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.

Guidelines for Preservation

First and foremost, keep your paper collectibles cool, dark and dry. Store books and other items in an unheated room, if possible, and regularly monitor the humidity. Excess heat and humidity should be controlled with an air conditioner and a dehumidifier. Storage materials such as envelopes, sleeves and boxes, should be of archival quality only to prevent contamination of their contents.

Polyethylene and Polypropylene

For years, collectors have stored their comic books, postcards and other collectibles in polyethylene bags, PVC sheets and plastic wraps. Although such products may be useful in keeping away dirt, grease and vermin, many plastic sleeves contain plasticizers and other additives which can migrate into paper and cause premature aging. Booth polyethylene and polypropylene contain solvents and additives in their manufacture to assure clarity and increase the flexibility in the plastic. Polyethylene when uncoated without any solvents s a good moisture barrier but has a high gas transmission rate, and eventually shrinks and loses its shape under warmer conditions.

In recent years polypropylene bags have been sold under the guise of being archival sound. This is far from the truth. Only uncoated and untreated material is suitable for archival protection. Currently, the only way to seal polypropylene is to add a substance called PVDC (Polyvinyl Dichloride which is a relative of PVC) to allow the material to be heat sealed. Therefore, once you add the harmful additive, the sleeve now becomes non-archival and should not be used for long term storage.

Mylar

According to the US Library of Congress, the preferred material for preserving valuable documents is uncoated archival quality polyester film, such as Mylar type D by DuPont Co. or equivalent material Melinex 516 by ICI Corp. Mylar is an exceptionally strong transparent film that resists moisture, pollutants, oils and acids. With a life expectancy of hundreds of years, Mylar will outlast most other plastics. In addition, the brilliance and clarity of Mylar enhances the appearance of any paper collectible.

Acid Free Boards and Boxes

Because ordinary cardboard is itself acidic, storage in cardboard boxes may be hazardous to your collection, and is a leading cause of premature deterioration of paper collectibles. For proper storage, only acid free boards that meet the US Government's MINIMUM requirements are acceptable. These requirements have been defined as boards having a 3% calcium carbonate buffer throughout and a minimum pH of 8.5. Anything less will hasten your collection's destruction. While many advertisers claim that their boards are "acid-free at time of manufacture," they are in reality only spray coated with an alkaline substance making them acid free for only a very short time. Boards termed "acid-free at time of manufacture" do not offer sufficient protection or storage for anything other than short term. True acid-free boards have been impregnated with a calcium buffer resulting in an acid-free, alkaline pH content of 8.5 throughout.

Another way to extend the longevity of your collectibles is to de-acidify them before storage. De-acidifying sprays and solutions are now available for home use. By impregnating the paper with an alkaline reserve, you can neutralize existing acids and inhibit oxidation, acidity and staining due to certain fungi. However, it is best left to the professionals to de-acidify your paper collectibles. De-acidification with proper storage conditions will add centuries to the lifetime of paper.