Before being marbled, paper or material has to be coated with an Alum solution. Alum acts to fix colours and make the paper or material more receptive to the colour as well as also improving colour tone and lightfastness.
Directions are generally as follows:- 50g Alum to a pint and a half of water.
Mix 50g of Alum Crystals into a pint and a half of boiling water, stirring until the crystals are fully dissolved. Top up by adding a quarter of a pint of cool tap water to the measure. Once fully cooled, evenly sponge or brush the mixture onto the side to be marbled. Try not to allow the paper to get too wet. The paper can be used when slightly damp or completely dry.