Last week I bought two sets of Sulky 12wt cotton to try, having heard a lot of praise for them, and having enjoyed using one of their 12wt “Blendables” (variegated colours) in the Butterfly Wreath. Some of them (with a few others acquired since) were bought with a third version of the Hope rainbow in mind; the set of muted pinks and greens has no immediate purpose, but I just found the colour combination irresistible!

“12wt”, or “12 weight”, by the way, refers to the thickness of the thread, or more accurately to its length: it is defined as the number of kilometres of thread in a kilo. So 12 kilometres of 12wt thread and 40 kilometres of a 40wt thread both weigh 1 kilo. This means that the higher the number, the thinner the thread; 12wt is roughly equal to two strands of standed cotton.

Before the Sulky threads arrived I took the opportunity to compare the thickness of my Blendables 12wt with a Weeks Dye Works perle #12 (they happen to be stored together as I got them both – plus a few others – when looking for just the right variegated green), mostly to compare thicknesses as you would expect the 12 in perle #12 to stand for its weight as well.

But as I put them down on white paper together I noticed something unexpected: Sulky blendables is a Z-twist! I’d never noticed this before because the Butterfly Wreath doesn’t use it for a stitch that shows up the difference clearly, like stem stitch.

I remembered that some years ago I purchased a few spools of another brand of 12wt cotton at the Knitting & Stitching Show. I dug out a spool of Wonderfil and yes, that’s a Z-twist too. But the WDW overdyed perle is, predictably enough, an S-twist like most other hand embroidery threads.

And that last bit (“hand embroidery threads”) turns out to be the pertinent fact in this twisty surprise. Some research online brought up an interesting page on the website of thread manufacturer Yli, which says that “A thread with a Z-twist, or left twist, is engineered specifically for the sewing machine. The action of the sewing process tends to increase the twist of a Z-twisted thread, but can actually untwist a thread with S-twist, or right twist.” We live and learn! The threads are still perfectly usable for hand embroidery – I’ll just have to remember to work my stem stitch as outline stitch. Fortunately I don’t think many of the other stitches in the Hope design are affected; other than stem stitch just the whipping, probably. I wrote about the effect of the whipping direction in an earlier FoF, finding that I liked a Z-direction whip with an S-twist thread (that is to say the whipping and the thread twist go in opposite directions), so here I’ll have to do the whipping in the S-direction. Oh well, think of it as brain training.

Incidentally, coming back to the relative thickness of all these threads labelled as a size 12 – the Sulky thread is clearly thinner than the other two. Could it be because of a difference in twist? Sulky’s appears to be longer/less tight than either the WDW perle or the Wonderfil cotton. Must do a bit more research!