It is important for knitters to understand the properties of wool fiber and how it is spun into yarn in order to choose and use it to its best effect. All animal fiber shares these same basic qualities, but sheep wool is the most common.
Wool Fiber
There are four factors that affect wool fiber: scales, fineness, staple length, and crimp.
- Scales: All animal fibers have scales. They help the fibers grab onto each other when spun, and also keep small spaces between the fibers that trap air and keep the yarn warm. Usually, the smaller the scales and the more there are the softer the fiber is.
- Fineness: The fiber diameter. The thinner the fiber, the softer it is. Younger animals tend to produce finer fiber, so lamb’s wool is prized for making yarn.
- Staple length: The length of each hair. Generally, shorter fibers are softer, but they tend to stick out of the yarn and pill so longer fibers are more durable.
- Crimp: The structure of the fiber may be straight, wavy, or curly. A tinier crimp spins into more bounce and warmth, but a greater crimp spins a denser and stronger yarn.
Different breeds of sheep have different properties of fiber, so manufacturers may blend different breeds together to get the best combination of strength, softness, resilience, and affordability.
Spinning Wool Fleece Into Yarn
The wool that is shorn off a sheep is called a fleece. This fleece has dirt, plant bits, and lanolin in it. Sheep secrete greasy lanolin in order to sheep their hair waterproof, and some breeds of sheep are so clean that their fleece can be spun “in the grease,” retaining the lanolin.
Before being spun, most wool fleece is put through a carding machine, which removes impurities from the wool and loosens and opens up the fibers so they spin into a better yarn. With woolen-spun yarn, the carded yarn is slightly twisted into strands of roving, which looks like a slightly smoother fleece. When the roving is spun, the fibers aren’t aligned so the finished yarn is loftier and warmer, but not as durable. With worsted-spun yarn, however, the fibers in the fleece are first combed so that they align, spinning into a smooth and durable yarn.
Fiber artists still spin yarn on spinning wheels or drop spindles, but most manufacturers use big machines. A single thread of yarn is called a ply, and manufacturers will usually twist several plies together to make the yarn stronger and able to withstand more abrasion.
Dying Wool Yarn
There are a variety of ways to dye yarn. When a yarn is dyed in the wool, that means that the fibers were dyed before being spun, which allows different colors to be subtly mixed into the yarn. Kettle dying and immersion dying are when the yarn is dipped into a big vat of dye and left to soak up the color.
The dye is applied to hand-painted yarn with a brush or roller. Some manufacturers, such as Knit Picks, sell yarns that have been deliberately left bare so that knitters can dye their own. And wool naturally comes in a variety of colors, so some manufacturers choose not to dye it at all.
Felting Wool and Superwash Wool
The scales on wool fiber are what cause felting. Hot water and agitation cause the fibers to swell and when the scales collapse on each other they stick together, forming the smooth look of felt. In order to prevent felting, wool must be gently hand-washed. The scales on superwash wool, however, have been glued down with a special resin so they won’t swell and felt, even if put in the washing machine. It’s important to pay attention to the yarn ball band for washing instructions.
Wool Allergies
Some people have an allergy or sensitivity to wool, and this can be caused by several factors. The scales of the ends of the fibers in the yarn may be scratching the skin. Lanolin, dyes, or other matter left in the yarn may also cause irritation. There are many different kinds of wool yarn, so look around to find one that won’t cause irritation.
Source:
- Parkes, Clara. The Knitter’s Book of Yarn: The Ultimate Guide to Choosing, Using, and Enjoying Yarn. New York: Potter Craft, 2007.
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