Rhuallen asks…Hair dye washes out quickly. Wool is hair. Wool dye is very durable. Why isn’t the same technology used for human hair dye?
The Beauty Brains respond:
Like wool, hair is dead. But unlike wool, human hair is still attached to something alive! The technologies used to to dye wool are simply not safe for application to humans.
Cleaning process
According to Ranching with Sheep (sounds like the sequel to Running with Wolves but I’m pretty sure that’s a coincidence) the wool has to be washed thoroughly with a good detergent in order to remove all traces of oils, which can interfere with dye absorption. So no moisturizing shampoos allowed!
Wool must be mordanted
Wool, like hair, is resistant to dye (the cuticle prevents large molecules from being absorbed.) So, to prepare the wool it must first go through a process called “mordanting” which opens up the fibers to allow the dye to penetrate better.
Mordanting uses some chemicals which are relatively harmless (like alum) and others which may present hazards (like chrome and tin.) But regardless of the chemicals involved, the process is a killer. It requires soaking wool in a solution of the mordant agent at 160F for almost an hour. Hey, I’m all for a long, hot shower but that’s ridiculous.
The coloring process
And if you think that’s bad wait until you see the coloring process! Some wool dying techniques use heat to accelerate the process and to help bind the color. Temperatures during these processes can reach as high as the boiling point of water. This is NOT very good for your skin. And to top it off, certain dyes require a strongly acidic environment (with pH as low as 1.8 which is achieved with sulfuric acid.)
The coloring chemicals
Because of the extreme processing described above, wool can be dyed with some fairly innocuous ingredients, like stains made from marigold flowers. But there are also some pretty nasty dye materials used on wool. For example, metal complex dyes are used which are based on transition metal ions such as chromium, cobalt, nickel and copper. These metals are not necessarily in a form that safe for application to humans. (Although they do provide a broad range of colors for wool dyes.) Acid and reactive dyes are also used for wool. In order to level the dye (i.e. make it absorb evenly) wool may be soaked in high concentrations of Glauber salt which is sodium sulfate. This is not something you would leave in contact with your skin for any extended period of time.
How hair dye works
Contrast the wool dying process with the hair dying process which only takes a few minutes, is done at room temperature, doesn’t require extreme pH, and involves chemicals which have been proven safe for human contact (although some have the potential for causing an allergenic reaction.)
The bottom line
It’s a clever question but unfortunately using the technology for dying sheep’s wool on humans is a baaaaaad idea. The process is not safe for us to use because of the chemistry and processing conditions involved.