Tuesday, November 04, 2014

Indigo and woad or Isatis tinctoria

Lustrous wool fibers mostly present a hydrophobic surface.   In a few places, there are polar bonds where water droplets can attach or dye molecules can bond.  If those places are bonded to a (blue) dye molecule then those previously hydrophilic areas also become hydrophobic, and there is no place whatsoever for a water droplet to rest, so it will be easily shaken off.  (Yes, I anthropomorphize hydrogen bonds.  ) 

The bottom line is that blue wool sweaters ARE more water repellent.  This can be affected by any of the modern mill treatments that chemically alter the surface of the wool fibers -- most notably the treatments that make wools machine washable, but also aggressive carbonization to remove VM, and processes to stretch and thin the wool fibers.

This tells us that woad likely has such wide distribution in the North Atlantic because it was carried from island to island.  It was carried because it was vital to making serviceable clothing for seamen. Woad (and indigo) made wool more water repellent.  (And woad was a treatment for ulcers. NB the prevalence of ulcers on seamen.) This tells us that the ecru Arans were either made for tourists or were intended to be worn under an oil skin.  Since woad is found on the Aran Islands, then at sometime in the (long) past, it was brought to the islands, and likely used to make blue woolens.  (And, you also find Urtica dioca, there because nettle fiber was preferred for fishing line and nets.)  

This also explains why soap (not detergent) is the better washing aid for woolens that will be worn in the rain or fog.  Soap will tend to make (natural fiber) wool more water repellent.  If your garment care instructions indicate that it is to be "dry cleaned" then it was not intended to be worn in foul weather.  Real fishermen, who need to preserve the fine blue color of their woolens will wash them in stale urine.  (If the object was properly dyed, additional acid will not act as a mordant.  If the object was not properly dyed, then the dye should be set with acid before the fisherman puts it on.) Sadly, real fishermen must rely on real spinners, real dyers, and real knitters, rather than on mills run by bean counters.

A woolen washed in soap, with a drop of baby oil in the rinse water does not need lanolin. Lanolin smells sheepy when it gets wet.  Lanolin attracts moths.  Lanolin gets sticky and attracts/holds dirt. "Wool spun in the grease" and "oiled wool" are myths that stand in the way of warm woolens worn in foul weather.

Anyone that wants to assert that blue sweaters are not warmer than other colors, should be eager to discuss Lewis Acids/Bases and the structure of wool fibers in excruciating detail. 




Anonymous said...

First, congratulations on learning to spell "woad." It probably helps when you're doing google research.

Second, neither of those articles provide any proof of your assertion that blue-colored wool is any warmer than any other dyed wool. (I minored in chemistry and am fairly knowledgeable about physics and am able to read and understand scientific papers.) Your original claim was that your "scientific" test proved that garments made with blue dyed yarn were warmer than any other color, including black. There's nothing in either article that has anything to do with your supposition and nothing that supports your claim. The first paper explains Lewis's theory of acid and base ions (as opposed to other acid/base ionic theories); nothing about why the color blue is, as you claim, "warmer." The second paper is about the effects of the process of shrink-proofing wool; nothing to do with dyeing and in particular the use of the color blue.

You don't need to make up pseudo-scientific explanations of why blue was a popular color for ganseys. I'm quite sure the wool processors and users in the 17th century in Britain didn't consider (or know) any scientifically proven physical properties of woad when they chose to use it to dye wool yarn. They chose it because it was PRACTICAL. Light colored sheep wool shows dirt really fast. Dark colored sheep wool doesn't. Dark colored wool is scarcer than light colored thus more expensive. How to make white darker? Dye it with a dark color. Black dye was unavailable until the mid 1800’s. Woad was cheap and easier than any other color. Hence, blue ganseys. Keep It Simple, Stupid.

Lastly, I have no idea how a scientist could think one drop of baby oil (no matter your definition of a drop) could sufficiently coat 1/2 a kilo or more of wool to waterproof it.
Pat Brunner

Avery said...

Your wild extrapolating is highly entertaining. I truly wanted to believe that perhaps you were writing this as some form of satire, but I realize you're serious. I bet gansey wearing sailors would be highly amused that you think blue sweaters are warmer.

Stacey said...

I don't think you have it quite right.
From How Stuff Works:
Lik­e we said, wool can soak up a lot of moisture without feeling wet. This makes wool a hygroscopic insulator. The crimp in the wool fiber forces each strand to butt against each other, as opposed to lining up side by side or laying down flat together. This keeps the tiny air pockets intact, acting as little insulators -- the key to being able to keep you both warm and cool. Air has the ability to move heat by convection -- in other words, by moving and circulating. Through convection, air can transport heat from one place to another. When air is contained in very small pockets, it can't circulate easily, so heat is retained. Same goes for cold. Think Styrofoam cooler -- the Styrofoam's tiny pockets of air act as an insulator for heat or cold (depending on what's inside the cooler). The same concept goes for wool.
There's also some science at work here. Wool fibers are made up of cortical cells, and these cells are wrapped in cuticle. This scaly outer layer is then covered by yet another layer, the epicuticle -- a filmy skin that helps to repel moisture. What's more, the epicuticle also helps out in high humidity because it has tiny pores that draw in the moisture vapor to the center of the fiber where it's absorbed by a chemical process. The hydrogen bond of water, H2O, is actually broken, creating a chemical reaction with the wool fiber molecules to generate heat when it has taken on a lot of moisture. But because the air pockets allow moisture to evaporate from your skin, you won't overheat when you sweat.
The combination of the fiber's natural crimp and the chemical and physical processes that take place when wool meets moisture make it the best all-season natural insulator on Earth. It actually absorbs water from both your skin and the atmosphere around you to create a dry and warm environment where it counts -- against your body. So the next time you pass a herd of sheep standing around in the pouring rain looking dopey, remember the complexity of their protective coat.