If you are an experienced stamp collector, you have probably come across a brown stamp that should actually be orange according to the stamp catalog.

Unfortunately, you have not discovered a printing error that would make the stamp worth thousands of dollars. Instead, what you have is an example of “sulfurization.”

What Is Sulfurization?
Sulfurization is a chemical process that can change the color of stamps containing lead in their ink. It occurs due to the combination of sulfur in the air with the lead in the pigment, which causes the stamp to darken.

This happens mainly with orange stamps issued before 1930, but it can occur with any pigment that contains lead.

This process is often called oxidation, but that is incorrect. Sulfur causes the reaction, not oxygen.

Causes of Sulfurization
So what is the culprit? Let’s start with a common place where people store their stamp collections.

Many gun safes are lined with drywall and then covered with carpeting. This drywall contains sulfur. When postage stamps are stored in a gun safe for long periods of time, sulfurization is likely to occur.

Many older homes also contain sulfur in their drywall. Therefore, simply leaving your stamps exposed in your home for long periods can also cause sulfurization.

Impact on Value
From an appraisal standpoint, sulfurized stamps may be worth less than their well‑preserved counterparts.

Collectors and buyers often prefer stamps in their original, unchanged condition, and sulfurization may be viewed as a form of damage that reduces the stamp’s appeal and market value.

Likewise, a buyer may hesitate to purchase a sulfurized stamp if they are not familiar with the solutions that can restore it.

Fortunately, there is an easy and inexpensive way to restore your sulfurized stamps without damaging them or affecting their original gum in any way.

How to Remove Sulfurization from Stamps
This method is very effective for removing sulfurization from stamps and restoring their original color. More importantly, the process can be performed without damaging the stamp or disturbing its original gum in any way. It is also known as “fumigating” a stamp.

Step 1: Take a glass cup or a small container.

Step 2: Take a paper towel and separate its thickness into two individual sheets by peeling them apart so that you have two single‑ply sheets.

Step 3: Fill the container halfway with hydrogen peroxide. Note that hydrogen peroxide quickly loses its strength after the first opening, so if you do not see results, you may need to open a new bottle.

Step 4: Place one of the paper towel sheets over the top of the cup, put a rubber band around it, and pull it tight so that the surface is flat.

Step 5: Place the stamp face down on the paper towel. Check again after 24 hours.

You should notice a significant difference in the color of the stamp, returning toward its original orange shade. If not, discard the used hydrogen peroxide and repeat steps 3 through 5.

NOTE: The stamp must never come into direct contact with the hydrogen peroxide. This method suspends the stamp safely above the peroxide, resting on the tightened paper towel.

Also make sure there is space around the stamp where the peroxide can evaporate. The stamp may be damaged by moisture if there is not enough room for it to “breathe.”

Preventive Measures
Preventing sulfurization requires careful attention to storage and handling practices. Here are some effective strategies for collectors:

1. Optimal storage: Avoid using gun safes or containers made from materials that may release sulfur compounds. Find a safe that does not contain drywall, or consider removing it.

2. Avoid direct sunlight: Keep your stamps away from direct sunlight. Use storage cases or boxes with UV filtering to protect them from harmful UV rays that can accelerate chemical reactions.

3. Regular inspection: Periodically check your collection for signs of discoloration or damage. Early detection of sulfurization can help you take timely action to prevent further deterioration.

Sulfurization of stamps is a common but preventable phenomenon that poses a challenge for philatelists. By understanding the causes and consequences of sulfurization, you can apply effective preventive measures to protect your stamps.