I wrote this up for someone who was asking about dyeing... I overdyed more this weekend, so I'm including some pictures along with it. I am still learning as I go, but here's what I did (specific to painting yarn):
I skeined up the yarn using a niddy noddy, lightly tied it with some scrap wool yarn, and soaked it in a splash of Synthrapol and water for about an hour. I did not move the yarn in the water at all. (note: on later batches, I soaked in vinegar/water mixture)
When I couldn't wait anymore, I pulled out my face mask and gloves, and mixed up Jacquard acid dyes with vinegar/water in squirt bottles (however, I have used this technique with KoolAid in plastic cups with sponge paintbrushes before). I mixed the powders over damp papertowels to pick up any stray dye.
I gently let the water run out of the sink and squeezed the excess out, and laid it out on the plastic wrap. I used the squirt bottles to place the dye with spaces in between each color so it would not muddy when the dyes traveled.
I used less dye than I expected, figuring it was easier to add more dye than to try to remove extra dye. I squished the dye in place with my hands to make sure the yarn was saturated, and checked to make sure the bottom side was covered in dye. (Thank goodness for rubber gloves, I did not dye my hands this time!)
I mopped the extra dye off the plastic wrap with papertowels, tucked in the ends and sides of the plastic wrap and rolled it up, placed into a pyrex dish used just for dyeing, and microwaved it in two minute intervals (two minutes microwaved, two minutes resting, two minutes microwaved).
By then, the dye had exhausted, so I set it aside to let it come up to room temperature (about an hour, just to be safe). Then I rinsed it gently in room temperature water, and let it soak for a few minutes in water with two glugs of vinegar in it. I rinsed once more to remove the vinegar smell, squeezed out the excess water gently, and let it airdry overnight.
I also made some red sock yarn, using an immersion method.