Fuller’s earth is a catchall term for a number of absorptive clays. It gets its name from the original use to which it was put -“fulling” – or removing oil, dirt, and odour from sheep’s wool.
Sheep are naturally protected from the weather because their sebaceous glands produce lanolin, a fat that covers their fibrous wool coat and skin. The problem is that raw lanolin, and other nasty things on sheep make a greasy, foul smelling mixture that must be removed from the wool if you want to be socially acceptable when wearing it.
In times past, two “detergents” commonly were used for fulling wool – fuller’s earth and stale urine. There is nothing like scrubbing your woolies in urine and clay to get them clean, I always say! Who comes up with these ideas?
Anyway, fullers filled huge vats with stinking stale urine and fuller’s earth, put wool cloth into the vats, and stomped on it until it was clean. After the wool cloth was sufficiently stomped it was rinsed in clean water. Then, the wet cloth was stretched on wooden frames called tenters, so that it could dry and straighten its weave without shrinking or creasing. The cloth was hooked to the tenter frame with tenter hooks, hence the origin of the phrase, “on tenter hooks” (meaning in a state of anxiety). {{image2-A:R-w:300}}
Strange as it may seem, the process worked. To help understand why, take a look at the label on your shampoo bottle. My shampoo contains ammonium lauryl sulfate, ammonium laureth sulfate, and ammonium chloride.
The urine in the fuller’s brew produces similar ammonium salts. These ammonium salts are surfactants (surface active agents), which are molecules that have a water-loving (hydrophilic) end and a water-fearing (hydrophobic) end. As the surfactant molecules bop around in the fuller’s brew, they come in contact with lanolin and dirt on the wool.
The hydrophobic end of the surfactant molecule sticks to that stuff, while the hydrophilic end maintains a strong interaction between itself and the adjacent water molecules. Eventually, so many surfactant molecules gather on the lanolin and dirt that they surround it and roll it up into globules. The end result is that the oily globules are lifted off the wool—they have been emulsified.
The fuller’s earth brought its own capabilities to the party. Some fuller’s earth has strong cation exchange capabilities, which may have helped soften the water, thus assisting the surfactants with their job. Fuller’s earths are good at both absorbing (like a sponge) and adsorbing (sort of like static electricity) certain substances and can lock up some of the nasty stuff floating around in the soup. In addition, some fuller’s earths have strong bleaching properties and are good at whitening the wool.
Today, fuller’s earth has much more refined uses. It can absorb oil, grease, and pet waste. It is a binding agent for foundary sands, a carrier for fertilisers and pesticides; and clarifies animal, vegetable, and mineral oils. The movie industry uses fuller’s earth to make sets look old and dusty, and beauticians use it to make faces look young and healthy.
A final note. Back in the 1940s, fuller’s earth was an integral ingredient in Minipoo, a dry powder substitute for shampoo. The Minipoo ad claimed: “No soap … no rinsing … no drying. Removes oil, dirt … odours.”
Life would have been much easier for the fullers if only the sheep had regularly dusted with Minipoo.