This is how I do it. Get an old plastic dish basin or tub, spread some netting over the top and down the sides and tape it with masking tape to hold securely. Do not stretch it over too tight or too loose, it has to hold the pieces and the ice over the basin for 24 hours. I dye small pieces and use one color combo in one batch. I only had enough soda ash to do a couple batches, so I used a substitute which worked just fine. The fabrics I've used are 100% cotton PFD (prepared for dyeing) solid, white on white, muslin, silk, and velvet. Soak your pieces in the soda ash for 20 minutes and wring out but don't rinse it out. I do this in a big bucket. Twist, tie or just scrunch up the pieces any way you want. Place them close together on top of the netting. Gently place the ice over all the fabric pieces. Using a plastic spoon, sprinkle the dye powder over the ice. Do this in a draft free area, protected from children and pets. Also follow all health and safety rules like wearing a mask and rubber gloves.
I only use 2-3 colors to dye with. As the ice melts the colors will bleed together in places and if you just sprinkle the dye onto the ice, you will have spots that have been missed making some nice patterns.
This is a silk scarf that was ice-dyed using only 3 colors.
These pieces were created using 2 colors and the fabric was tied and twisted which created the channels and circular patterns.
Some of these pieces would look great as a whole cloth quilt. I ended up doing 5 separate batches and have at least 5 yards of dyed fabric.
Once you give it a try, you'll want to experiment more to see what your results will be. Have a sew-full day... :o)