Blocking your swatch: step away from the pins
Updated: Mar 10, 2022

Are you pinning your swatches?
You’ve dutifully cast on and knit a generous swatch. You soak it, squeeze it, and lay it flat. Then, you pull out your pins.
Put the pins away!
Letting your swatch dry on its own will allow it to shift and settle into its accurate gauge. If you base your gauge on a stretched swatch, the first time you wash your sweater you may be unpleasantly surprised. If your pins have distorted your swatch gauge, your project may be either broader and shorter than anticipated - or narrower and longer. Pinning might also obscure something important about the fiber, like a bias twist, below.

Instead, put your swatch on a flat surface and gently pat it into shape. The soaking and squeezing process may have stretched the swatch some, so I like to pat it in a few directions to see how it lays the most naturally. Let your swatch dry - then let it sit for at least 12 more hours. Wool, especially, has a lot of bounce - giving the yarn that extra time to return to itself will create the most honest swatch.

Superwash yarn stretches when wet - a lot
If you've ever been unpleasantly surprised by what happened to your freshly washed superwash sweater, which now reaches your knees, this same principle may be at work.
A swatch is generally not very heavy, so there isn’t much distortion in a superwash swatch. Once you soak a whole sweater or piece of a garment, however, those sleeves can start to look like scarves as the water weight stretches the fabric. If you don't account for the stretching that takes place during soaking and squeezing, you will unnaturally distort your sweater.