Use of alum as a mordant for marbling has always been problematic because of its acidic nature - acids are associated with the deterioration of paper. Marbling without a mordant would be ideal, as was customary in the 18th and early 19th century, however modern papers, with their sizing and buffering, are not sufficiently absorbent to accept marbling paints.

Retention agents are compounds used in the papermaking industry to facilitate the binding of pigment to pulp. They rely on the ionic charge of the compound to create the attraction of the pigment to the fiber. I have been experimenting with these compounds and have found that when applied to the surface of paper, they will work as a mordant does, binding the pigment to the fiber.

The examples to the left were all made using Percol 292, a non-toxic cationic retention agent, instead of alum. Good color intensity can be achieved, although the papers have a slightly softer, less crisp appearance.

Application of the material is similar to alum: mixed in water, applied with a sponge and marbled in the damp or dry state (dry works better). The chief difference is that with this compound, the papers should be left on the size longer than with alum (about a minute or so) , and they should not be rinsed (which causes loss of paint). As in the eighteenth century, papers should just be left to drain and dry. This requires more attention to the balance of gall and paint - too concentrated a paint, particularly in the vein colors, will result in running of the paint and consequent staining of the paper (alum is more forgiving since you can just rinse the excess paint away) . Acrylic paints will work with this compound, and I have had no problem with any papers I have tested, so far (this material is also used to facilitate binding of calcium carbonate into the pulp). I have not been able to achieve good binding when using metallic paints.

The pH of the mixed solution is acidic, but it can easily be brought to a neutral or alkaline range without affecting the binding ability.

Percol 292 is manufactured by the CIBA company and it appears to me to be a good alternative to alum. It is quite cost effective, being equal to or less costly than alum per liter of solution. Additional tests are under way to determine its duration of potency in solution and preservation of potency in humid conditions (i.e. my house and basement in summer, which has made working with alum a real challenge). Additional directions and materials can be supplied upon request.