What determines shrinkage?

Andrew, over at weave4fun describes a curious case of "differential shrinkage".

I told him it has happened to me, too - but as I can't post pictures on his blog, the illustration comes here, instead.

This is a ... lap rug? ruana? - piece of woollen cloth. It has the same yarn in both warp and weft, in several colours/shades.
The yarn comes from an old industrial stash, is woollen-spun and has a grist slightly finer than 6/2 Nm (which is the Swedish "standard" yarn for making blankets).

The longest side is 160 cm, the shortest is 144. The widest end is 47 cm, the narrowest is 42.

- the phenomenon is true for all yarns from this same source, so whenever I want a gradated weave I have to be extremely careful when wet-finishing...

The only explanation I can think of is that the light-coloured yarns have been bleached, and (because of harsher treatment) therefore shrinks less.

I would be very interested to hear other theories!

(It has happened to me with a couple of other yarns, too. And it has always been the dark shades that shrunk most.)


humblebumble said...

now, i can't be certain with all yarns, but my understanding is that all yarns are bleached prior to dyeing. I suspect that coloured yarns have undergone more wet-treatment than the white yarns. It's worth noting that the yarns I was talking about on my side, the white ones were both white and off-white.

I'll look out my notes later on tonight and see if i can confirm this. But this is an issue I'll be taking up with my tutors when I get back to college.

Also, related, something I noticed last year when I was weaving a sampler in 16-shaft double cloth, with one layer black and the other of various colours. The black yarns would break. A lot, but not the coloured ones. This was wool as it goes. I mentioned it to my tutor and she said that often when the dying goes wrong and they get the wrong shade they just go and redye it as black, so as not to waste yarn. Therefore it's weaker as it's been dyed twice.

Interesting, I wonder myself if it's sold as seconds? Anyway, after that I just started replacing the broken black ends with cotton, as the weave technician assured me noone would notice

Kerstin på Spinnhuset said...

I'll have to think about this - however, note that I'm saying *dark*, not *black*.
The shorter edge of the ...blanket is the dark(er) red; the narrower part is the dark blue.
Well, again: I don't *know*, I'm just guessing.

humblebumble said...

i looked it up. my notes say bleaching is only carried out if:

1 - the product is to be sold as "white"
2 - a pale shade is being dyed

India said...

Vi fick ett annorlunda problem med ett ulltyg i tuskafts bindning som efter att ha blivit vått fick kypertränder och såg helt enkelt skryngkligt ut. Ullen levde helt enkelt sitt eget liv och ränderna var ohjälpligt fast i tyget. Man blir ibland lite överraskad.

Kerstin på Spinnhuset said...

India, jag tror att vad ni råkade ut för är vad de engelsktalande kallar "tracking" (som i "spår").
Det kan hända i vilka material som helst, om man har relativt hårdsnodda garner i relativt gles inställning.
Man kan ibland pressa bort märkena, men de tenderar att komma tillbaka nästa gång man tvättar.
(- somliga jobbar hårt på att *få* så'na märken...)