Watermark

A watermark is a pattern or design formed in stamp paper during its manufacture. Unlike a printed overprint or design element, a watermark is integral to the paper itself: it is created by thinning the paper pulp at specific points during the production process, so that when the paper is held up to light — or treated with watermark detection fluid — the design becomes visible as a lighter area against the surrounding sheet. Watermarks have been used in stamp paper since the earliest days of adhesive postage stamps, serving both as a security feature and as a way to track paper batches and printing runs.

How Watermarks Are Made

During papermaking, a wire mesh cylinder called a “dandy roll” presses against the wet paper pulp before it sets. The dandy roll carries a raised wire design; where the design contacts the pulp it displaces some fibres, creating a thinner area. When dry, these thinner areas transmit more light, making the pattern visible by transmitted illumination. The process is the same as watermarks in banknotes and high-security documents.

Why Watermarks Exist

Watermarks serve two main purposes for postal authorities. First, they authenticate the paper: forgers who might print stamps on plain paper could not easily replicate a watermark embedded in the pulp. Second, they allow postal administrations to track production: different watermark designs were used for different printing contracts, enabling authorities to identify which stamps came from which paper supply — useful both administratively and for investigating fraud.

Detecting Watermarks

Watermark fluid (benzine or commercially prepared watermark fluid such as Instanta) is the traditional method. A few drops placed on the back of the stamp in a black watermark tray cause the paper to become temporarily translucent, revealing the watermark design. The fluid evaporates completely without damaging the stamp or its gum if used carefully. Never use water, as it will damage gum and may cause toning.

Detector boxes and backlighting (such as the Morley-Bright Detectamark) illuminate the stamp from below, allowing watermarks to be seen without applying any fluid. These are preferable for mint stamps where preserving gum is important.

Digital scanning with image-processing software can reveal subtle watermarks that are difficult to see by eye. This is increasingly used in expertisation.

Common Watermark Patterns

British stamps used a range of watermarks across different reigns. Victorian issues used patterns such as the Large Crown and Small Crown; later issues used the Multiple Crown watermark (a pattern of small crowns and letters repeating across the sheet). Commonwealth countries such as Australia, Canada, and India used related crown watermarks supplied through the Crown Agents paper supply system.

United States stamps used the “USPS” single-line watermark on issues from 1895 to 1910 and briefly later, though most modern US stamps are unwatermarked.

Watermark Orientation

A stamp’s watermark can appear in different orientations relative to the stamp design, and this matters for identification. The standard orientations are: upright (watermark reads correctly when stamp is face up), inverted (watermark is upside down), reversed (watermark is mirror-image), and inverted and reversed (both flipped). Stamps with inverted watermarks are often listed as separate, scarcer varieties in catalogues — an inverted watermark results from a sheet of paper being fed into the printing press the wrong way round, which happened occasionally during production.

Impact on Value

Watermark varieties significantly affect stamp value. The 1861–67 US issues exist in both watermarked and unwatermarked versions, as do many classic British Commonwealth stamps. Misidentification of a watermark — or failure to check for one — is one of the most common errors made by collectors purchasing classic material. A stamp that appears identical on its face may be a common variety or a major rarity depending solely on its watermark.