What is luster?
Oh, no! Meagan is at it again! Can we tackle an easier topic, like the cure for cancer or world peace, please? While the word luster brings to mind pearls and diamonds, it can be difficult to nail down exactly what luster means in regard to fiber. This is complicated by the fact that luster is most commonly used to describe mineralogy. Most of us can gather that it has something to do with shininess and light and that some fibers are shiny and some are not. This is a good place to start our exploration!
| Luster is… how light reflects off a surface Words we use to describe luster… shine, brilliance, glow, radiance, luminosity |
While that sounds like a simple explanation, this is where it gets complicated. Light may reflect off the surface layer or may pass through the top layer and reflect off the layers beneath, presenting a different reflective quality.
| Commercial production of rayon and wool use a full list of official descriptors applied to luster: 1. Clear 2. Bright 3. Semi-Dull 4. Semi-Matte 5. Dull 6. Matte 7. Extra Dull 8. Super Dull |
Luster in fiber is often expressed as a range from shiny to dull, with the most shiny and most dull fibers easily identified near the ends of the spectrum and all other fibers somewhere in the middle. Lincoln and Teeswater might be at one end while Southdown is at the other. However this doesn’t take into effect how the light is reflected. How would silk compare to Teeswater? Not all shiny is equal. For today, let’s stick to wool.
Luster in wool
The microscopic structure of wool is one of the primary factors in determining the luster of the fiber. For example, high-luster wools like Coopworth, Teeswater, and Wensleydale are fundamentally different from low-luster wools like Merino, Cormo, or Southdown. Beside crimp structure, the main difference between these wools is the size of the scales that make up the surface of the fiber. High-luster wools have larger scales which cover more surface area. When light hits these larger scales, more light is reflected in one direction, creating more shine. Low-luster wools have smaller scales. This causes the light to diffuse in different directions, so less light will be directed toward the eye.
I mentioned crimp. Crimp can also impact how lustrous a fiber appears. A higher crimp wool redirects light in many more directions than a low crimp wool, resulting in a more matte appearance.
What suppresses luster? How it is spun!
It is important to understand how luster changes when spun. In the most basic sense, worsted spinning makes use of a short forward draw and a combed fiber preparation to create a smooth, dense yarn. Woolen spinning makes use of a long draw and a carded fiber preparation, usually rolags, to create a light, fuzzy, warm yarn.
A worsted yarn will always be more lustrous than a woolen yarn of the same type of fiber. In a worsted yarn, we smooth down the fibers, helping them to align more parallel to each other. When the fibers are aligned, light tends to reflect in the same direction, making the fiber appear more lustrous. More light reaches our eyes. On the other hand, a woolen yarn has fibers crossing and going in all different directions. The different angles and bends of the individual fibers redirect light in all different directions, resulting in a duller appearance.
In addition to woolen and worsted techniques, the amount of twist you add can impact luster as well! The more twist added, the less luster. Why? The more bumps there are, the more light is diffused in different directions.
Try this!
Luster is impacted by how we spin. If we take a fairly lustrous fiber, how will the luster present in the finished yarn if we spin it with a worsted method vs a woolen method?
You will need:
- A sample of lustrous wool, like Teeswater, Wensleydale, or Cotswold
- A spindle or spinning wheel
- Spin a sample of yarn using a woolen long draw.
- Spin a second sample of yarn using a short forward draw.
- Compare the two samples.
- Which one appears more lustrous?
- What words would you use to describe the luster of each?
- Can you think of a reason you might try to reduce the luster of a high-luster fiber by spinning it woolen?
- What other tricks could you try to increase or decrease the luster of your samples?
Challenge!
Take the same fiber and wet spin it. How does this sample reflect light when compared to the first two?
Tell us in the comments!
