Mercury was used in hat making to toughen the fur's fibers and make them mat together more efficiently. The compound used to moisten the fibers was Mercury Nitrate Hg(NO₃)₂, and the process is called carroting. It produced a superior-quality felt, which in turn, resulted in higher-quality hats.

Is mercury still used in hat making?

In some places in the world, Mercury, in small amounts, may still used in the felting process of men's hats. Most places, however, have found an acceptable alternative in Hydrogen Peroxide.

When did mercury stop being used in hat making?

The condition is called “mad hatter disease” because it commonly affected hat makers in the 18th to 20th centuries. They used mercury in the hat making process and developed mercury poisoning. Fortunately, hatters stopped using mercury in 1941.