HOW TO PRESERVE AND STORE YOUR MOVIE POSTERS
By William M. Cole, P.E.
Movie Poster collecting today is for both fun and profit. Yet, the poster you thought was going to increase in value year after year could suddenly turn yellow after only a few months, rendering it 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 has plant fibers that have been reduced to a pulp, suspended in water and then matted into sheets. The fibers 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 papermaking over the years, most paper products today are made from wood pulp.
Wood pulp comes in two basic varieties: groundwood 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 groundwood is the cheaper of the two, it is the primary component in such inexpensive papers as newsprint, which is used in many newspapers, magazines, and yes, movie posters. Chemically purified pulps are used in more expensive applications, such as stationery and some magazines and hardcover books.
Since groundwood 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-cellulosic 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 causes 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 groundwood paper breaks down quickly under the influence of oxygen and ultraviolet light. Light-induced oxidation of lignin is what turns newspapers yellow after a few days of 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 posters and other items in an air conditioned room, if possible, and regularly monitor the humidity. Excess humidity should be controlled with a dehumidifier. Storage materials such as envelopes, sleeves and boxes, should be of archival quality to prevent contamination of their contents.
Polyethylene and Polypropylene
For years collectors have stored their posters, lobby cards, and other material 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. Both polyethylene and polypropylene contain solvents and additives in their manufacture to assure clarity and increase the flexibility of the plastic. Polyethylene, when uncoated without any solvents, is 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 as "archival quality". This, unfortunately, is untrue. 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, long-term 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 aging. Many advertisers claim that their boards are "acid-free at time of manufacture." In reality, these products are spray coated with an alkaline substance making them acid free for only a short time. Boards termed "acid-free at time of manufacture" do not offer sufficient protection or storage for anything other than short term (3 - 5 years). 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 decidify them before storage. Decidifying sprays and sollutions are now available for home use. By impregnating the paper with an alkaline reserve, you can neutralize existing acids and inhibit oxidation, future acidity and staining due to certain fungi. However, it is best left to the professionals to decidify your paper collectibles. Decidification with proper storage conditions will add centuries to the lifetime of paper.
In summary, we recommend the following guidelines for the maximum protection of your collectibles: