With this column I begin a multipart series reviewing the manufacture, degradation and preservation of paper bank notes.
As with metal coinage, it is important that one understand the materials used to manufacture a paper note. Most paper money is printed on good-quality linen or cotton rag paper. Some emergency moneys and some scrip pieces are an exception. Both can be printed on poor quality paper and can be problematic as a result.
Rag paper is paper made literally from rags. Up until the mid-19th century, almost all paper in the Western world was made from this material. Paper makers would collect old, clean, cotton or linen rags for their product.
The scarcity of rags over the centuries is quite well known. In 1666 the English Parliament decreed that only wool could be used for burial shrouds, saving linen and cotton for paper makers.
The production process began by soaking the collected and sorted rags in water and allowing them to ferment for six to seven weeks to loosen the fibers. After fermentation the rags were washed and then macerated or “beaten” to further break down the material to form a pulp. The pulp was poured through a screen that caught the small cotton or linen fibers while the water ran through. Once dry, this mass of fibers formed a sheet of paper. Although this process is now mechanized, some artists and specialty paper mills still make fine papers in this manner.
After the paper was dried, it was usually sized so that it could be used for printing or writing. Sizing does not refer to cutting, but to the introduction of agents to stiffen the surface slightly. Sizing is important because it creates an even surface to receive the ink. New bank notes are crisp because of the sizing in the paper. Most papers were sized with different forms of animal glues (made from boiled animal hides). Modern papers are sized with a myriad of materials depending on the expected use.
It should be noted that color of early rag paper was variable. Essentially, the color of the rags determined the final color of the paper. The best quality paper was creamy in color, whereas poorer grades were mocha to gray in color. Rags were not bleached for papermaking until the early 19th century. In 1774, Dr. Karl Wilhelm Scheele discovered chlorine gas and the bleaching abilities of chlorine. By 1792, the first English patent for using chlorine to bleach paper was awarded. Chlorine bleach allowed paper makers to produce whiter and brighter products.
The demand for clean rags always surpassed the supply. As a result, early 19th century paper makers experimented with a wide variety of materials including bark and straw in the hopes of finding a cheaper widely available alternative. Eventually, in 1863, they discovered that paper could be made from ground wood.
Ground-wood paper was a major breakthrough, freeing paper makers from their dependence on linen and cotton rags. Newsprint is an example of ground-wood paper. Sadly, ground-wood paper is a classic example of what conservators refer to as “inherent vice.” It is inherently unstable. Over time it becomes acidic, causing itself to degrade.
I will continue this discussion next month.
Susan L. Maltby, Toronto, is a private conservation consultant, with an interest in numismatic preservation.