This was my second time dyeing a bag from a craft store -- it's really quick and easy, I recommend it to everyone!
Step 1: Needed Materials
*Something to dye
*Dye (both times I've used Rit brand -- it works wonderfully and it's the only dye I can vouch for)
The best place to do this is in a bathtub. The first time I dyed something I used a shower and water went everywhere. In a bathtub, the mess is contained and cleanup is easy.
WARNING: There is a chance you will dye the drain and/or surrounding area the same color as the dye, so make sure you can mess up the area you are working on. If this does happen, the sooner you clean up the dye the better. (Tilex worked, since I didn't have bleach handy.) However, porous surfaces will hold the dye -- I found this out the hard way, when not even pure bleach took the blue out.
Step 2: Preparing the Dye
First and foremost, rinse the bucket. Use water to wash out any particles of dust or anything similar -- what is left behind will most certainly be dyed and later poured down the drain (which sadly makes for some entertainment later on if you are as easily amused as I am).
Pour hot water in the bucket, as warm as you can stand sticking your hand in. Fill the bucket so that whatever you plan on dyeing will be submerged in the liquid.
Also, if you are doing this in a bathtub, I highly suggest filling the tub with enough water to cover the bottom. This makes cleanup easier later on, as no dye has time to dry in your tub.
Pour in the package of dye. Stir until the powder is fully dissolved. DO NOT use your hands unless you'd like to dye your hands. As far as how much dye to use, both times I used only one box of dye when the directions suggested two and both times the color came out beautifully. The largest bag (the one seen in the pictures) was 18x13xsomething -- so consider the size of the item you're dyeing.
Step 3: Time to Dye!
Place the object to be dyed into the colored liquid. Use the stirrer to poke and prod the object, guaranteeing that the dye will get into every tiny crevice. Even once the object is fully coated with some amount of dye, DO NOT leave it alone. Stir and stir and stir until you're done dyeing the object.
Note: DO NOT stick your hands into the dye. Even a minimal amount of time in the dye will affect your skin. I stuck my hands into the dye to get the spoon, which I accidentally dropped in the dye, and my hands were a tad purple afterwards. After washing my hands twice, though, the dye went away.
How to tell when it's done:
Find a shade of the dye that you like and keep it in the dye a bit longer. You can't time it exactly, just realize you're going to place the object into water to stop the dyeing process and some of the dye will come off. If the dye isn't getting any darker, it is probably at its max absorption level and it won't change colors anymore. Even once it is rinsed off, it will probably end up that same color (why, I don't know -- that's just how this appears to work).
Step 4: Finishing Up and Clean Up
Once you have achieved a shade darker than you'd like, take the object out of the dye and rinse it with warm/hot water. You will have to do this until the water runs clear and no more dye is coming off (about 5 minutes-ish -- less for paler shades). As time goes by, slowly make the water cooler. The colder water sets the color.
When you are done rinsing the object, ring out the excess water. Place it somewhere to dry -- this process will take a long time (I'd give it +12 hours to be sure).
Now for clean up. If you are able, dilute the dye before pouring it down the drain. It will help whatever the dye stains be a lighter color, ie: easier to remove. Personally, I was not able to dilute the dye where it was, because the faucet was too low and the bucket too high. Instead, I just let warm water run while I poured it down the drain. I tried by best to pour it straight into the drain, but my stopper wouldn't allow that easily.
Once all the dye is down the drain, let the clear water run and clean up what you can as quickly as you can. Then, grab the bleach or Tilex and spray any area that appears to be dyed. If you do this quickly enough and the surface isn't porous, it should take away any remaining dye and return your shower/tub to normal.