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Question: How can old postage stamps be protected from the effects of temperature, humidity, and pollutants?

Quick Answer: You cannot eliminate the damage caused by the effects of the environment on your rare stamps of the world, you can only hope to minimize it - the stamp information on this page will help you do so.







Temperature, Humidity and Pollutant and their Harmful Effects on Collections of Old Postage Stamps

For those that wish to skip over the hot, humid, and somwhat dense detail below, the lesson taught below is this: although the effects of temperature and humidity can be difficult to fully understand, and expensive to fully control; you can nevertheless minimize and slow the damage that your old postage stamps are at this very moment experiencing by following some easy to implement steps.

The photos, charts, and discussion below provide examples of the types of environmental damage your collectible stamps, philatelic collections, and art can be subject to on a daily basis.

chart showing tmeperature vs relatie humidityYou can never hope to completely shield your philatelic stamps from pollution temperature, and humidity, however, you can slow their harmful effects. The graph to the left helps to visualize the damage that particular combinations of relative humidity (RH) and temperature can cause to philatelic materials that are exposed to hydrolysis (i.e. repeated water vapor de/absorption by paper, stamps, prints, etc.). As one moves upwards along one of the curves in the graph, every combination of temperature and relative humidity will cause philatelic degradation at the same rate. For example, along the curve marked x4, four times as much damage will be experienced by stamps in stamp album pages as compared to the curve marked x1. The area below the purple overlapping 4C dew point curve is inaccessible to the average climate control mold growth chart system. Only the most expensive of systems can establish climactic conditions below the purple curve. For example, 8C at 75% RH and 18C at 40% RH are achievable by the average air conditioner/dehumidifier, but not 8C at 40% RH. Another point to note is that low temperature and high humidity will cause less damage to your philatelic stamps than high temperature and low humidity. But if my stamp album pages are stored in high humidity conditions won't they be exposed to mold growth? The graph to the right illustrates that mold growth is dependent on temperature, and that high humidity can be tolerated by old postage stamp collections as long as temperature is kept relatively low; in other words, as long as you keep your climactic conditions below that represented by the area below the solid black line in the graph presented to the right.


Protective steps that you can take to protect the philatelic value of stamps and art from the environmental effects of temperature, humidity, and pollutants:

  1. When storing and displaying your stamp collecting albums, if given a choice of low humidity and high temperature, or high humidity and low temperature, generally the latter is preferred (see discussion and graphs above).

  2. Similarly, maintain a stable relative humidity, which will reduce repeated de/absorption of water vapors, which over time can also destroy your collectable stamps.

  3. Do not attempt to maintain a very low, or no, humidity environment. By doing so, hydrolysis susceptible items (eg. your united states postage stamps) can dry to the point of becoming brittle to the touch.

  4. Maintain the stability of the temperature that your philatelic and stamp items are stored and displayed in; by doing so, temperature induced contraction and expansion of your old postage stamps will be reduced, which will in turn reduce the mechanical stresses and strains that will eventually rip your philatelic collection apart.

  5. For paper based philatelic collections many museums try to maintain a stable temperature of about 68 degree F, and depending on the season, a relative humidity between 30-55 RH.

  6. Lastly, the above suggestions have been formulated in the context of collections that are susceptible to hydrolysis (i.e. paper, stamps, art, prints, etc.). The effects of temperature, relative humidity, and pollutants become much more extreme and difficult to predict and, thus, more important to control, particularly when considered in the context of use with other stamp collecting supplies (see Effects of Paper and Effects of Plastic).

So given the information above, what might some of the reasons be that the rightmost Scott #523 stamp below has suffered oxidization damage. Both images of the #523 were posted on a respected philatelic web site during a discussion about the types of plastic materials that are typically sold and used by philatelists for storage and display of their collections. The discussion generated a large amount of information, but no final conclusions. The stamp image of oxidized stampon the left can be seen to retain its original orange red color, while the stamp on the right is seen to have lost this same color via oxidization. If it had been indicated during the discussion that the stamp on the right had been stored in the plastic holder shown on the page dealing with Effects of Plastic, the oxidized condition of the stamp might possibly be explained by chemical decomposition of the supposedly "inert" plastic the holder used to store this stamp was made from. For example, if sulfurous compounds were used in the manufacture of the plastic holder, the oxidized appearance of the stamp on the right above could be explained by interactions that might have occurred between the compounds and the stamp's ink (a known process by which certain fugitive orange and red inks are susceptible to). On the other hand, archive grade PET "Mylar®" polyester plastic holders (to the extent tested and standardized by the Library of Congress) are considered to be "inert." Because it was indicated by the auction house that the stamp on the right was stored in an "inert" plastic holder, presumably the oxidization damage could not have been caused by degradation of the plastic holder itself. Unfortunately, only conjecture is possible, as all the added information that would be needed to make a final conclusion is not available. Nevertheless, some hypotheses are formulated for your consideration below. However, before proceeding to the hypotheses, consider, if you will, some more information about effects the environment can have on your postage stamp values:

Certain lead components in particular ink colors tend to react with sulphur hydrogen, which comes to the air when organic material is decomposing. This sulfer may originate from paper products (including the paper stamps are made from), forms of rubber or plastic, adhesives, and pollutants in the atmosphere;

Plastic, whether "inert" or not, is permeable. Reactive gases and pollutants will over time, diffuse from outside to within a plastic holder or mount (PSE slabs included); take this into consideration when storing or displaying philatelic and stamp collections in a smoke filled or polluted atmosphere (Los Angeles ... ). Also, take into consideration that because these processes occur over time, "im/permeable" should be considered a relative term;

To satisfy the requirements of the Library of Congress, archive grade PET "Mylar®" plastics cannot contain any UV inhibitors, which can decompose and cause damage over time. Thus, if intended to be placed in physical contact or to be used in close proximity to your stamp collection, your archival PET 'Mylar®" polyester plastic products should not be expected to provide any protection against UV light (see Effects of UV light);

When a semi/sealed plastic mount or holder is used for storage or display of collections, any by-products of the decompostion the collections may expereince may become trapped within the interior space of the plastic holder or mount. Unless the plastic mount or holder is allowed to breathe, a "micro-climate" can become formed within the holder. The formation of such a microclimate can act to amplify the decomposition of the philatelic stamps and/or that of the plastic compounds the mounts or holder are made of. The implications of sealing paper within a micro-climate has only recently been studied and has been identified as also being capable of being formed between the semi/sealed paper pages of stamp albums and in philatelic storage containers;

Even 100 years ago it was noted that many classic stamps changed colors and oxidized when subject to humidity. Because water vapor can enter or diffuse and become trapped within the "micro-climate" of a semi/sealed plastic holder (as well as within the semi/sealed paper pages of stamp albums, philatelic storage containers, etc), philatelic and stamp items may inexplicably and seemingly overnight be oxidized or damaged;

Every time a stamp is dipped in watermarking fluid, every time it is "brightened" with peroxide, every time it is "cleaned," every time it is touched, every time it is rinsed in tap water ... is one more accelerative step toward its destruction. The residues from each of these events are cumulative, and in combination with environmental factors discussed above and below, WILL accelerate your philatelic collection's eventual demise.

There are many ways that environmental factors can damage your philatelic collection. In combination with use of paper and plastic products that are not alkaline buffered or archive grade PET polyester plastic (Mylar®) based, the damage will be accelerated. By failing to consider and act on this information, the time that you have left to enjoy your items of philately may be shorter than you realize.

Some hypotheses and explanations that may help explain the damage suffered by the stamps above and below:

Hypothesis: to the extent archive grade PET "Mylar® polyester plastic holders are permeable, the oxidized stamp on the right above was exposed to a sulphur hydrogen rich atmosphere, which evenly diffused through the plastic holder to cause its oxidization. Explanation: a low probability event - presumably the professional office environment that the stamp was stored in precluded its exposure to atmospheric pollutants of this variety. Note: the conclusion should not be construed to imply that "your" philatelic collection will not be subject to damaging atmospheric pollutants - for example, from use of cigarettes in the vicinity of your stamp collection, or a city environment where smog is common, or even from sources of ozone.

Hypothesis: to the extent that archive grade PET "Mylar®" polyester plastic is permeable, the stamp on the right above was stored on, or in the vicinity of acidic, acid free, or pH neutral paper, which decomposed due to environmental factors to a point that it produced harmful by-products that diffused through the plastic holder to cause the oxidization damage that is shown. Explanation: in view of all the many supposedly "safe" philatelic paper products that are currently being sold and used, this last hypothesis is within the realm of possibility, however, presumably the party that stored this stamp in the plastic "inert" holder knew not to do so in the vicinity of acidic paper. Note: the lesson taught by this hypothesis can be avoided if, from the start, the use of all but archive grade alkaline buffered philatelic paper products is eliminated. This warning applies as well to those clear "inert" plastic products that are sold with paper backing, in which case both paper and plastic should be verified to be archive grade alkaline buffered and PET "Mylar®" polyester plastic.

Hypothesis: the stamp above on the right was exposed to ultra violet (UV) light, which caused its inks and/or paper to decompose. Explanation 1: because PET "Mylar®" does not contain any ultraviolet UV inhibitors, and if the stamp above was over exposed to ultra violet (UV) light, the stamp would probably first evidence direct damage via fading, not oxidization, but fading is not evidenced by the stamp. Explanation 2: if the plastic holder used to store the stamp was not "inert," the holder itself could decompose from reactions caused by the UV light, the by-products of which could then oxidize the stamp. However, there was no discussion by the stamp auction firm as to the actual type of plastic holder used and, therefore, no conclusion is made in this regard. Note: although ultraviolet (UV) light is commonly mentioned as being a cause of damage, it MUST be remembered that both UV light and VISIBLE light cause damage, and in most cases exposure to VISIBLE light will be the primary cause of stamp damage (see Effects of VISIBLE light and Effects of UV light).

Hypothesis: the stamp to the right above was stored in a temperature and/or humidity that was not properly controlled, with either or both factors being the cause of decomposition of the acidic paper of the stamp, which in turn caused accelerated oxidization of the stamp. Explanation: the fact that the stamp is evenly oxidized across its surface is some evidence that the oxidization may have been caused by an evenly applied outside factor, such as from improper temperature, humidity, or pollution. Because the stamp could have been stored in an environment that had the wide changes in temperature over night and day, and week to week, as typically occurs in commercial office buildings, it is within the realm of possibility that the damage could have been caused by storage in, and exposure to, uncontrolled environmental conditions. Note 1: the conclusion reached above would be strengthened if the stamp was stored in a sealed holder. Note 2: if the stamp in question had been dipped in stamp fluid, cleaned with peroxide, washed in tap water, or exposed to any number of other countless tortures, the residues from all these factors could have built up to the point that the above damage to the stamp was further accelerated. Before repeating these sins, consider how many times did each previous owner of the stamp conduct such chemistry experiments, such as you might now be tempted to perform, in which case, is it any wonder why the stamp shown above (or the one that may presently be before you) might have, or be ready to, give(n) up its orange red color?

Hypothesis: to the extent an archival PET "Mylar®" polyester plastic holder is impermeable, such a holder containing the stamp could not "breathe," and harmful by-products (from decomposition of the acidic stamp paper or polluted air within the micro-climate of the holder) caused or accelerated damage of the stamp. Explanation: the fact that the stamp is evenly oxidized over its entire surface may be evidence that it was stored within a completely sealed plastic holder, which could cause the evenly distributed damage that is evidenced over the entire surface of the stamp. However, there is no confirmation of this fact, and a just as possible scenario could be that the plastic holder was only of the semi-sealed variety, where at least one edge of the plastic holder was unsealed, in which case the damage evidenced would be more difficult to explain.

Hypothesis: in semi-sealed plastic holders, chemistry related damage typically begins to first appear (and is more pronounced) around the unsealed edges of the holder. Explanation: This type of damage can appear when stamps are stored in plastic holders of the semi/sealed variety (for example as seen on the Effects of Plastic page). With semi/sealed holders, air from outside first enters the holder along its unsealed edges; if sulphur compounds (that can be released by the holder, be present in the air, or in the stamp) are present, chemical reactions can occur and can be evidenced as oxidization that first appears along the corresponding edges of the stamp.

Your philatelic items and stamps can be damaged by the effects of temperature, humidity, and pollutants. Whether they be stored or displayed using paper, plastic, or some other means, these effects can only be exacerbated by exposures to VISIBLE and UV light, which are discussed on the pages that follow.


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