Bergdala Spinnhus

On differential shrinkage, and a tubular selvage

By "differential shrinkage" we often mean what happens when we combine shrinking and non-shrinking yarns in one woven piece. We often think that we can predict the results.
Sometimes that is correct. Sometimes it turns out that there are a good many more parameters than that...

For some time I have been making bumpy shawls using warp and weft stripes of a shinking yarn (wool) between wider warp and weft stripes of a non-shrinking yarn (cotton and/or linen and/or silk).
When I first started doing them, I experimented with different structures, different wool yarns, different widths of the shrinking stripes, and different finishing methods.

differential shrinkage
This is what I found:
  • weave structure is both more and less important than I thought:
    • plain weave, where wool crosses cotton, did not shrink at all - even with very open plain weave
    • ordinary 2/2 twill yields the same result as did more complicated structures (I experimented with double-sided 1/3&3/1 twills) - so, no need to complicate structures for the sake of it
  • different (makes of) wool yarns give different results, all other parameters being alike
  • wet finishing by hand is far too time-consuming for production. It was also difficult to apply the same amount of "work" to all parts of the items
  • so - machine finishing it was. It turns out that:
    • different washing machine programs give different results - but also: different washing machines (using the "same" program) give different results. This means that, to get consistent, predictable results, you have to make several samples and KEEP NOTES!
    • if all shrinking is done during washing, especially linen and silk can feel papery after drying - and it is difficult to press or iron the shawl
    • therefore it is a good idea to use a gentler washing machine program, wait until the shawl is nearly dry - and then put it in the dryer for the final shrinking and drying. And... you guessed it: first make samples, and KEEP NOTES!
    • (also remember to keep the loads more or less the same - doubling the load MAY cause more shrinkage!)
wavy selvages
When there was a wool stripe at the selvedge, that stripe often shrunk less than the inner stripes. A slightly wider outer stripe seemed to shrink more than a narrower, but it was still often longer.

To begin with, I did not find this a problem - the whole shawl was bumpy and wavy anyway, so why worry?

This is the original draft I used:
1:st draft
While still not seeing it as a problem, I wanted to investigate the phenomenon. The edge stripe acted as if there were more interlacements in it, compared to the inner stripes. This was, technically, not true. Except... the weft turned around the very outer yarn. Could it be this turn that trapped the wool yarn, preventing it from shrinking?

So... what would happen if I tried a tubular edge? After some experiments, I have come to use this draft instead:

draft for tubular selvage
(Green warp is wool - the different green colours are ONLY a way to make the reading of the structure easier! White warp is the non-shrinking cotton, linen, silk...
Dark green weft is wool, light green is the non-shrinking yarn - the first eight picks have different colours ONLY as a way to make the reading of the structure easier!)

If you examine the draft, you can see that the outer 8 warp ends form double layers in plain weave. Be careful NOT to tighten the weft too much - it may look sleazy, but the wet finishing and shrinkage will remedy that.

This threading gives a much more consistent shrinking of all the stripes.
tubular edge after fulling
So... how much shrinkage is "right"?

That is, as so often, a matter of personal taste.
Myself, I want the bumps to look obvoiusly intentional (as opposed to an "oops - it shrunk, I will try to press it flat" look), my preference is that the shrinkage is about 35-40%. If the shrinkage is over 45% the shrunken stripes get too thick, in my opinion.

... but the selvage don't have to be shrinking. Here is another idea:

For this shawl I used a darkish blue cotton for one "ruffle", a lightish blue for the other and a purple wool for the shrinking stripe.
The weft was a midrange blue cotton.

ruffles draft
See more "shrunk" ideas here.
ruffled shawl

  © Kerstin Fröberg 2010