Hand dyeing is an art, and as such, variations are unavoidable. That's really what gives it beauty. Sometimes, though, things come out really so far off from what was expected that something must have gone wrong. Here I've listed a few common problems and what I've found can be the cause.
My fabrics came out much lighter than I expected.
Did you remember to add the right amount of soda ash to the chemical water? Too much or too little can interfere with the dye setting.
Did you let the fabric sit in the dye solution long enough? Although the dye starts to bond immediately, you need to let it sit at least four hours for best color.
Are you using PFD fabric? It may seem like "natural" muslin would be fine, and sometimes it is. But sometimes it won't take the dye correctly. Try switching to a PFD.
How fresh is your dye? Most texts say the Procion dyes have a shelf life of a year. I've used dyes longer than that, but I've seen them start to go bad after they've been on my shelf for a couple of years. If you are buying dye from one of the larger suppliers, it should be fresh. If it's from the local craft store, ask them how long they've had it. If they aren't sure, and it looks like it's been there a while, pass on it.
There are little "bursts" of intense color on my fabric.
You may have spilled some of the dry dye powder on the fabric and didn't notice, or you didn't dissolve all the dye before dyeing the fabric. Your choices are to overdye it, or live with it. Some hand dyers do this on purpose, as a special effect.
I did a two color run, but it came out looking like lighter and lighter shades of one color.
The "missing" color didn't take for some reason. If you're sure you mixed the chemical water correctly for that color, check the freshness of that dye.
The colored areas look fine, but there are big white areas on my fabric
Did you prepare your fabric correctly? Any sizing or oils left in the fabric can interfere with dyeing.
How tightly did you crumple the fabric? If it's crumpled too tightly, the dye can't get to the interior areas, and those will remain white. Again, sometimes that's an effect you want. If you don't like the result, you can always dye it a second time.