Potassium Aluminum Sulfate
Alum is used to pretreat fabric or paper before marbling to ensure that designs transfer clearly. It is also used as a mordant with some natural dyes.
For Fabric Marbling:
Dissolve 2 teaspoons/10 grams of Alum in 1 gal/3.79 L of warm water. Immerse fabric in solution until wet, wring out (do not rinse) and let air dry. Fabric will be ready to marble when dry, and it may be ironed before marbling.
For Paper Marbling:
Dissolve 2 teaspoons/10 grams of Alum in 1 qt/0.95 L of water. Spray or sponge on the solution to lightly coat the paper. Let dry completely before marbling.
CAUTION: Keep dyes, paints and chemicals away from children. Avoid unnecessary contact. Do not ingest.