Contemplate

These 2 shirts are dyed with a layer of polyester fleece backing, to bulk the thin shirt fabric. Lay it flat first.

Stuff the shirt into a bin and make sure it's snug enough to keep the peaks upright. Good drainage is a must.

A second shirt is folded and set up in the same way. One shirt is left to melt at room temp. The other is set up with a space heater speeding up the melting.

Which side of the shirt should face up? I can never remember what looks the best. Probably face down is best. haha.

Both of these shirts were set up on an incline, with mega blocks holding up one end of the metal bin.

This is the result of the faster melt speed. I think it caused the dye to move through the shirt faster than it could react to the fabric.

Make tall scrunches and squish them together. Taller will make longer flowing lines.

Sprinkle powdered procion dye over the ice. I no longer suggest adding more soda ash on with the dye.

This shirt has a more even result in color saturation, with a longer melt time. Neither is wrong, but I do prefer the slower melt.