Poster collecting today is for both fun and profit. Yet, the poster you thought was going to increase in value year after year has suddenly turned yellow after only three months and is now worthless. What happened? What could have been done to prevent the yellowing? This article will discuss how paper is made. What materials are best suited for long term storage and the guidelines for proper preservation.

How Paper is Made

Paper generally has plant fibers that have been reduced to a pulp, suspended in water and then matted into sheets. The fibers in turn consist largely of cellulose, a strong, lightweight and somewhat durable material; cotton is an example of almost pure cellulose fiber. Although cotton and other kinds of fiber have been used in paper making over the years, most paper products today are made from wood pulp.

Wood pulps come in two basic varieties: ground wood and chemical wood. In the first process, whole logs are shredded and mechanically beaten. In the second, the fibers are prepared by digesting wood chips in chemical cookers. Because ground wood is the cheaper of the two, it is the primary component in such inexpensive papers as newsprint, which is used in many newspapers, comic books and paper backs. Chemically purified pulps are used in more expensive applications, such as stationery and some magazines and hardcover books.

Since ground wood pulp is made from whole wood fiber, the resulting paper does not consist of pure cellulose. As much as one-third of its content may consist of non-cellulose materials such as lignin, a complex woody acid. In chemical pulps, however, the lignin and other impurities are removed during the cooking process.

Deterioration of paper

The primary clauses of paper deterioration are oxidation and acid hydrolysis. Oxidation attacks cellulose molecules with oxygen from the air, causing darkening and increased acidity. In addition, the lignin in ground wood paper breaks down quickly under the influence of oxygen and ultraviolet light. Light-innduced oxidation of lignin is what turns newspapers yellow after a few days' exposure to sunlight. (Light can also cause some printing inks to fade.)

In acid hydrolysis, the cellulose fibers are cut by a reaction involving heat and acids, resulting in paper that turns brown and brittle. The sources of acidity include lignin itself, air pollution, and reaction by-products from the oxidation of paper. Another major source is alum, which is often used with rosin to prepare the paper surface for accepting printing inks. Alum eventually releases sulfuric acid in paper.

Acidity and alkalinity are measured in units of pH, with 0 the most acidic and 14 the most alkaline. (Neutral pH is 7..00) Because the scale is based on powers of 10, a pH of 4.5 is actually 200 times more acidic than a pH of 6.5. Fresh newsprint typically carries a pH of 4.5 or less, while older more deteriorated paper on the verge of crumbling, may run as low as pH 3.0. Although some modern papers are made acid free, most paper collectibles are acidic and need special treatment to lengthen their lives.

Other factors which contribute to the destruction of paper include extremes of temperature and humidity, insects, rodents, mold and improper handling and storage.

                                                                                         Cont'd Part 2