The Challenge of Classic US Watermarks and Printing Families

For collectors of classic United States stamps, two identical-looking issues can represent entirely different production eras. A stamp's design might remain unchanged for years, yet its underlying paper and printing method can vary significantly. To properly classify these issues, philatelists must analyze both the printing family and the presence of security watermarks.

By understanding how these elements interact, you can safely identify your stamps and document them accurately. Using tools like StampSnap can help you organize these findings and maintain a likely identification record of your collection.

The Four Major Printing Families in Philately

According to the American Philatelic Society, there are four major families used for postage stamps: line-engraved intaglio, gravure, letterpress, and lithography. Distinguishing these families requires looking at how ink is transferred to the paper. Line-engraved intaglio transfers ink from deliberately incised lines, creating a design normally constructed from lines, hatching, cross-hatching, and stippling.

In contrast, gravure is another recess process but forms tone from screened cells. Letterpress relies on raised surfaces, while lithography is a planographic process where the image is formed on a smooth surface. On some modern stamps, more than one process may actually appear.

Examining Printing Methods Safely

When analyzing a stamp's printing method, collectors must treat visual features as cumulative clues rather than definitive proof. To protect the stamp from physical contact, use only non-contact magnification with diffuse or oblique light. Under oblique light, line-engraved intaglio stamps may show raised ink, and the pressure of the printing process may leave debossing on the reverse. However, these are supporting features rather than single tests.

For offset lithography, oil-based ink adheres to the image area, and a rubber blanket offsets that image to the paper. While modern lithography can be sharp, soft or blurred edges are not a dependable identifying rule. Furthermore, a dot pattern must be interpreted with other evidence because gravure and other processes can also show screened structures under magnification. Never diagnose a process from dots or softness alone; always combine observations and consult production records.

The History of USPS Watermarks

Watermarks are a security measure incorporated in stamp paper to deter counterfeiting. These words, letters, or symbols are formed from dies attached to the frame used to make paper from pulp, resulting in thin places in the paper. Some postage stamps exist both on unwatermarked and watermarked paper, and even on paper with different watermarks.

Stamps with the same design but that differ based on the absence or existence of a watermark, or the specific watermark design, generally receive separate catalog numbers. For United States philatelic material, watermarks include the letters USPS on postage stamps, USPOD, USA, and various monograms and numbers on postal stationery, and USIR on revenue stamps.

Distinguishing Double-Line and Single-Line USPS Watermarks

When working with U.S. stamps issued between 1895 and 1916, distinguishing the style of the USPS watermark is critical. A double line USPS watermark was used on U.S. postage stamps from 1895 to 1910, which is classified as Scott watermark 191. Following this period, a single line USPS watermark, classified as Scott watermark 190, was used from 1910 to 1916.

Many stamps include only a portion of the watermark, sometimes only a small part of a single letter. 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 can be particularly difficult to see.

Safe Watermark Detection Methods

To safely detect these faint paper variations, collectors should follow a methodical process. The best method of detecting watermarks is to lay the stamp face down in a dark tray and moisten the stamp with watermark fluid, which brings up the watermark in dark lines against a lighter background. While many collectors use lighter fluid for watermarking, the American Philatelic Society recommends commercial watermark fluid.

Watermark fluid evaporates quickly and should not impact the gum on an unused stamp. The APS helped develop and uses Clarity watermarking fluid, which is safer for your stamps and health than many other options. Other equipment, such as the Safe Signoscope and Morley Bright Watermark Detector, can assist in watermark identification, but traditional watermark fluid remains highly effective. Additionally, dipping stamps in watermark fluid allows collectors to look for thins, creases, and other paper faults.

Organizing Your Findings

Once you have combined your observations of the printing family and the watermark structure, you can confidently classify your stamp. Because watermarks may be the sole difference between a very common stamp and a stamp valued in the hundreds or thousands of dollars, careful documentation is essential.

You can use StampSnap to log your findings, keep track of different watermark varieties, and build a reliable collection record. Always remember to cross-reference your visual clues with official production records to ensure a highly accurate classification.

Frequently asked questions

What is the difference between a double-line and a single-line USPS watermark?

A double line USPS watermark (Scott watermark 191) was used on U.S. postage stamps from 1895 to 1910, while a single line USPS watermark (Scott watermark 190) was used from 1910 to 1916. The single line watermark can be particularly difficult to see and often shows only a small portion of a letter.

How do I safely detect a watermark on a classic stamp?

Lay the stamp face down in a dark tray and moisten it with commercial watermark fluid, such as Clarity. This fluid evaporates quickly, does not impact the gum on unused stamps, and brings up the watermark in dark lines against a lighter background.

Can I identify a stamp's printing method by looking at dots alone?

No. Visual features should be treated as cumulative clues. You should never diagnose a printing process from dots or softness alone, as both gravure and offset lithography can show screened structures under magnification. Always combine your observations with production records.

What are the four major printing families used for postage stamps?

According to the American Philatelic Society, the four major printing families are line-engraved intaglio, gravure, letterpress, and lithography. More than one process may appear on a modern stamp.