Can I make up my waxed fabric for batik, let harden, put in a plastic baggie and pour dye over it for a not-too-wasteful bath of dye?
I don't see any reason why not. You may want to keep it moving, just to get a nice even color.
How do I know if it's a small enough to call low or larger for high? I think I sort of understand the difference in terms of how will look, the low is more of a mottled, crumpled look, but the high is more of an even shade through the garment?
depends on how you fold it, but generally, yes.
Will placing the garment in a baggie crush the wax too much?
I don't think so, but again, it depends on your desired effect. If you want the least cracking, get a vat. and if you want lots of cracks, crumple away. I suppose it would also depend on the size of the piece and of the bag and how much wax is on the fabric.
If I take a garment and dye a section with full strength dye, then add water to the dye and dye the section next to that, then add water and dye the section next to that... etc... will I end up with a garment with a graduated lightening of the color? If I don't use any ties and am somewhat generous with the dye so it bleeds, will it be more gradual and less like discrete stripes?
yes. You can also do a gradation by just dipping one end in dark dye, and letting the dye bleed upward into the fabric. it's smaller.... but it works for me.
I've got foam q-tips and tjan-whatever those tool things are called. Is there any sort of requirements for paintbrushes that are safe to use with melted wax?
Foam q-tips I would discourage, just because plastics tend to melt. Brushes should be natural hair, because acrylis bristles warp and get quite wonky if not molten. I suppose it would depend on the melting temperature of your wax, but they don't vary THAT much. you can use whatever you like, it's your project!
What's the most efficient way to work with a lot of small items in different colors? I'd been thinking of making up master bottles and using small bottles to make up one item's worth of mixed up color at a time? Is it more efficient to wax up everything, let it harden, then soda ash whatever needs to be ashed, then let that dry, and dye as I find time to do a few pieces here and there? I've got three small children -- spare time is hit and miss.
I would mix up a bunch of dyes ahead of time, not every color, but the basics, blue yellow red. and mix the secondary colors from those when you need them. Procion dyes have a long shelf life, you can reuse dye a few times over. Of course each time it gets more diluted, but it's still a good thing to do.
YUP! I hope I helped at all any