Tie-Dye Chemicals

Here is where safety is first in your work. While modern dyeing is less toxic overall than ever before, there are still risks associated with using concentrated dyes, caustics, and discharge agents. Here's a list of the major chemicals used in tie-dye and their safety concerns:

Dyes

RIT Dye: The liquid dye is safe, if not non-toxic. Use gloves to avoid staining your skin and direct exposure to the dye, and don't drink it. The powdered dye, like all powders, is more dangerous if only for the problems inherent in inhaling powder.
Fiber-reactive dyes: The liquid dyes are safer, but have shorter shelf life than the powders (months vs. years). Again, protect your hands to avoid contact with concentrated dye. The powdered dyes require extra attention to avoid inhalation, and you should wear a dust mask while weighing/measuring them.
OTHER dyes: You should review the MSDS for all dyes, and for each new dye be careful to review the safety guidelines for use. In general, avoid direct skin exposure to liquid solutions and use a dust mask when working with powders.

Caustics

Caustic potash (potassium carbonate): A strongly alkaline/basic chemical, take skin contact and inhalation precautions. In addition, take extra caution when pouring, or manipulating fabrics in these solutions, as droplets that get in your eyes can cause permanent damage. Protective safety goggles (vented, for use with caustics) are highly recommended.
LYe (sodium hydroxide): An even stronger base, this chemical requires all the above precautions with extra emphasis. A splash into the eyes can be blinding, contact with skin can rapidly cause burns. In addition, adding solid sodium hydroxide to water (and NEVER, NEVER, EVER add water to solid sodium hydroxide) leads to the liberation of a surprising amount of heat. I have made solutions in my laboratory that literally brought the water to the boiling point (and beyond), and this can happen rapidly around a clump of sodium hydroxide. When this happens, you create a bubble with a splash that puts concentrated lye in your face. Luckily, this caustic is not used in most tie-dyeing, with one of its few uses in dyeing found when dissovling natural indigo. Using synthetic, pre-reduced indigo allows you to use potash instead, which is much safer.

Discharge Agents

bleach: Bleach can be very dangerous, both from its own effects if splashed in the eyes or in prolonged contact with skin, and especially from the potential to liberate toxic, even fatal, amounts of poisonous chlorine gas. NEVER mix bleach with, well, much of anything but water. Acids (even weak ones like vinegar) and ammonia can lead to rapid release of chlorine gas, which is both toxic and can burn your lungs. It was used as a war gas in WWI, and many soldiers literally drowned from fluids released from damaged lung tissue. Don't be the guy who recreates old human evil and coincidently removes yourself from the gene pool prematurely. Even during simple discharge (without adding anything really stupid), chlorine gas is released. Rinse excess dye from the fabric if you are putting freshly-dyed fabric into bleach, which will reduce chlorine release. I do all my discharge work outside (regardless of the weather), and stay upwind. BE CAREFUL! Most instructions specify using a full cartridge respirator with acid gas cartridges - and I won't disagree.
Thiox (thiourea dioxide): Used as a direct discharge agent and in vat dyeing as a reducing agent. Safer than what it replaces (sodium hydrosulfite), it still has the potential to release a bunch of awful chemicals, including hydrogen cyanide and sulfur dioxide. However, the risk is relatively low, as shown in this assessment of a fiber arts studio that uses thiox regularly for discharge. Take all precautions, don't mix it with anything, but in general its a safer alternative to bleach in my hands. BE CAREFUL! Most instructions specify using a full cartridge respirator with acid gas cartridges - and I won't disagree.
anti-chlor: Used to neutralize chlorine bleach, it works wonderfully but you should take all the precautions for discharge agents, even though sodium bisulfite is considerably less likely to release toxic gases in the amounts used (a teaspoon or so per gallon). BE CAREFUL! Most instructions specify using a full cartridge respirator with acid gas cartridges - and I won't disagree.

Other

Urea: Generally quite safe, especially as the solid is pilled and exposure to dust is thus minimized. Wear gloves, don't eat it.
&etc.: Very little else used in tie-dye (as I've specified it) poses any significant chemical hazards, but be sure to read your instructions carefully and download the MSDS and read it.
Your eyes: Chemicals that are almost harmless to your skin, or even to ingest, can nevertheless do real damage to your eyes. Think jalapeño peppers. In general, all the chemicals that I use in tie-dye are unlikely to eat through my skin, kill me by their toxicity if used with a modicum of sense, or cause people downstream of me to get cancer. However, they can damage your sight. Be good, wear goggles and pay attention to how you pour and remove items from solutions. You have to be able to see to appreciate the colors.

RIT Dyes

Available in powder form or in pre-mixed liquid, RIT dyes can be used on fabric without preparation, or with the use of a mordant you can achieve greater color fastness. Here is a great site that spells out the use of alum as a mordant in dyeing using natural dyes, and another that introduces other mordants. In my experience RIT dyes behave like (and probably are, or at least like) natural dyes, and so applying a mordant is a great idea. Alum is accessible, you can buy ~1 oz styptic pencils in drug or grocery stores that are basically thumb-sized chunks of alum (potassium aluminum sulfate). Dissolve the alum (which you can also buy online, for example at PRO Chemical and Dye) at about 1 oz per gallon of hot water, then wet your fabric (to prevent streaking) and place in the mordant solution. Heat to near boiling, put the lid on, and let it sit for an hour or so. Remove your fabric from the bath, squeezing it out, and let it dry. Proceed with dyeing with RIT dyes.

Her's the rationale behind using a mordant. RIT dyes intercalate into (get between) the fibers of the thread in your fabric, and over time will wash out, resulting in fading. Mordants make the dyes less soluble in water, and so retard the washing out process. It's worth the preparation time to mordant when using RIT dyes.

Another aspect of using RIT dyes is applicable to fiber-reactive dyes as well: using agents that open up the fibers of the fabric to let the dye get access. For RIT dye baths, you use salt as the fiber-opening agent. With fiber-reactive dyes, urea is the agent of choice. To a certain degree they're interchangable, but urea is a better chaotropic (chaos creator).

Fiber-Reactive Dyes

These dyes are the most commonly used dyes for coloring cellulose fibers, and do so by a covalent bond between a side chain on the dye molecule and celluose. They are therefore "permanently" bonded to the fiber, which makes them very color fast. The chemistry is quite mature, and so the current crop of dyes are relatively safe, available in a wide variety of colors, and easy to use.

I buy my fiber-reactive dyes in powder form, as they have the longest shelf life and allow for a variety of uses, from making a bucket full of dye bath for immersion dyeing to sprinking the powder itself on fabric for a variable coloring effect. Here are some of the basic recipes for using fiber-reactive dyes in tie-dye:

Immersion Dyeing (for a pound of fabric=3 med t-shirts): Mix together 1-2 lb of salt, 5-7 tablespoons of caustic potash, and 1 teaspoon to 4 tablespoons of fiber-reactive dye powder in about two gallons of warm water. You can also use about a third as much urea instead of the salt. The ranges are about depth of color: if you want a really black black, you need 4 tbsp dye/pound fabric, and to get that to react you'll need 7 tbsp of sodium carbonate (caustic potash).
direct application: A day in advance, stir very well one tablespoon of alginate thickener (available as PRO Thick SH at PRO Chemical and Dye, my supplier) into a quart of water, and just leave that spoon in there. The next day you should have a thick gel, stir more and let it sit longer (covered) if it still has lumps. Dissolve 1 oz (7 tablespoons) of urea in water, and add a little water softener if your water is hard (Metaphos). Dissolve your dye in the urea solution at between 1 teaspoon and 3 tablespoons per cup, again depending on how strong/dark you want the color to be. Add thickener by the spoonful with stirring until the solution is substantially thicker than water but not like syrup.
direct application with steaming: Add 1 teaspoon of baking soda (sodium bicarbonate) per cup of prepared dye solution. Recognize that this will decrease the shelf life of your dye solution from a week or more (if refrigerated after use, and not used in the heat) without baking soda to about a day. I have also used the dye solution without baking soda for steaming using the same process as overnight dyeing without any ill effects. In other words, rather than applying dyes to fabric that's been "activated" by soaking in a solution of caustic potash, and then letting the dye react with the fabric overnight at room temperature, you can instead take this same fabric and steam it for 10-15 minutes to get the same effect. Or you can include baking soda in the dye solution, steam, and also get good color. The baking soda method is safer when dyeing with the young and less responsible.

[still working on the rest...]

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