This is the method that is commonly used in tie dyeing, but that’s not all it’s good for! This is a good starting point to create a bunch of different variations of dye methods! 
Supplies:
- Synthrapol (a professional detergent)
- Dust mask
- Gloves
- Bucket
- Soda ash
- Water
- Funnel
- Procion dye
- Urea
- Bottles for dye
- 100% cotton fabric or clothing
1. Prewash your item in hot water with Synthrapol. This removes any sizing, oils or dirt that can prevent dye from sticking.
2. Using your mask and gloves, prepare the soda ash solution in the bucket. Add 1 cup of soda ash per gallon of warm water. Allow to fully dissolve. Helpful tip: 1 gallon can dye up to 12 adult XL tees or only a couple sweatshirts.
3. Soak for at least 15 minutes.
4. Still using your mask and gloves, prepare your dyes. Using the funnel to add 1 Tbsp urea per 1 cup of warm water into the bottles and mix until dissolved. Add in the dye. Use more or less dye depending on how deep you want the color. I use dyes from Dharma Trading, which recommend approximately 2 tsp per cup of urea/water solution (dyes indicated with * or ** need 4 or 8 tsp respectively). Allow the dye to fully dissolve to prevent weird color spots on your fabric. Helpful tip: 1 damp t-shirt can absorb about ½ cup of prepared dye
5. Apply dye in your preferred method. Try out some different techniques!
6. After dying, keep moist in a plastic bag for 24 hours. See here to see why 24 hours is recommended.
7. Rinse under cold running water (still tied if applicable) until the water runs clear. Untie if necessary and run under warm water until the water runs clear again.
8. To fully remove all excess dye soak the fabric in a bath of the hottest water possible (boiling water is okay for cotton) for about an hour (careful not to burn yourself!). Drain and give the fabric a quick rinse. Repeat until the soak water is mostly clear (a slight tinge is okay). This may take 3-4 times.
9. Fill your washing machine on hot cycle with 1/8 to 1/4 cup of Synthrapol. Add up to 8 adult shirts at a time and wash through a full load. Dry as normal.
What if my washing machine isn’t connected to hot water? And does it matter if the machine is HE or not?
You’ll be getting most of the excess dye out in step 8 if you’re using very hot water, so just make sure you keep changing out the water until the it is mostly clear. As long as you have gotten the excess dye out this way, washing in hot with a machine isn’t absolutely necessary. Most people just recommend doing step 7, rinsing, and step 9, washing in a machine in hot water. In this case it would be necessary to wash in a machine on hot, and since HE machines use less water, they’re actually not as good at… Read more »
Okay! That is awesome! That hot water wash was discouraging me from trying.
Is the synthrapol necessary? If I don’t do step 9?
If you are using fabric that’s prepared for dyeing (PFD) you could skip the initial wash, but otherwise you do want to wash your item before dyeing. If you can’t get synthrapol for the prewash you can try regular laundry detergent or dish soap (if you’re washing by hand). You just want something that has as few additives as possible and absolutely do not use fabric softener as these will cause uneven dyeing.
Soap isn’t strictly necessary at the end but you could add a little to the water bath in step 8.