Stir each color dough separately. Knead each color, adding flour as necessary,
until it is bread dough consistency, only a little stiffer.
Roll light dough on floured surface into a 1/2-inch thick rectangle. Roll the
dark dough to the same dimensions. Spritz the top of the light dough with water.
Lay dark dough on top. Fold tightly from the long edge like a jellyroll.
Wrap in plastic wrap and freeze for 1 hour.
Cut 1/2-inch thick.
Bake at 350 degrees F for 1 hour, then turn oven off, crack
oven door and leave in until very hard, about 8 hours.