Hand dyeing threads for quilting and embroidery is really quite simple. Here are a few tips if you fancy having a go yourself.
(My thread is mercerised cotton and I’m dyeing it with Procion MX fibre reactive dye).
I think threads are best dyed with a low water immersion technique so I’m using shallow trays (cat litter ones work fine, new of course!). Smaller quantities could be dyes in plastic pots, you could re-use ice-cream tubs for instance.

For variegated thread colours, you don’t want the skein swimming in dye, it’ll just end up one murky colour. The first layer in the tray ought to be fabric, this’ll soak up the spare dye giving you loads of control about where the colours flow and the bonus is you’ll get gorgeous fabric that coordinates perfectly with the threads!
Make sure the fabric is clean, any finish has been removed and most importantly is compatible with the dyes you’re using. If you’re using Procion MX like me then you’ll want cotton or linen. Don’t bother with polycotton it’ll be horrible as none of the poly fibres will accept the dye. Soak the fabric in soda and salt solution (I’ll put my recipe a the end) for a few minutes making sure it’s all fully saturated. Lightly wring it out (wearing gloves) allowing the excess solution to go back into the bucket. You can re-use this.
Arrange the fabric into the tray. Aim for a nice even layer, but experiment with folding and crumpling for different effects. I pack it fairly tightly in a crumpled way.
Pour on the first colour. I recommend using the lightest, brightest colour first so with the colours I favour that usually means yellow. Pour on enough dye, don’t skimp, you’ll only get pale and pasty results. Now carefully flip the entire layer of fabric taking care not to flick any dye up the walls or yourself.
Arrange the thread skeins on top. These too have been soaking in the soda bucket and have been gently wrung out. I arrange them in rows like neat soldiers so I can see where I’m putting the dye on each one. At this stage, press them down with a gloved hand. As you can see in the top photo, they’ll take on a bit of that first colour of dye.

Now comes the fun part! Add the others colours of dye you want to use. I mix each colour in a plastic jug or pot so I can pour it on easily and not bother with a spoon. Apply the colour carefully to target specific areas and think about colour theory! Too much of everything and you’ll just get brown. For rainbow effects try to apply one colour at one end of the skein, something else in the middle and something else at the other end.
Add enough dye! Peep in amongst the skeins and look for white bits. Press with your fingers to push them into the dye. It shouldn’t be pooling, there should be just enough for everything to be well saturated.
