The Arthur Salm Foundation

Report No. 3

Plastics, Paper Permanence, and Hinges

Plastics

The Arthur Salm Foundation conducted a 2½ year preliminary study of the plastics used in philately, but have not been able to arrive at definitive conclusion. There are many variables involved in the manufacture of the plastics used for philatelic purposes. The task of defining more precisely which materials are better suited for philatelic archival purposes to be beyond the relatively limited resources of the Foundation at this time appears.

‘Archival’ is a non-technical term remaining without a consistent definition. The term implies some form of preservation, with ‘preservation’ being defined as an extension of an object’s life beyond its normal lifetime by using enhancing materials and techniques in addition to the object’s normal environmental conditions. Such materials are expected to be durable and chemically stable under the anticipated conditions. There are no universal standards defining the time period an archival material should last, and under what conditions or how it will assist to preserve materials that were not originally intended to last.

To the philatelist, the term ‘archival’ implies an environment that will permit most stamps and covers to remain in their original state for several generations, or even for several hundred years. Unless they are professionally treated, stamps printed on highly acidic paper, or those with self-sticking adhesives, most likely will decay even if using the finest archival mounting and atmospheric conditions. Even in this case, they probably will not last as long as similar material manufactured from acid-free components. A preservation technique that is deemed reasonable to enhance a stamp’s preservation possibilities by one individual may not be deemed to be reasonable by another. For example, most stamps would exhibit a better survival rate without their gum, but few collectors wish to remove a stamp’s gum.

The long term preservation of papers involves contact with neutral materials that are free of acid and alkaline salts, and do not change when exposed to environmental conditions such as storage temperature, relative humidity and air quality, as well as with time. Light, especially sunlight, is particularly detrimental, as it can be a catalyst to further promote chemical reactions. Handling of the stamps should be kept at a minimum, since simple flexing enables the weakening of the paper’s fibers and, in extreme cases, can cause the printing ink to flake.

Most philatelic protective materials are manufactured using plastic films, particularly when transparency is of value. The molecular structure of these plastic polymers can be directed to create a wide variety of properties in the finished products. Additives also are added to manufacture a commercial composition having specific finalized properties. There are numerous plasticizers, slip agents, stabilizers and inhibitors that can be added to most plastics before they are added into the films destined to be used as hobby materials. Beyond that, there are wide variations in stamp inks, paper gum, overprint and taggants (a chemical or physical marker added to materials to allow various forms of testing), each of which can affect a stamp’s interaction with the plastic.

Collectors Club of Chicago’s members have studied numerous worldwide publications issued during past years evaluating ‘protective films’ as they are used in philately. The reports were both in the English and in foreign languages. The foreign language references were professionally translated, and all of the reports were examined and discussed. An extensive laboratory evaluation of various plastic materials was commissioned, and a 30-page report was submitted to the Board of Directors of the Collectors Club of Chicago’s Salm Foundation. After a comprehensive study by the Foundation’s board of polymer experts, the laboratory report was found lacking in several important areas, and unscientific in its experimental conclusions. That study will not be published.

At this time, the only specification by a recognized scientific body that can be recommended to the hobby of philately is that of The United States Library of Congress Preservation Office, which has strict requirements for ‘protective films’ used for their archival storage purposes: “The composition must be clear, colorless, biaxially oriented / stressed / drawn polyethylene-terephthalate film, such as DuPont Mylar© D, Melinex© 516 or equivalent. The clear and colorless polyester film must not contain any plasticizer, surface coatings, UV inhibitors, or adsorbents, and be guaranteed to be non-yellowing with natural aging. As received, the film must not contain any coloring agents. A certification of compliance with the above requirements must accompany the shipment” (United States Library of Congress Specification No. 400-005-1/93).

Testing for Paper Permanence

Prior to the testing procedures, the samples were conditioned at a standard Technical Association of the Pulp and Paper Industry (TAPPI) temperature of 73ºF and 50% relative humidity; all of the requested qualitative and quantitative test procedures were performed in accordance with standard TAPPI testing methods. The test results applicable to the submitted samples are given in the following data tables.

Permanence of paper refers to the chemical stability of paper, and its ability to maintain its initial properties over a long period of time; it can be measured by an accelerated aging test in the laboratory. In a typical test, the paper is heated in a circulating forced air oven at 105ºC for seventy-two (72) hours. Under these storage conditions, the time and temperature is equivalent to twenty-five (25) years of normal paper aging. During this project, the material was aged eighteen (18) days, which would be equivalent to 150 years of normal aging. It was observed that alkaline-grade papers had a better permanence / longevity / shelf life than did the ordinary acid papers.

There are two manufacturing methods of producing alkaline grade paper. In the first method, alkaline-filled paper containing calcium carbonate is used. This paper has a pH value in the range 7.5 to 9.5, and contains a reserve amount of buffering capacity. The buffer acts to neutralize the acidic chemicals that come in contact with the paper, or are produced in the paper during the aging process.

In the second method, an alkaline-sized paper has been sized (chemically treated) in an alkaline paper machine system. This paper has a pH of 7.0 or higher, and can be marketed as-is, or further coated with calcium carbonate to impart an alkaline reserve.

In the laboratory, a paper sample is tested for pH (the acidity-alkalinity reading) by the cold extraction method. If the pH is found to be in excess of 7.0, the paper sample is considered to be an alkaline grade paper stock. This type of paper is subjected to an additional analytical procedure named the ‘Alkaline Reserve Test’, in which the amount of calcium carbonate present in the sample is determined.

Alkaline grade papers are of interest to the philatelist. They should be used to mount major philatelic items. If these stamps and covers are mounted on an acidic paper, the acidity will transfer by osmosis to the mounted items over a prolonged time of storage, and will cause physical degradation of the philatelic items ranging from minor to major.

Hinge Testing Procedures

Stamp hinges were manually affixed to an alkaline-grade paper. After six days of aging at room temperature, the hinges were removed, and were evaluated for peelability and tear tendencies. The sampled hinges were rated for taste during the mounting procedures.

~ 100% peelable is defined that the stamp hinge was readily and entirely removed from the stamp alkaline-grade paper.

~ 100% tear is defined that the stamp hinge tore, leaving a small portion of the hinge on the stamp alkaline-grade paper. The tear pattern was observed on all the stamp hinges tested during this particular sampling.

~ 100% peelable and 100% tear is defined as the extremes in which the stamp hinge is completely removed in one case, and remains adhered in the second case.

1st Edition, April 1995; 1st Revised Edition, June 2015.