Ice dyeing is a technique for creating random patterning on fabrics (or fibres and yarns!). The dyeing method below uses Procion MX dyes on cotton fabric.  
Ice Dyeing with Procion MX Dyes – George Weil
Procion MX Cold Water Dyes for Cellulose
Tie-dyeing Cotton Onesies using Jacquard Procion MX Dyes
Procion MX Cold Water Dyes for Cellulose
Ice Dyeing with Procion MX Dyes – George Weil
Which Dye for Which Fibres? – George Weil
Fibrecrafts Procion MX Dyes for Cotton & Linen
Ice Dyeing with Procion MX Dyes – George Weil
Tie-dyeing Cotton Onesies using Jacquard Procion MX Dyes
Dyes & Dyeing – Page 4 – George Weil