Why Pre-Wash Fabric?

Pretty red print quilting cotton--it can be a trouble maker, despite its innocent appearances . . .
My "Patchwork by Machine" beginner class starts at the Neighbourhood House tonight. I'm looking forward to it. There are eight students. Several of the students are on the Neighbourhood House staff in one capacity or another and lately every time I drop in there I'm greeted with a sample of fabric, or a choice of colours, or a dilemma about fabric choices, or just all round general excitement about the class. It's been quite a build up and since the Neighbourhood House is all about developing community, I guess we're ahead already, even before the class begins.

Yesterday's dilemma came in the form of a little jar of water. The point is, the water was a reddish colour and it shouldn't have been. L had done the right thing and pre-washed her gorgeous red fabric ready for the class. Red water was the result. Not a good start! Especially since her contrast fabric is a lovely delicate red on white print. I gave her a bit of my "hi-tech wash off" to soak the fabric in. Hopefully that will get rid of any loose dye that's still hanging around.

I put instructions to pre-wash and iron fabric for the quilting class on the list students were given when they enrolled. I did that for three good reasons--aren't there always three good reasons!

1. To wash out any excess dye and sizing. Excess dye can stain other fabrics in the project when it is washed. That's not nice. Sizing is the starchy stuff that manufacturers use to finish their fabrics for presentation in the shop. That's fine, but sometimes lots of sizing disguises a really poor quality fabric. I'd rather know about that before I put a lot of effort into sewing it up.
2. Shrinkage--even good quality cottons can have up to 3% shrinkage on washing. 3% doesn't sound like much, but that's 3 cm out of every metre. Also different fabrics shrink by different amounts. If they shrink after they're sewn together that causes puckering and distortion. Better to get the shrinkage out of the way before starting the project.
3. General misbehaviour:) Some fabrics don't behave well when they are washed. Maybe the grain-line is distorted, or it's a fabric that just frays a lot, or the texture of the fabric changes . . . whatever the problem is I want to know about it ahead of time. Then I can either adjust my project or choose a different fabric.

As for ironing, it's not my favourite activity, but it makes my cutting more accurate, and that makes it worthwhile.