The Hidden Dangers Lurking in Your Stamp Collection: Plastic Mounts and Sulfur Damage
Keeping your stamp collection in top shape isn’t just about avoiding tears and creases—it’s also about protecting them from hidden chemical damage. One of the biggest threats comes from something meant to keep them safe: plastic mounts. Many of these mounts contain PVC (polyvinyl chloride) plasticizers, which break down over time and release harmful substances, including sulfur. This chemical reaction can seriously mess with your stamps' colors and condition if left unchecked.
How Plastic Mounts Can Harm Stamps
As plastic mounts degrade, they release sulfur, which reacts with oxygen to form sulfur dioxide (SO₂)—the same stuff found in air pollution and acid rain. If moisture gets involved, this can turn into sulfuric acid (H₂SO₄), and that’s where the real trouble starts.
Sulfuric acid can cause your stamps’ colors to change:
Orange stamps might turn brown.
Blue stamps can darken unnaturally.
Red (Carmine) stamps turn dark and are sometimes mistaken for the premium Lake shade.
These changes range from slightly fixable to completely permanent. The longer your stamps sit in deteriorating plastic, the more damage they take—eventually, the paper can become brittle, making them impossible to save.
No Plastic Lasts Forever—Time to Replace Those Mounts
Even high-quality plastic isn’t permanent. Over time, mounts that contain plasticizers will start breaking down and releasing sulfur. That’s why some collectors replace their plastic mounts and stock pages every 10 years or so. Swapping them out regularly helps prevent harmful chemicals from creeping onto your stamps and keeps your collection in great shape.
Choosing the Right Storage Materials
To keep your stamps safe, be picky about your storage materials. Here’s what to look for:
Archival-quality, acid-free products – Use mounts and albums labeled “archival safe” or “acid-free” to avoid harmful chemicals.
Glassine envelopes – These aren’t completely airtight, but they’re a safer, chemically neutral alternative.
Avoid PVC-based plastics – Instead, go for polyester (like Mylar), which doesn’t break down and release damaging substances.
Controlling Temperature & Humidity
Even if you’ve got the right materials, the environment plays a huge role in keeping your stamps safe. Here’s what you can do:
Keep stamps in a climate-controlled space – Aim for 72°F with low humidity. Heat speeds up plastic breakdown, and moisture can cause stamps to curl or stick together.
Fight humidity – If you live in a humid area, consider using a dehumidifier or storing your collection in a controlled environment.
Watch out for air pollutants – Sulfur dioxide can also come from outside sources like industrial pollution or gypsum-based products like drywall and stucco. Keep your collection in a clean, ventilated and dry place away from those materials.
Finding Sulfurized Bargains
I was chatting with some friends at PSE (Professional Stamp Experts), including Caj and a few others, about sulfurized stamps. The topic drifted to stamp restoration, and they shared some pretty amazing stories. If you caught the Stamp Show Here Today podcast from early April of 2025, we talked about a great find by Mark Leon. He picked up a sulfurized U.S. Scott 558 that had originally been graded Extremely Fine 90 by PSE. After carefully restoring it, he managed to get it regraded at a perfect Gem 100—talk about a transformation!
Off the podcast, Caj told me about another cool case—he worked on a U.S. Scott No. 1 that had an unrecognized color variation. After some careful treatment, he brought back its original, sought-after orange-brown shade. Just goes to show, a little knowledge in restoration can go a long way—turning a $500 stamp into a $2,000 one isn’t too shabby!
The Damage You Don’t See—Until It’s Too Late
Many collectors think their stamps are safe in traditional plastic mounts, only to realize years later that chemical reactions have permanently altered their appearance. By staying on top of storage conditions and replacing questionable plastic mounts, you can protect your collection for the long haul.
Stamp collecting isn’t just about finding rare and beautiful pieces—it’s about preserving history. Taking a little extra time to store them properly now ensures that your collection stays vibrant and valuable for generations to come.
