it involved the use of many chemicals, one of which was the toxic substance mercury. Working in poorly ventilated rooms, hat-makers breathed in so much mercury fumes that a good number of them were driven out of their wits by mercury-induced brain damage. Mercury poisoning among hat-makers is widely believed to be the origin of the proverbial saying “mad as a hatter”. Even the character of the Hatter in Lewis Carroll's iconic Alice's Adventures in Wonderland exhibited psychotic behavior similar to a person suffering from mercury poisoning.

John Tenniel's illustration of the tea party scene in “Alice's Adventures in Wonderland

John Tenniel's illustration of the tea party scene in “Alice's Adventures in Wonderland”. Accompanying Alice at the table is March Hare, the Dormouse and the Hatter.

Hats have been a fashion accessory as well as an essential and practical piece of clothing for thousands of years. But hat-making as an industry goes back by hardly four hundred years to the Italian city of Milan, where the finest hats from felt, fiber and straw were made. Merchants from Milan travelled across Europe trading silks, ribbons, braids, ornaments, and of course, hats, and passed on news of the latest fashion to aristocratic nobles. It is from Milan that the term “millinery” or hat-making comes from.

Mercury was first used in hat-making in France. Hat makers would take animal fur, usually from rabbit, and press them with steam and hot water so that the fibers matted together into a single piece of fabric. The French discovered that adding small amounts of mercuric nitrate to hot water roughened up the soft and limp hairs causing them to pack together more easily. The use of mercuric nitrate was a trade secret that was not revealed until the Huguenots were forced to flee to England to escape religious prosecution. In Britain the process earned the name of carrotting because treatment with the mercuric salt turned white fur reddish brown.

A worker at a Connecticut hat manufacturing plant treating a hat under water

A worker at a Connecticut hat manufacturing plant treating a hat under water. Photo: National Institute for Occupational Safety and Health/Wikimedia Commons

The most characteristic symptom of mercury poisoning is tremor; coarse jerky movements that usually begins in the fingers, then spread to the eyelids, lips and tongue. As conditions worsen, the tremors pass to the arms and legs, so that it becomes very difficult for a man to even walk. This condition was so obvious that it came to known as “hatter’s shakes”. The most remarkable change, however, is on the sufferer’s behavior. Irritability, low self-confidence, depression, apathy, shyness, timidity, and in some cases delirium and memory loss are seen.

A British Journal of Industrial Medicine article described the mad hatters’ symptoms in 1946:

The man affected is easily upset and embarrassed, loses all joy in life and lives in constant fear of being dismissed from his job. He has a sense of timidity and may lose self control before visitors. Thus, if one stops to watch such a man in a factory, he will sometimes throw down his tools and turn in anger on the intruder, saying he cannot work if watched. Occasionally a man is obliged to give up work because he can no longer take orders without losing his temper or, if he is a foreman, because he has no patience with men under him. Drowsiness, depression, loss of memory and insomnia may occur, but hallucinations, delusions and mania are rare.

In the most chronic cases, the hatter may suffer from mental confusion, emotional disturbances, and muscular weakness. Other symptoms include neurological and kidney damage, loss of hearing, bleeding from the ears and mouth, and loss of teeth, hair, and nails.

The connection between mercury and the mad hatter syndrome was first made in 1829 among hat-makers in St Petersburg, Russia. A thorough study of mercury poisoning among New Jersey hatters was made by the American physician J. Addison Freeman in 1860. In his groundbreaking paper, Freeman concluded that “a proper regard for the health of this class of citizens demands that mercury should not be used so extensively in the manufacture of hats, and that if its use is essential, that the hat finishers' room should be large, with a high ceiling, and well ventilated.”

Unfortunately, Freeman's call for prevention went unheeded.

Workers treating the fur with mercury nitrate in a felt hat-making factory

Workers treating the fur with mercury nitrate in a felt hat-making factory. Photo: National Institute for Occupational Safety and Health

By late 19th century, the hazards of working with mercury were well understood, but few hat manufacturers took any mitigative steps. In 1878, when Dr L. Dennis went around hat-making workshops around Essex questioning workers, many were hesitant to reveal their affliction for fear of losing their job. Even then, Dr. Dennis found that one out of every four workers were showing signs of mercury poisonings.

Most astounding was the lack of awareness among both the workers and their employers. Many hatters regarded the shakes as an inevitable price to pay for their work rather than a readily preventable disease. The government and the public remained largely indifferent, and the employers’ interests lay only in profits. The Second World War resolved the problem by making mercury too valuable to waste on felt hats. It was not until 1941, when the U.S. Public Health Service called for a voluntary ban on the use of mercury nitrate in favor of hydrogen peroxide.

# H A Waldron, Did the Mad Hatter have mercury poisoning?, British Medical Journal
# Richard P. Wedeen, Were the Hatters of New Jersey “Mad”?, American Journal of Industrial Medicine
# Susie Hopkins, History of Milliners, Love to Know
# Wikipedia


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