The Role of Watermarks in Stamp Valuation
Watermarks are a critical security measure incorporated into stamp paper during the manufacturing process to deter counterfeiting. These marks are formed from dies attached to the frame used to make paper from pulp, which results in thin places in the paper. Because some postage stamps exist both on unwatermarked and watermarked paper, or even on paper with entirely different watermarks, identifying these hidden patterns is essential for accurate valuation.
Stamps that share an identical printed design but differ based on the presence, absence, or specific style of a watermark generally receive separate catalog numbers. This subtle physical difference can be the sole factor that distinguishes a very common, low-value stamp from a rare variety that carries a significantly higher catalog value. For collectors, mastering watermark identification is a fundamental step in evaluating any classic philatelic holding.
Key United States Watermark Varieties: USPS, USPOD, and USIR
United States philatelic issues feature several distinct watermark designs that collectors must learn to differentiate. On standard U.S. postage stamps, the letters USPS are the most common watermark. A double-line USPS watermark was used on U.S. postage stamps from 1895 to 1910, designated as Scott watermark 191. This was followed by a single-line USPS watermark, designated as Scott watermark 190, which was used on U.S. stamps from 1910 to 1916.
Beyond standard postage, other branches of U.S. postal and fiscal administration used specialized watermarks. Postal stationery often features USPOD, USA, or various monograms and numbers. Meanwhile, U.S. revenue stamps frequently feature the watermark letters USIR. Identifying these specific letters helps collectors confirm the original purpose and period of the paper, which directly impacts the stamp's catalog classification and market value.
The Challenge of Partial and Hard-to-See Watermarks
One of the primary challenges in valuing watermarked stamps is that the entire watermark is rarely visible on a single stamp. Because the watermark design is spread across the paper sheet, many individual stamps include only a portion of the watermark, sometimes showing only a small part of a single letter. This requires a methodical approach to reconstruct the letters and determine which watermark is present.
Additionally, visibility varies significantly depending on the issue. While watermarks on most U.S. postal stationery can be fairly easy to detect without any special equipment, the single-line watermarks on U.S. stamps from the 1910-1916 period can be particularly difficult to see. Relying solely on a visual inspection under normal light is often inconclusive and can lead to incorrect valuations.
Safe Methods for Detecting Watermarks
To safely reveal these hidden paper details, collectors use specialized techniques. The best method of detecting watermarks is to lay the stamp face down in a dark tray and moisten the stamp with watermark fluid. This process brings up the watermark in dark lines against a lighter background, allowing for clear identification without damaging the stamp.
While some collectors use lighter fluid for watermarking, the American Philatelic Society recommends using commercial watermark fluid. Commercial fluids, such as Clarity watermarking fluid which the APS helped develop, are safer for both your stamps and your health. This fluid evaporates quickly and is formulated so that it should not impact the gum on an unused stamp. Other mechanical devices, such as the Safe Signoscope and the Morley Bright Watermark Detector, have been developed to assist in this process, but traditional watermark fluid remains the preferred choice for many experienced philatelists.
Dipping for Hidden Faults and Structural Integrity
Beyond identifying the watermark letters themselves, placing a stamp in watermark fluid serves another vital role in valuation: detecting physical damage. Stamps are frequently dipped in watermark fluid to look for thins, creases, and other paper faults that are invisible to the naked eye when the stamp is dry.
A stamp with a rare watermark may lose a significant portion of its potential value if it possesses a hidden thin or a crease. By observing how the fluid interacts with the paper fibers, you can spot these structural defects early. This ensures that your valuation is based on the true physical condition of the stamp rather than its face appearance alone.
Documenting Your Findings and Organizing Your Collection
Once you have safely identified the watermark and checked for any paper faults, keeping an organized record is key to managing your collection's value. You can use digital tools like StampSnap to log your findings, create a digital inventory, and keep track of which stamps have been verified. This helps you maintain a clear record of your collection's varieties over time.
Remember that while digital tools like StampSnap can help you organize your collection and suggest likely identifications, physical expertizing using watermark fluid and reference catalogs remains the standard for definitive valuation. By combining careful physical testing with structured digital records, you can confidently build and value your philatelic collection.
Frequently asked questions
What is the difference between double-line and single-line USPS watermarks?
The double-line USPS watermark (Scott watermark 191) was used on U.S. postage stamps from 1895 to 1910, while the single-line USPS watermark (Scott watermark 190) was used from 1910 to 1916. The single-line watermark is generally much more difficult to detect.
What do USPOD and USIR stand for on U.S. stamps?
USPOD stands for the United States Post Office Department and is found on postal stationery. USIR stands for United States Internal Revenue and is found on revenue stamps.
Will watermark fluid damage the gum on an unused stamp?
No, commercial watermark fluids like Clarity are designed to evaporate quickly and should not impact the gum on an unused stamp when used properly.
Why can I only see a small part of a letter on my watermarked stamp?
Because watermark designs are spread across the entire sheet of paper during manufacturing, individual stamps usually only capture a small section or a single portion of a letter from the overall watermark pattern.