A technique called Carroting was being used from the mid of the 17th century to the mid of the 20th century. This process allowed to make good quality felt which was used to make hats for men. The skin of hares, rabbits, and beavers were used and were processed with a dilute content of mercury compound known as mercuric nitrate.
The animal skins were put in the oven and dried, in this process the skin on the sides turned orange, similar to the color of carrots. The skin was then placed under a cutting machine and was sliced into thin shreds. The fur was blow dried on a conical shaped colander and there after dipped in boiling water to keep the shape as it is. The cone was then removed and passed under a wet roller to turn the fur into felt. The hoods that were derived in the process were blocked and dyed to make hats. The vapors and the poisonous solution of the dye resulted in mercury poisoning to the makers which gave a rise to the term ‘mad as a hatter’.