My process for dyeing dolly parts: Prep is everything!
This isn't exactly instructions, but if you've been doing dyeing and it's not working, this is what I do.
Sand: To dye resin smoothly, use a stupidly high grit wet-sandpaper and an N95
or higher rated mask for you, and sand the part thoroughly to really
smooth it out a little. (Don't let the dust get anywhere. It must not be
inhaled by anything with fleshy lungs, so do this bit outside and make sure you
clean up! Use water to keep the dust contained, then dispose of it
Scrub: Then scrub the part with a Magic Eraser or melamine sponge
equivalent. Then wash it with a drop of clear dish soap and water, making
absolutely sure to get any oils from your fingers off it. After that,
handle it only by the back and edges.
Dip: Put a bit of string or wire in a loop through the hole/s in the part to dip it into your dyepot. Make sure the string is long
enough so the rising steam from the boiling dye doesn't hurt your hands.
Use a small pot that isn't enameled, teflon-coated or aluminum; steel
is best. Do this somewhere with daylight lighting so you can
compare the part to the resin you're trying to match. If you're doing a whole doll in one color, start with an easy-to-clean part like a forearm, get it the shade you want, then match each part afterward to that. I like to open all
my kitchen windows to get proper light for seeing color by. Bring water to simmering boil, add dye, stir with a
cheap wooden spoon, not a metal one. It has to be boiling, but a
rolling boil is too hot. Then you can dip the part in. Make notes of the precise amounts of dye you use, and the amount of water you started the pot with. You may need this info later.
Match: Go slowly- you can always add more color but taking color away is
really, really annoying. Rinse the part in warm water to see what color
you've actually gotten to, and to remove any excess dye.
Smoothing: Check it as you get close to the color you want, and if it's blotchy,
take it out, scrub blotchy areas with magic eraser. Re-dip it again.
Repeat as needed until you get the color you want. Rinse, allow to dry
well and totally before using MSC to seal. If it isn't bone dry, the MSC will cloud.
"My first part has the wrong color/ is dyed too dark!" - Scrub it clean with a Magic Eraser and some WinsorNewton Brush Cleaner, and wash it with the dish soap again, rise totally clean of soap, then try again.
"My Tan dye is dyeing the doll blue!" (Or other unexpected color)- The chemistry has gone wrong. It's possible your pot has a coating, or is made of aluminum, or sometimes you can even just get a bad bottle of Rit. Scrub the part and try again, with some changes accordingly.
"My dyed doll has darker streaks on the sides of their parts, like where seam lines go." - Yep, that's where seams were. This is the nature of dolls cast in resin, and can't be totally gotten rid of. If the streaks are really dark, see the Smoothing step, and try that, but they won't be totally invisible on some dolls no matter what you do. Blushing can help.
"My doll has streaky spots..." - Do the Smoothing step over again, possibly including a bit of scrubbing with WN on the part where streaks are. residue of old sealant, finger oils or WN must all be scrubbed off then washed carefully off. Clean resin streaks much less.
"When I wiped a faceup attempt off my dyed doll, the dye color got lighter." - Yes, this can happen, as you tend to remove some dye with the faceup. This is why we made the notes about the dye and water mix we dyed it with. You can just replicate your dye recipe, wash your head/face really well, and re-dye it, or you can just blush the new faceup to account for lost color. The same goes for Body Blushing.