Alum can be used to pre-treat paper and fabric before marbling to improve the transfer of the design as well as as a mordant for fabric dyeing with some natural dyes.
Usage instructions for marbling
For use when marbling on fabric dissolve ¼ cup of Alum in one gallon of water. When fully dissolved place the fabric into the solution. When the fabric is all wet remove from the solution and wring out the fabric – DO NOT RINSE. Leave the fabric to air dry fully before marbling. The fabric can be ironed before the marbling process if required.
For use when marbling paper dissolve ¼ cup of Alum in one quart of water. The solution can then be sprayed or sponged lightly onto the paper. Leave the paper to dry fully before marbling.