Some visitors might find being presented with a hat kept inside a strong plastic bag, emblazoned with a skull-and-crossbones and the word ‘TOXIC‘ in big authoritative letters, a little alarming. Perhaps they would be led to think that we had turned buccaneer, or perhaps that Captain Kidd‘s most cherished secret, the one that he took to his piratical grave, was a fondness for little poke bonnets. Visitors (and readers of blogs) of the less nervous, more chemically-aware, more pre-adolescent literary nature may have guessed by now that the reason for these bags is not to strike terror into merchantmens’ hearts, and nor is it to promote the interests of long-deceased marauders. What it does is tell us immediately is that this particular hat is impregnated with mercury.
The hat in question is a green poke bonnet dating from around 1816. It has a flat crown like a man’s top hat, and is made from beaver fur and adorned with ostrich feathers. Mercuric nitrate was used from the 17th century to cure the felts used in the construction of hats in a process known as ‘carroting’. Animal skins were immersed in a dilute solution of the compound, causing the fur and the pelt to separate and mat together. It was then dried in an oven causing the edges of the skin to turn orange (hence the bunnyfood reference). The skin could then be cut off in thin slices, consolidated, rolled into felt, then dyed and formed on a block to make a hat. Everyone will have heard the expression ‘as mad as a hatter’, which is a somewhat unkind phrase that originated from observations of the symptoms shown by hatters and mill-workers who had suffered prolonged exposure to mercury vapours. Indicators of mercury poisoning include uncontrollable twitching, confused speech and memory loss, and in particularly nasty cases, dementia and bleeding from the ears and mouth. Not nice, and also not subject to legislature until the mid-20th century.
Clearly we would all prefer to avoid the “hatter’s shakes”, and so a number of our hats are kept safely sealed, which allows us to still show them to our visitors if they’re requested.