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.)