PFD means fabric that is Prepared For Dyeing. Ideally, that means you could just take it right off the bolt and dye it, but I never assume. I prepare about 10 yards at a time, and keep it ready for dyeing inspiration to strike.
Why use PFD? Why not use any old white muslin? White muslins often have "optical whiteners" to make them look bright and appealing. Unfortunately, that takes up the microscopic space where the dye molecule wants to be, so the fabric doesn't accept the dye well. That doesn't mean you can't use it, but you won't get the vibrant "wow" colors you can with PFD fabrics.
Like most hand dyers, I use Procion MX fiber reactive dye. Isn't that a mouthful! It's sort of a fancy way of saying this is not the dye you buy in the grocery store. There are a few very important differences. One is that this is a cold water dye -- no boiling or microwaving. This makes the Procion MX fiber reactive dye very easy to use. Also, the color is permanent, and stays vivid for quite a long time. Basically, this is the same dye the clothing manufacturers use when making your cotton clothing, so you know the colors will hold up well.
These dyes only work on natural fabrics. Essentially, that means cotton and rayon, and silk if you use a slightly different method than I'm giving here. Polyester, nylon, and other synthetics will take the dye only weakly if at all.
In dyeing, the "primary" colors are considered to be Fuscia, Lemon Yellow, and Turquoise. Mixing these three colors will give you intense, clean colors. For purposes of these lessons, I'll assume that's what you're using. But try other primaries, too. (Golden Yellow, Royal Blue and Fire Red make a great combination. Or try Golden Yellow, Navy, and Maroon.) Brown and black can be used to "tone" and "shade" colors.
Later on, you'll want to add the secondaries (orange, green and purple), and even some tertiaries (all the colors with hyphenated names, like red-orange, yellow-green, etc.) to your dye stash. Sure, you can make a wonderful purple from red and blue. But the color you get has a different quality because the red and blue dyes are taken up at different rates, giving you halos of color. Personally, I think this is the prettiest part of hand dyeing, but sometimes it's not what you want. But by the time you're buying those dyes, you'll be on your second or third bolt of cloth anyway. :-o
A resist is almost anything that keeps dye off an area of fabric, or stops it from spreading past a certain spot on the fabric. The resist may be something that is later removed (like wax in batiks), or it maybe something that becomes part of the design. Each resist has a little different personality, so plan on doing some experimenting with whatever resist you use before you start on your masterpiece.
Soda ash changes the pH of your dye solution, which is what makes the color permanent without heat setting. Do not use washing soda like you find in the grocery store, as this has ingredients which will keep the dye from setting.
Some people report good prices on soda ash at pool supply houses. Even with freight, I've found getting it from Dharma is still cheaper for me, so double check prices before assuming.
In my not so humble opinion, every quilter should have this on hand. Synthrapol is basically an excellent detergent, which does two things for us as hand dyers. First, when preparing fabric to be dyed, it gets any greases or oils left from manufacturing and shipping out. It also removes the sizing some manufacturers add (why they do it on PFD fabric is beyond me!). Unlike regular detergent, Synthrapol doesn't leave any residue on the fabric that might interfere with dye take-up.
After dyeing, Synthrapol grabs all the dye particles that aren't firmly attached to the fabric fibers, and gets them into solution in the washer. That way the excess dye goes down the drain, and doesn't end up staining your next project.
Synthrapol acts the same way for purchased fabrics (assuming you prewash). It cleans the fabric, removes sizing and surface chemicals, and gets out all the excess dye that can cause problems.
Urea simply helps fabric stay moist longer, giving it more time to absorb the dye. Use it for cup dyeing, painting (and other special effects) with dye, and screen printing with dye. Because baggie dyeing seals in all the moisture, you don't need urea for baggie dyeing.
If you'reusing urea, add 1/4 cup of urea to each quart of chemical water.