To start, make the starch by mixing potato dextrin and water into a thickened paste, directions on package. Set this aside or refrigerate until ready to use (can be refrigerated for a limited time0.
Use a piece of insulation board - around 1/2 to 3/4 inch thick and pin the fabric down (right side up) very tight @ every 1/2 to 3/4 of an inch. As the paste is applied and allowed to dry, it shrinks and cracks.
Place the pins at an angle with the top of the pin going outward and the bottom of the pin going in, which stretches the fabric more tightly.
Next, apply the paste. It was an experiment of sorts to see how thick to apply it; the thicker areas were more crackled. A thin layer allows you to see the fabric underneath; a thicker layer will conceal the fabric. Allow the paste to dry thoroughly overnight. You will see it starting to crack as it dries.
Next, apply the color to "fill" in the cracked areas. Use a thickened dye (preferred) or a fabric paint such as Set a Color. A dye will leave the fabric softer, a paint will alter the hand of the fabric. I use a procion dye (mixed with soda ash) and thickened with sodium alginate. Next photo is fabric covered with potato dextrin solution.
To avoid extensive pinning, which is time consuming, you can also hoop it as seen in the picture below.
And now to apply the dye; it should be thick enough to conceal the fabric underneath.
Cover with plastic to keep the fabric moist and the dyes reacting. Let sit overnight.
Remove the dye by first rinsing in a laundry tub first to remove excess dye. Next, wash in cold water, then hot water with synthrapol. The water should run clear. It's a subtle and interesting look.