Volume 1, Number 4
Oct 1988

The Coloring of Pulp in Alkaline Papermaking

There are a number of factors that a papermaker considers in the selection of a coloring system. Mainly, these relate to the intended use of the paper.¹ In this article I shall deal primarily with the factors of permanence and durability,² qualities that are paramount in our own work at Carriage House with paper for printing and for art.

When we started making paper by hand back in 1974, we had no preconceived ideas of how to color paper pulp. We began by utilizing the natural colors of the fibers that we pulped. Subsequently, to achieve further coloration, we used some readily obtainable fabric dyes.³ These yielded brilliant colors, but lacked the lightfastness necessary for our work.

By this time, we had become aware of the factors that contribute to the longevity of the paper itself, e.g., the type of fiber in the furnish, the method of fiber preparation and additives that can result in acidity or alkalinity.⁴ Therefore, when w Embarked upon the investigation of coloring systems, we had already been convinced of the importance of producing neutral or slightly alkaline papers. A coloring system would have to be in harmony with this.

We approached the paper research division of a major chemical firm⁵ that manufactures dyes and pigments, and asked for recommendation of a system that would yield a full palette of lightfast colorants compatible with alkaline papermaking. Immediately we were led astray, resulting in hundreds of tests with many different dyes, none of which proved suitable for our purposes. The basic problem was that the parameters of longevity⁶ are very different for the general paper industry than for us, who are making paper for books and art. It almost seemed that a colored paper was considered lightfast if it didn't change color within a couple of months of sitting on a shelf in a paper shop. Once we got the definitions straightened out with the technical representative of the chemical firm, we were able to develop a coloring system that met our goals.

There are two parts to a coloring system. The first is the selection of the actual coloring agents. The second is the method by which the colorants are attached to the substrate. The coloring agents that met our standards for longevity were all pigments (not dyes).⁷ Essentially, they are the same pigments that are used in the highest quality artists' oil paints, watercolor paint, or acrylics.⁸ We tested many dozens of pigments, making sample sheets of paper which were tested for lightfastness.⁹

The method for adhering the pigments to the pulp was another temporary stumbling block. A common way of retaining additives in paper pulp is by means of alum and rosin. This often results in an acidic paper. It was necessary for us, therefore, to select another kind of binder that would be effective in an alkaline system. After a great deal of experimentation, we settled on a particular type of retention agent,¹⁰ namely, a cationic fixative. The fixative is a polyamine, a synthetic polymer of high molecular weight, neutral in pH. It is used by the paper industry to provide retention of dyes, pigments and other fillers added to pulp. Finally, we worked out the actual method of application of the pigments and retention agent, in regard to order of addition, quantities to be used, and other procedural matters. We ended up with a specific set of directions for these procedures, which could yield intense hues, with very satisfactory retention of the pigment in the paper.

At the finish of our research and experimentation, we realized that we had developed a very simple method of coloring paper pulp, one that was extremely well suited to the needs of hand papermakers. There was nothing new that %we invented or discovered. We simply recognized our own needs in term of permanence and durability of paper, and determined what was available commercially that would suit these needs. There was one final matter that needed resolution, namely that the materials necessary for our pigment system were distributed only in quantities suitable for regular commercial paper mills. No one was repacking these supplies in amounts feasible for small hand papermaking operations. We had already encountered a similar situation with other supplies we use, mainly paper pulp. Therefore, we had set up a supplies business, buying bales of fibers and pulps, and reselling them in small quantities. So we simply added pigments and retention agent to our list of resale items.

In conclusion, I wish to point out that there is no problem in coloring paper pulp in an alkaline papermaking system. Both the technology and the materials are readily available.

End Notes:

1. Major factors are aesthetics, permanence, availability, ease of application, cost, and safety.

From: Color for the Hand Papermaker, by Elaine Koretsky. Brookline, Mass.: Carriage House Press, 1983.

2. These are term that industry uses to describe the longevity of paper. Durability refers to the condition in which usage is taken into account; the word implies resistance to normal 'swear and tear." Permanence is resistance to the effects of time, brought about either by internal factors in the composition of the paper or by external factors in the environment, without any actual physical usage of the paper.

3. We used "all-purpose" dyes, such as RIT, Cushing, Putname, and also fiber-reactive dyes, such as Procion.

4. Suggested reading on this subject:

John C. William , "Chemistry of the Deacidification of Paper," Bulletin of the American Group - The International Institute for Conservation, 12(l): 16-32, 1971.

Paper Permanence: Preserving the Written Word. Boston: S.D. Warren Co. (1982?).

5. Sandoz Chemical Co., Charlotte, NC.

6. Our colored papers were tested according to the Blue Wool Standard or by a Fade-Ometer. The Blue Wool Standard is used by the American Society for Testing and Materials. We were searching for colorants which that Society would rate as excellent in terms of lightfastness. For complete information on this subject, see Color for the Hand Papermaker, pgs. 18-21.

7. Pigments and dyes are the general categories of coloring agents. Dyes are substances that are soluble, usually in water, and actually penetrate the structure of the fiber, the dye becoming attached to the cellulose molecules of the pulp because of chemical reaction and/ or physical attraction. A dye is substantive to the material it is coloring, that is, it has an affinity to the material and will become part of it without the use of a binder. Pigments are insoluble, finely ground particles of coloring matter which are deposited physically on the fiber, and must be held onto it by mechanical means. The pigment has no affinity to the material it is coloring, and requires the use of a binder.

8. These three types of paints are combinations of pure pigment plus the additives which produce an oil paint, vs. watercolor vs. acrylic. They already contain binders, so that they adhere directly to an appropriate substrate, e.g., canvas or paper. The pigments we use in coloring pulp are pure pigment dispersed in water; they contain no binding element.

9. See Note 6. After extensive testing, we decided upon 11 individual pigments, which not only suited our requirement of permanency, but gave us a fine range of color. The 11 pigments are:

The names of these pigments, as listed, are the Colour Index names, by which these pigments are designated world-wide. The Colour Index is published jointly by the American Association of Textile Chemists and Colorists and the Society of Dyers and Colourists in England.

10. The retention agent is one manufactured by the Sandoz Co. The exact formula is proprietary.