Step 1: Materials
n.b. The pool or hardware stores sell soda ash as sodium carbonate. Any pH upper will do! you want around pH 10 or 11 to fix "fiber reactive dye".
n.b. Arm&Hammer has a natural washing soda, sodium carbonate decahydrate, that contains water in addition to sodium carbonate, so use maybe 3 times as much.
Cold Water Fabric Dye : powder. $4 per little bottle (3 quarters (<--US currency) tall). 1 tablespoonish per shirt bag, will dye a second shirt, too. at least. I use Procion MX.
Some salt (tablespoon ish)
Some ziplock bags
Some gloves or plastic bags with rubber bands
A shirt or any kind of natural (cotton) fabric to dye.