The Incalculability of Wool.

I've been washing wool - and since I buy the wool from my suppliers, and sell it on after washing, sorting, and fluffing it up, I need to make sure to do the maths so my prices are okay. And I can tell you... wool maths is special. Also, it tends to make me grumpy, due to all this specialness. Want to share some of the grumpiness? Here you go.

Let's start with the basic inbuilt fudge factor that wool has. This lovely fibre can take up a lot of water before feeling moist, and while this is a glorious thing when you are wearing wool garments or sweating into them is a nasty thing when you are trying to weigh it. I try to make sure my wool is dry, and the weather is not humid, when I am weighing wool or portioning it out - but sometimes, there is no choice, so you have to estimate how much moisture is in the fibre.

So even clean wool can have weight differences due to different levels of humidity in the air. When you have raw wool, though, there's even more fudge factor.

One of the things the raw wool contains (apart from vegetable matter, which in the best case should not be relevant for weight at all) is lanolin. Then there's sheep sweat. In the bits that are usually removed, there can also be feces and urine. And there's also dirt, sticking nicely to the lanolin that coats the fibres.

So when you are buying a raw fleece, you are paying per kilo of fleece - and you might get a much, much lower yield out of your purchase, weight-wise, if things are unfavourable. For instance, if you buy a very dry skirted fleece (all the really dirty bits removed) with no vegetable matter, little lanolin and very little dirt, you can end up with a washed fleece that is about 15 or 20% lighter than the raw one. If, on the other hand, you pay for a fleece that still has a good bit of humidity inside, contains a lot of lanolin and a lot of dirt and has not been skirted fully, you can end up with a lot more loss in weight - up to 50%. That's half your raw fleece weight in washed fibre... which, if you have been counting on a specific amount of fibre to work with, can make for a nasty surprise indeed.

Just the amount of dirt and lanolin alone, by the way, can account for a lot - I've had a well-skirted fleece of about 3.8 kilo lose 1.3 kg of dirt and lanolin through washing; that's almost a third of the raw fleece weight.

Which means if you are buying raw wool, check it out thoroughly: Has it been skirted? Is there a lot of lanolin and dirt trapped between the fibres? Is it dry weather (cool temperatures are always less humid than warm ones) or is it humid? Count on a weight loss of at least 25% from raw fleece to washed fibre to avoid nasty surprises, and remember there will be some more loss when you are prepping the fibre for spinning or felting. When in doubt, do as usual when buying yarn or fibre for a project: add a generous amount on top, as a safety margin.

Wool maths. Grrr.