Fill the large plastic tub or pail three-fourths full of warm water. Mix in one cup of soda ash for every 10 pounds of dry cotton fabric or clothing into the water. Stir and let the soda ash dissolve.
Add the cotton fabric into the soda ash-water solution and soak it for 24 hours. Soda ash is a potassium-based salt that enhances the dyes. The soaking time gives the fabric time to absorb the salt, allowing brighter and more vibrant color from the Procion dyes.
Mix the Procion dyes in squirt bottles. Put the funnel in the top and spoon out the measured amounts of dye. Different colors require different ratios of water to dye. Black requires the most amount of dye to water, typically a 3 to 1 or 2 to 1 ration, depending on how dark you wish the black to be. If unsure of the ratio for your desired color, use the Procion mixing chart.
Close the squirt bottle top and shake until no visible dye chunks remain. If you wish to dye using a brush, fill bowls with the dye fluid and use sponge brushes to apply to the fabric. If you wish to vat dye, transfer the dye into a large tub.
Rinse and wring the cotton fabric or clothing from the soda ash water. Apply the dye with squirt bottles or sponge brushes, or in the case of vat dyeing, by dipping into the dye solution in a large tub.
Lay out the dyed fabrics or clothing and cover with plastic sheets for 12 to 24 hours, depending on how bright you want the colors.
Fill the washing machine with hot water and set to a double hot rinse. Add three tablespoons of Synthrapol brand detergent for every 10 pounds of fabric or clothing. Once the machine is full, drop the dyed clothing into the machine and let it run through the full cycle and extra rinse. Synthrapol neutralizes dyes as they come off the fabric, keeping the dyes colors in the fabric the original colors.
Dry the fabric as directed by the care label.