In approaching the knitting of my next cardigan project, Every Last Yard, I had to swatch, naturally. I had talked with the designer, Amy Swenson (aka Indigirl) about achieving such a "Aran" gauge (16 stitches per 4 inches) with only worsted-weight yarn on 4.5mm needles. She told me to wash and block the swatch, then measure, to see if/how it stretched. Now, normally I don't wash and block my swatches (even though I likely should), but I thought it best to see how the yarn I was intending on using, The Sanguine Gryphon's Codex (single-ply, light worsted 52% BFL wool, 48% Silk), would knit, wash and block. Plus if the designer says so, then I best follow her instructions, no?
The Codex yarn is a fairly slender worsted, in my opinion, and 4.5mm needles seemed small for getting the necessary 16 stitches per 4 inches. So I started with 5.5mm needles, knit up my swatch, then soaked and pinned (blocked) it. It was 17 stitches pre-washing/blocking, and 14 after. Damn, too big. Am now seeing the importance in washing/blocking one's swatch...
I then went for the 4.5mm needles and knit up a second swatch. 22 stitches pre-washing/blocking and 19.5 after. Way too small. (Do you see where this is going?)
Sighing, I pulled out the 5mm needles and started a third swatch. I don't recall the pre-washing/blocking gauge, but post-washing/blocking came to 16.5. Close enough in my book. I won't block as aggressively in the finished piece anyway.
I haven't swatched so much for one project before, but I'm glad I did. I wanted to get it Just Right.
A second photo, to show more of the true sage-green of the yarn (the skinny pale gold swatch was from a sample skein of Codex that I received in a package from Sanguine Gryphon) :