The subject of take-up and shrinkage has come up a number of times lately, specifically in relation to yarn substitution. My general thoughts on yarn substitution can be found here.
Take-up is how much the yarn rebounds after it is removed from the tension on the loom, and shrinkage is how much it shrinks after wet finishing.
Conventional wisdom goes something like this: cotton takes up and shrinks about 10%, wool 15%, and highly elastic yarns 20%.
Synthetics generally take up about 10%, but it depends how they are manufactured. You have to think about their qualities in relation to the natural fibers. Are they manufactured to be more like cotton or more like wool.
The kind of fiber, fiber prep, and the structure can also make a difference. Sometimes unmercerized cotton takes up more than mercerized, and some wools, such as longwools, and some camelids, take-up less than the average wool figure of 15%.
If you know a little bit about fiber types, then you can extrapolate from the pattern what the take-up and shrinkage is likely to be. If the pattern uses a longwool and you are using a wool with more elasticity, then you are likely to experience a higher percentage of take-up. (I provide the highlights of fiber behavior as it relate to weaving in my book A Weaver’s Guide to Yarn.)
How to Determine Take-Up in a Published Pattern
You can determine the take-up in width and length by looking at the project’s specifications in the pattern. Compare the width in the rigid-heddle reed with the finished width and the woven length vs. finished length to calculate a percentage of difference.
Calculating Take-Up in Width
Say the project lists the width in the rigid-heddle reed as 23” and a finished width of 21”. To determine the take-up and shrinkage in width, divide the finished width by the width in the reed and you will get .912, which is the total amount of width you would get from a 23” wide warp in the project’s yarn type. Resulting in about about 9% take-up.
Calculating Take-Up in Length
Then take a look at the woven length of the fabric vs. the final finished fabric. For example, if the woven width is 60” and the final finished fabric is 53”. Divide the finished fabric length by the woven length. That gives you a take-up and shrinkage percentage of about 13%. It is common to see more take-up in length than width, although it can depend on the structure.
Evaluating the Results
Take an average of the width and length take-up and get an overall percentage. In the example above, my average take-up would be 11% (9 + 13 = 22 ÷ 2 = 11). Compare this figure to the conventional wisdom about take-up. In this case, the percentage is a little low for wool and about average for cotton. Then think about the yarn you want to use and how it fits into this spectrum.
One area that often trips folks up is the relative elasticity of one yarn compared to another. A yarn that is the same size, yarn construction, and general fiber type (wool, cotton, rayon, acrylic) can behave differently in the fabric based on the yarn’s elasticity. This most notably shows up in take-up. Have you put on the exact same-sized warp and woven the same amount of fabric the pattern calls for, yet the fabric comes up short when you take it off the loom? Many weavers attribute it to their mis-measurements, but it could be due to elasticity.
Certain breed types or yarn construction have more elasticity or rebound than others. For instance, here are two yarns that appear similar on paper. Each one is shown relaxed (outer) and under tension (inner). They are similarly-sized, worsted-spun, plied, wool yarns. However, the yarn on the left has less elasticity than the one on the right. This is created by both the specific wool type, a wool cross vs. a breed-specific Targee wool, and the yarn construction or amount of twist and plies each yarn has.
This is a very subjective answer, but I think of highly elastic yarns as ones that act more like a rubber band than a piece of string. If you stretch out the yarn, does it want to snap back in place readily like a rubber band, or does it relax more like a piece of string? If it acts more like a rubber band then I’d consider it to have high elasticity and treat it as such, adding more warp length and width if needed.
Modifying a Pattern Based on Elasticity
When adding more length and width, take into account the fact that you already have some take-up built into the pattern. If the pattern take-up is 15% and your yarn takes up 20%, add an additional 5% to the warp length and add a couple of extra ends to the width. I tend to add less to the overall width because, like in our example, take-up tends to happen more in length than width.
With highly elastic yarns, it is even more important to use an open beat so the yarn has room to rebound when off the loom. It may seem very open, but the fabric will have a better hand if you resist overpacking. An added bonus is you have to weave fewer picks with an open beat.
Here is an example of a classic superwash sock yarn that has a lot of elasticity: on the loom (left), off the loom (middle), and after finishing (right). The final fabric is spaced nicely, but if you overpacked it on the loom the yarns may look a little crowded and that would affect your drape.
Yarn and weaving are endlessly fascinating to me. In these “geeking out” posts, I’m digging into the nuances of the craft, but don’t let it scare you away from taking your best guess and weave away. If things didn’t quite go as planned, take a look through the blog posts and see if there isn’t a bit of geekery to take with you to the next project.