The following article presents a fascinating scientific study of the various methods of stamp soaking for classic stamps and their archival benefits by co-authors Stanley Brown (@stainlessb) and Christopher Dorn (@berylliumguy). The article was submitted by APS Chapter The Stamp Forum as an Article of Distinction for 2024 and originally appeared in volume 8, no. 1 (October-December 2023) of The Stamp Forum Newsletter.
To learn more about The Stamp Forum, click here.
To read other Articles of Distinction, click here.
Introduction
Members of The Stamp Forum (TSF) already familiar with Stan and Chris know that they both collect stamps from the Classic era. Chris recently began a serious study of the Cape of Good Hope Triangles, while he continues to maintain his longtime collections of Hong Kong, Germany, German States and much more. Stan focuses principally on France, Belgium, and Victorian era Great Britain.
While pursuing their individual collecting interests, like many of us, both have encountered stamps in less- than-pristine condition, perhaps stuck to an old album page or envelope, heavily hinged or just plain dirty, thus requiring some method of removal and/or cleaning. Soaking would be the obvious method of choice, but the authors’ concern for proper archival treatment of these stamps, as the historical artifacts which they are, has played an important role in their pursuit to find soaking methods that would result in the best outcome with the least amount of damage.
The Authors’ Perspectives on Soaking: Chris
I originally started soaking stamps in tap water to remove them from their envelopes when I first started collecting back in the 1960s-1970s. I didn’t take any particular care with the process back then, and I made my share of beginner’s mistakes, such as ruining stamps by leaving them in water for too long or failing to separate out stamps that were affixed to non-colorfast envelopes, and thus staining all the stamps in the batch as a result.

Figure 1: Examples of album pages from old, mounted collections, sometimes with stamps almost all completely stuck down. On some occasions, the only way to remove these stamps safely from the page without risking (more) damage is to immerse and soak the entire sheet at one time.
Once I started buying stamps from dealers, as an adult collector, I thought that my soaking days were pretty much over, but I was wrong about that. In the early 2000s, I was buying old mounted collections and in order to clean up my new acquisitions, I was back to soaking stamps on a regular basis again, but now it’s mainly to remove hinges or separate stamps that are stuck down to old album pages (see Figure 1 above). I am pleased to report that I have improved my technique since then and now I get good results the vast majority of the time.
Now, with more than 50 years of experience in collecting stamps, I see soaking stamps as a very valuable tool in conserving them properly by cleaning them and revealing their condition and other qualities. While all of this seems perfectly logical and reasonable to me, I note that soaking, even just in water, can be a controversial subject among philatelists. There is at least one well-known US dealer who has mentioned more than once in his monthly emails that he believes that every time a stamp is soaked in water, its color is diminished and that repeated soaking will permanently ruin stamps.
In addition, there are also well-known specialist collectors of Cape of Good Hope Triangles who have stated publicly that they do not recommend soaking these stamps in either water or dilute hydrogen peroxide, due to fears of diminishing the color and possibly the bluing of the paper, if it is present. With these claims of potential downsides to soaking in mind, I looked for references of any studies or controlled experiments that supported those opinions, but I didn’t really find much.
That said, there is good, basic advice available, which warns about the beginner’s mistakes mentioned earlier and which raises awareness of the existence of fugitive inks (i.e., inks that are soluble in water or other chemicals). Fugitive inks were used primarily on stamps of Great Britain and the British Commonwealth in the 19th and early 20th Centuries to prevent fraudulent re-use of stamps by removing the cancellations using chemicals. Fugitive inks are an important consideration when soaking stamps, but an in-depth discussion about them lies outside the scope of this study.

Figure 2: When soaked, the printed design of stamps with fugitive inks may completely dissolve and disappear, but it can also just fade depending how long the stamp is in contact with the solvent. This image shows a progression on Great Britain Sc117: Left: An unused copy with full gum that has never been in contact with water, showing original colors. Middle & Right: Used copies of GB Sc117 that have been in contact with water, showing a faded green central vignette compared to the pristine example.
The Authors’ Perspectives on Soaking: Stan
Like Chris, I originally soaked stamps in tap water long enough for the stamp to loosen and “slide” off the paper. There was no rinsing or blotting, the stamps being placed most often on a magazine cover which had the glossy/coated paper and then another on top with a book and left for a day. It wasn’t unusual to have to cut the magazine cover apart and re-soak some of the stamps. I learned early on that red paper envelopes (common around Christmas) could turn everything somewhat pink, so for the most part, I learned to avoid those.
As I started getting approvals and dealers books, soaking was seldom necessary. Thanks to my aunt’s, uncle’s, and grandmother’s generosity, most “new” US issues were given to me as gifts that they would buy from the post office.
Fast forward to my most recent return to stamps, which has come as a result of inheriting material from those relatives who had encouraged me in the beginning. I found myself with a great many stamps on paper, or worse yet, blocks of formerly mint stamps all stuck together from dampness. So back to soaking stamps, initially just with tepid water, blot with a cloth towel and then place between paper towels. This worked, but often aside from now being unstuck, the stamps still looked “dirty.” In addition, I noticed that press-flattening the stamps between paper towels with embossed patterns in them didn’t give an especially attractive result. Reading threads on TSF, I discovered that many other practitioners were using hot water and a drop of clear detergent, and some were even using hydrogen peroxide.
My familiarity with hydrogen peroxide was limited to watching it foam up on a cut or scrape in its use as a medical treatment, as well as its industrial use as a disinfectant in high-purity process systems. Based on what I read on TSF, many were diluting it, and most were leaving the stamps in the diluted solution for a minute or less. Was there a hard-and-fast rule for using peroxide on stamps?
Chris and I had a side discussion and one thing led to another with a decision to work together to determine if there was a “best practice” (more my interest) and whether blued paper, specifically COGH (Cape of Good Hope) issues printed by Perkins Bacon (more Chris’ interest), would actually be negatively affected if exposed to hydrogen peroxide.
The Framework
Several back-and-forth discussions followed: which stamps to try this on? What protocols to follow? Both of us were interested in something that others could also try for themselves and basically be able to reproduce the experiments at home and confirm the same results as we got.
We felt a “control” condition of water only was essential, just in case there really wasn’t that much of an advantage to using hydrogen peroxide. It was suggested that faulty material and space-fillers be used so that if the stamps were damaged due to the soaking process, we would not be destroying sound philatelic material.
So, we both set out to find two examples each from a variety of classic stamp issues to be used as test specimens. One specimen of each pair would see only water, and the other would see full-strength 3% hydrogen peroxide. Each specimen would be scanned before and after each exposure condition at as close to the same field size as possible. To show as much detail as possible, all stamps were scanned front and back at 3600dpi (dots per inch). See Figure 3 for images of the stamps in the two main groups.
With paired groups of early stamps from various countries, the next decision was to determine the soaking parameters. For the Control Group, we decided to use carbon-filtered tap water, with the idea in mind that filtration might eliminate, or at least reduce, any chlorination found in untreated tap water and the potential impact that it might have on the results. Some TSF members had commented about concerns of using chlorinated water when soaking.
The hydrogen peroxide used was rated 3% USP. (USP stands for United States Pharmacopeia; it is a designation found on many products intended for medical use to show that it was made to reliable quality standards [1].) Each new soaking period started with fresh solution. The study was also begun with brand- new/factory-sealed bottles of hydrogen peroxide. The decay rate of a sealed/closed bottle is low (0.5%/year) [2], meaning that it can have a reasonable shelf life, but in the interest of repeatability of the experiment and consistency of the results, it made sense to begin with a fresh bottle rather than one previously opened and whose composition might have changed.
Identical silicone rubber dishes and two Desert Magic II drying books were used. One for the Control Group stamps (soaked only in water) and the other for the “treated” stamps, i.e., those soaked in 3% hydrogen peroxide.

Figure 3: The test specimens, prior to any soaking in this study. Left: This is the Control Group, which would only be exposed to filtered water. These test specimens are numbered W-1 through W-17. Right: This is the Peroxide Group, which would only be exposed to full-strength 3% hydrogen peroxide solution. These test specimens are numbered P- 1 through P-18.
Readers please note: The reason there is one additional Cape Triangle in the Peroxide Group is because Chris only had one damaged stamp with evident bluing on the reverse. As peroxide soaking was particularly suspected to diminish the degree of bluing on these issues, it was decided that this one available test specimen would be included in the Peroxide Group rather than the Control Group. A Great Britain Penny Black was also added to the Peroxide Group near the end of the study. Because it was added later in the study, it does not appear in the scans above. Please see Table 1 below for the complete list of the test specimens.
Table 1: Soaking Study test specimen identification table.

Notes:
- Cape of Good Hope Sc4-4a are equivalent to SG6-6a
- Cape of Good Hope Sc2a is equivalent to SG2 (Deeply Blued Paper)
- Great Britain Sc1 (P-19) was added later in the study

Figure 4: As previously described by Stan, silicone rubber dishes of identical design were used for the study, the one on the left (yellow) for soaking the test specimen in filtered water, and the one on the right (green) for soaking its specimen in full-strength 3% hydrogen peroxide.
Setting Up the Study
After the test-specimen stamps were contributed by both authors, it was Stan who offered to set up the experiments and run them. Please see Figure 4 above for a photo of the experimental test set-up prior to the start of the trials.
Every effort was made to avoid introducing any external contamination into either the water or hydrogen peroxide used for the soaking process. Both liquids were used at room temperature. The dishes were cleaned in between uses, and they were also kept in a clean environment while in use. Stan kept everything used during the study separate from his “normal” stamp collecting materials and accessories, even so far as using dedicated tongs/tweezers for each Group, i.e., water and peroxide.
The Design of Experiment (DOE)
Initially, we had thought of various time periods for the soaking, starting with as little as 1 minute, and eventually progressing up to as long as 10,000 minutes (just under a week). One minute at the low end seemed logical, particularly for the 3% hydrogen peroxide, as this was a duration reported to have been used by TSF members for reversing discoloration due to sulfurization (aka sulfuretting) on affected stamps. Chris used 1-minute soaks for Cape Triangles (see Figure 5 below) based on the method used successfully by Jim Jackson (@jkjblue), on which Jim reported results in the relevant TSF thread [3].

Figure 5: Left: COGH Sc2 (SG4), 4-pence deep blue on paper more-or-less blued. The discoloration is quite uniform in appearance, which made it more difficult for Chris to identify it. Right: The same stamp with discoloration removed thanks to a 1-minute soak with 3% hydrogen peroxide. The bluing on the back did not show any adverse effects as a result of the process [4].
After further consideration, we decided that 10,000 minutes seemed well beyond the length of time anyone would be soaking stamps. As some members on TSF had mentioned soaking for an hour “or so” as a routine practice (for them), we decided that the 100-minute mark seemed a more logical upper time limit. Eventually, we streamlined the cumulative soak-time increments (in minutes) down to 1, 10, 50, and 100 minutes. A digital timer was used to determine the end of each period. Please see the breakdown on soak times in Table 2 below.
Table 2: Final soaking study experimental plan

The Control and Peroxide Groups were broken down into four smaller batches to simplify handling. Doing that limited the time needed to remove a stamp from its soaking solution and give it a quick rinse (a one- second dip). After rinsing, blotting was done using a thin cotton towel to remove any excess liquid, and then the stamps were placed into the drying books. Using smaller batches also made scanning the fronts and backs after each time increment a bit faster (3600dpi).
The scanner used was an Epson Perfection V600 with VueScan software. The color setting (brightness) was adjusted slightly so that what each of us saw on our own monitors seemed representative. The VueScan setting was then saved and used each time. Stan discovered that placement on the scanner did make a slight difference, so a mask/template was created, so that all scans were done at the same location on the flatbed glass. Image areas were noted for each stamp and maintained through each group. Every effort was made to keep skewing to a minimum, as it slightly changes image size.
Experimental Results & Discussion
Stan: I must admit, based on what I had read and heard from others and despite trying to remain unbiased, I expected lengthy peroxide soaking to damage the stamps. This did not turn out to be the case. There was some observed breakdown of the paper itself, especially at the locations of tears, holes, and severe thins, which started to become noticeable at the 50-minute mark.

Figure 6: From left to right, progressive scanned images of fronts and backs, showing the same stamp, Test Specimen P-7 (Batch 1), and how it looked after each soak in 3% hydrogen peroxide. The “0000” designation indicates that this is prior to any soaking in this study, followed by the cumulative soak times of 1 minute (0001), 10 minutes (0010), and so on. This stamp shows some brightening of its color after 10 minutes, but the paper appears thinner and to be breaking down after 100 minutes.
On several of the damaged stamps, these effects became rather pronounced at 100 minutes. As a result, there was some hesitation after reaching 50 minutes on whether to continue to subject the Penny Black to more peroxide soaking. Although it was a damaged space-filler, it was still a Penny Black. After crossing my fingers (a time-tested technique for avoiding serious problems!), I was relieved to see that the paper of the Penny Black did not degrade any further after the full 100 minutes.
Chris: Like Stan, based on what I had read in Stevenson regarding treatment of Cape Triangles with hydrogen peroxide (he strongly advised against it [5]), I also expected lengthy peroxide soaking, i.e., more than a minute or two, to damage the stamps by degrading the ink on the printed surface. This did not seem to happen. I had also read in another source that prolonged exposure to hydrogen peroxide could dissolve a stamp’s ink and destroy the printing, but this also did not happen when using a 3% solution.

Figure 7: From left to right, progressive scanned images of fronts and backs, showing the same stamp, Test Specimen P-18 (Batch 1), and how it looked after each soak in 3% peroxide. The scans show little change, but it was observed that the printed design and watermark became more visible on the back.
My theory, which I mentioned in a previous article [6], is that in those older publications, the authors were considering what I would call “industrial strength” peroxide, which meant a formulation much stronger than 3%. I deduced that because Stevenson explicitly mentioned that peroxide was also used to remove cancellations from stamps. It is clear from my experience and again from this study that 3% peroxide is not capable of doing that.
Soaking in water after the initial removal of any hinge remnants or adherent paper had no further effects on the stamp. Most hinges released by the 1-minute mark; paper sometimes took longer, with the early Austrian stamps (Specimens W-1, W-5, and W-13) taking the longest to release their adherent bits. With the exception of a few “difficult” stamps, there seems little advantage to long water-only soaks. Whether this will hold true with the addition of a detergent still needs to be tested.
In Stan’s professional experience with hydrogen peroxide (he worked with it during his career in the metals industry), he found that it is known that the solution can start to decay in the presence of other organic compounds, thus reducing its effectiveness. Therefore, soaking in water, either with or without using a drop of mild detergent, to clean the stamps’ surface, is recommended prior to soaking in hydrogen peroxide.
Such a practice should maintain the 3% peroxide solution as close to its full strength as possible. Please note: it is possible to find hydrogen peroxide in solution strengths greater than 3%, but we would generally advise against using any of those for cleaning stamps. We also recommend testing the peroxide solution on damaged or low-value, expendable stamps first, before committing one’s collection keepers to the soaking/cleaning process.
Visually, results after soaking in 3% hydrogen peroxide seemed the best after 10 minutes. Any improvement with a longer soaking time seemed insignificant, with the exception of some types of stains on the backs of some of the stamps. The concern that exposure to peroxide would diminish the color intensity of the blued paper on early Perkins Bacon issues seems totally unfounded when using a 3% solution.

Figure 8: From left to right, progressive scanned images of fronts and backs, showing the same stamp, Test Specimen P-16 (Batch 2), and how it looked after each soak in 3% peroxide. Prior to soaking in this study (0000), the scan shows some pinkish bleeding of the red ink in the margins and on the head, which was reduced after 10 minutes and gone by 50 minutes cumulative soak time. In addition, as with some of the other specimens, the paper started to break down, in this case after just the first one-minute soak in 3% peroxide, and it became much worse where it was already thinned.
Conclusions
Stan: The study clearly demonstrates that soaking in fresh, full-strength 3% hydrogen peroxide for up to 10 minutes did not degrade the tested stamps, as previously suggested by others. For soaking periods longer than 10 minutes, the noted effect was a breakdown of some of the paper, as it generally seemed to become thinner, and any previously damaged areas were made worse. We wonder if that could be due to a reaction with the sizing agents used in some of those early stamp papers (1840-1900?). But the bottom line is that the printed design itself did not become progressively diminished or faded as we had been led to believe.

Figure 9: From left to right, progressive scanned images of fronts and backs, showing the same stamp, Test Specimen P-12 (Batch 4), and how it looked after each soak in 3% peroxide. Stan observed that this stamp showed best improvement to its color by the 10-minute mark, little change at 50 minutes, and some fading by 100 minutes of cumulative soak time. On the other hand, Chris has arrived at the conclusion that when it comes to discerning subtle color differences in these scanned images, Stan’s powers of perception far exceed his own!
All Peroxide Group test specimens were given a quick rinse in fresh (filtered) water, but in fact, this was not necessary, as hydrogen peroxide decomposes relatively quickly in the presence of air. Written chemically, this is expressed as 2H2O2 --> 2H2 + 2O2↑. As previously stated, the study seems to show that 10 minutes is a safe length of time for cleaning with 3% peroxide, but this is not a hard-and-fast rule, as it is not clear at what point between 10 and 50 minutes (cumulative) that apparent thinning of some of the paper occurred. We also did not check paper thickness prior to the study, as we had not expected that changes in paper thickness might occur. On top of that, we did not have any devices for checking paper thickness available to us for the same reason.
Chris: It is clear that I still have more to learn about soaking in general and use of 3% peroxide in particular. On the soaking side of things, I have only ever added liquid detergent to the water on one or two occasions, but I have been impressed with the results I have seen from other TSF members, especially Stan and Torbjørn (@tobben63) [7][8]. As I am now frequently working with classic stamps culled from old mounted collections, they often look dull and/or dirty to me, so a better cleaning process definitely seems in order.
As for 3% peroxide use, prior to this study, I had only ever considered it for reversing the effects of sulfurization and not for any other purpose. Stan had once recommended it to Jean (@polarbear) on TSF for removing mildew from stamps, but it was not tried, at least on that occasion [9]. These days, Stan uses 3% peroxide as part of his routine process for cleaning stamps, which had never occurred to me. I will now be reconsidering my own soaking/cleaning process to decide whether I want to include 3% peroxide use or not, but at least now I have a sound basis for believing that it is safe to do it, should I decide to go in that direction.
Future Work
With all of that said, where do we go from here? For starters, if we want to determine if the apparent visible thinning of some of the papers is real, we need to repeat the peroxide soaking sequence but take measurements of the paper thicknesses, which could probably be accomplished by using calipers of some sort or even by weighing each stamp on a very sensitive scale (balance). The cost of the tools or equipment to do that might make it unattractive, however.
Concerns regarding chlorination in tap water used for soaking were also not tested in this study, as we used a filter to eliminate chlorination as a variable. Like hydrogen peroxide, chlorine is a bleaching agent, but concentrations found in tap water are several orders of magnitude lower than the 30,000ppm of hydrogen peroxide found in the 3% solution (typically 4ppm maximum [10]). We speculate that the
<4ppm of chlorine found in most tap water would not adversely affect stamps during soaking, using an extrapolation based on the 3% peroxide results, but that would not seem to be a scientifically valid proof, so we acknowledge that the specific case for chlorine would need to be demonstrated in order to justify that conclusion.
Another area of interest to both co-authors is that of stamps printed with fugitive inks, which could be aniline or other types. For a brief explanation about fugitive inks, please see Chris’ comments in his Author’s Perspective section early in this article. For more detailed information, including a preliminary list of stamps known to have been printed with fugitive inks, please see the resource thread on TSF [11]. Since fugitive inks were not used as test specimens in this study, that is another area for future work, and Stan is already looking into it.
Parting Thoughts (Mainly from Stan, but agreed by Chris)
Initially, our general thinking was that extended soaking in hydrogen peroxide would ultimately damage the printed image(s) on the stamp(s). We were both quite surprised when the main negative consequence of prolonged soaking in 3% peroxide was that the paper started to break down, with little, if no visible change in the printed image at all.
Additionally, while soaking in hydrogen peroxide seems like a virtual guarantee of improvement in the brightness of the color in almost all classic era stamps, a 10-minute soak is clearly safe, and it is useful for removing many types of stains, in addition to its known use for reversing the effects of sulfuretting. This study did not include a water soak with a mild detergent to remove oils and surface dirt prior to soaking in 3% peroxide, but based on available information, we believe that the results of hydrogen peroxide use have the potential to be further improved if oils and other organics have been eliminated or reduced prior to soaking the stamps in 3% hydrogen peroxide.
Endnotes
- United States Pharmacopeia (USP) What the Letters “USP” Mean on the Label of Your Medicine. Posted on 17-Dec-2015, accessed on 26-Aug-2023. https://qualitymatters.usp.org/what-letters-usp-mean-label-your-medicine
- Helmenstine, Anne Marie. Hydrogen Peroxide Shelf Life: Learn to Test Whether the Liquid is Still Good and to Extend Its Life. Thought Co. website, updated on 07-Apr-2020, accessed on 26-Aug- 2023. https://www.thoughtco.com/hydrogen-peroxide-shelf-life-3975974
- Jackson, Jim (posting as @jkjblue). Cape of Good Hope: Triangular Issues, 1853-1864. The Stamp Forum (TSF) website. Post made on 06-Apr-2022, accessed on 26-Aug-2023. https://thestampforum.boards.net/post/140908/thread
- Dorn, “Cape of Good Hope Triangles: The 4-Pence Blue De La Rue Issues, 1863- 1864”. Cape & Natal Philatelic Journal (CNPJ), Vol. 26, No. 3 (103), September 2022. https://www.capenatalstamps.com/
- Stevenson, Alan. The Triangular Stamps of Cape of Good Hope. H.R. Harmer Ltd., London, 1950.
- Dorn, “Cape of Good Hope Triangles: The 4-Pence Blue De La Rue Issues, 1863- 1864”. Cape & Natal Philatelic Journal (CNPJ), Vol. 26, No. 3 (103), September 2022. https://www.capenatalstamps.com/
- Helgesen, Torbjørn (posting as @tobben63). Whatcha Been Stamping? The Stamp Forum (TSF) website. Post made on 16-Aug-2023, accessed on 27-Aug-2023. https://thestampforum.boards.net/post/173266/thread
- Helgesen, Torbjørn (posting as The Stamp Cave). Cleaning Valuable Norwegian WWII Stamps. YouTube website video, posted in Aug-2022, accessed on 27-Aug-2023. https://www.youtube.com/watch?v=jEu30uFZ1kQ&t=13s
- Brown, Stanley (posting as @stainlessb). Mildew. The Stamp Forum (TSF) Post made on 18-Jan-2023, accessed on 27-Aug-2023. https://thestampforum.boards.net/post/160516/thread
- Flowater How Much Chlorine is in Tap Water? Posted 08-Nov-2021, accessed on 26-Aug-2023. https://home.drinkflowater.com/blogs/posts/how-much-chlorine-is-in-tap-water
- Dorn, Christopher (posting as @berylliumguy). Online Resource: Stamps with Fugitive Inks. The Stamp Forum (TSF) Thread created on 22-Feb-2022, last updated on 16-Aug-2023, and accessed on 27-Aug-2023. https://thestampforum.boards.net/thread/9051/online-resource-stamps-fugitive-inks
###