Some more dye experiments from the past day...
Pic 1: a quick color chart of the dyes I got that worked well. I made most of these before I realized that small differences in dye bath temperature make such a big difference in how fast and how hard the dye takes. Most of these were made by taking the dye to a boil, taking it off the heat, and dropping in the keycaps, but I wasn't being particularly careful to keep the temps and timing strict. Still... they're not *too* far off.
I also tried out the iDye Poly Black; I don't have any keycaps from that run because I did it last weekend, it went badly, and I didn't save the results. The iDye colors really need to be filtered before use, else the results end up swirled and speckled due to a nasty, greasy residue, I think left over from the self-dissolving dye pouch. In any case, once filtered, these dyes work great. The black came out a sort of hunter green before darkening to black with longer soaking time.
Other colors that don't appear either sucked (Rit Pearl Gray-- did nothing) or I didn't have it to try.
Pic 2: experimentation with dye concentration using the iDye Poly green. I made several dye runs, each time cutting the dye concentration to 1/4 or 1/2 the previous run (mixture concentration listed to the left). These tests account for evaporation; I measured volumes and replaced lost water each run, but used the same dye. I also did this one before realizing temperature was so important; notice the 1:4 L line is actually darker than the higher concentration 1:1 line above it. Noticing that is what spurred me to run the temperature experiment (and then start being much more careful about temperature).
The conventional wisdom I've read is 'make your dye mixture as concentrated as possible'. I've begun to think this is wrong. Notice that the last row on this pic is equivalent to one packet of dye in 64 liters of water. The dye bath at that point was a translucent middling green. There was no problem with dye uptake, and the light green made by soaking in a lower concentration for longer is more even than the green made by soaking in a high concentration for a few seconds.
My best guess is that the dyeing is a simple exponential diffusion. Eventually the concentration of dye in the plastic will reach equilibrium with the dye in the water. Riding the very steep part of that diffusion curve will give a less even dye job than letting things run longer at a slower pace--- this last part is a guess. I've not run a controlled experiment of that lovely little theory, so it could be completely bogus.
Pic 3: same experiment as above but using the Rit Black. The Rit dye is either much less concentrated than the iDye, or it doesn't take up as well (or both). The Rit Black is also prone to unnevenness before getting to a solid black, and intermediate stages are beige/brown/dark brown.
One thing I didn't expect with the black: as I kept cutting the concetration, the color appeared to get warmer (more reddish). Perhaps this is just an illusion caused by differential uptake of the different dye colors, eg, the red takes longer to diffuse such that the longer a cap soaks, the redder it gets and you can't tell in the earlier runs because the resulting colors from longer soaks are too dark to see it. Or, maybe the dye hue really was shifting after being at near boiling for several hours. Dunno, maybe I should run another test... ;-)
Pic 4: a newer shot of the temperature test keycaps from earlier-- I wanted to retake it paying more attention to exposure and white balance, and so it would match the rest of the pics
