Introduction to the Four Major Printing Families
Postage stamp production relies on a few classic printing methods. The American Philatelic Society identifies four major families used for postage stamps: line-engraved intaglio, gravure, letterpress, and lithography. While recess methods like intaglio and planographic methods like lithography are highly common, letterpress (also known as relief printing) represents a distinct, historically significant category that requires careful observation to identify correctly.
Understanding how to distinguish letterpress from other printing methods is an essential skill for any serious collector. Because more than one process may appear on a modern stamp, relying on a single visual test can lead to misidentification. By analyzing cumulative clues under safe, non-contact magnification, you can accurately determine the printing family of your stamps and log them into your StampSnap collection records.
Understanding the Letterpress (Relief) Process
Letterpress is a relief printing method, which means the image areas are raised above the non-image areas on the printing plate. Ink is applied directly to these raised surfaces, which are then pressed against the paper. This mechanical action is the exact opposite of recess printing methods like line-engraved intaglio, where ink is transferred from deliberately incised lines below the plate surface.
Because the inked design on a letterpress plate is pressed firmly into the paper, it often leaves a slight indentation on the front of the stamp and a corresponding raised area on the reverse. This physical impression is a key characteristic of relief printing. However, because paper thickness, printing pressure, and wear vary, collectors must look for multiple cumulative clues rather than relying on a single physical trait.
Distinguishing Letterpress from Line-Engraved Intaglio
To separate letterpress from line-engraved intaglio, collectors should examine the ink and paper texture under oblique light. Line-engraved intaglio transfers ink from incised lines, and its design is normally constructed from lines, hatching, cross-hatching, and stippling. Under magnification and oblique light, raised ink can sometimes be seen on the surface of an intaglio stamp, while the pressure of the recess process may leave debossing on the reverse.
In contrast, letterpress stamps feature ink that is pressed flat or slightly squeezed toward the outer edges of the design lines. This "ink squeeze" often creates a darker, slightly raised border around the printed areas, leaving the center of the lines slightly lighter. While intaglio stamps show raised ridges of ink, letterpress stamps show flat or slightly indented ink surfaces.
Distinguishing Letterpress from Gravure
Gravure is another recess process, but unlike line-engraved intaglio, it forms tone from screened cells. Under magnification, gravure prints display a characteristic honeycomb or grid-like pattern of tiny cells. Because screened or raised effects can also appear in other processes, collectors should combine observations and consult production records rather than diagnosing a process from dots alone.
Letterpress designs generally feature solid, continuous lines of color rather than screened structures. However, some modern letterpress or hybrid stamps may incorporate screened elements for shading. To avoid confusion, always use non-contact magnification with diffuse light to inspect the edges of the design. If the edges are solid and show signs of relief pressure, you are likely looking at a letterpress or relief-printed stamp.
Distinguishing Letterpress from Planographic Lithography
Offset lithography is a planographic process, meaning the image is formed on a smooth surface rather than cut, etched, or raised on a plate. Oil-based ink adheres to the image area, and a rubber blanket transfers, or offsets, that image to the paper. Because there is no physical depth or height on a planographic plate, lithographic stamps are completely flat to the touch and show no debossing or relief indentation on either side.
Modern stamp lithography commonly combines separate process-color layers made from very fine dots. While modern lithography can be sharp, meaning soft or blurred edges are not a dependable identifying rule, it will never exhibit the physical paper distortion or ink squeeze characteristic of letterpress. A dot pattern must always be interpreted with other evidence because gravure and other processes can also show screened structures under magnification.
Safe Examination Workflows for Collectors
When examining your stamps to identify their printing methods, safety should always be your top priority. Never apply heavy pressure, use household solvents, or handle valuable stamps without appropriate tools like stamp tongs. To inspect the surface texture and look for relief indentations or raised ink, place the stamp on a clean, dark surface and use non-contact magnification under oblique (side-angled) light.
If you need to check for paper faults, thins, or watermarks to confirm a stamp's catalog variety, lay the stamp face down in a dark tray and moisten it with a safe, commercial watermark fluid like Clarity. This fluid evaporates quickly and will not impact the gum on an unused stamp. Once you have gathered your cumulative clues—including printing characteristics, paper texture, and watermark details—you can use StampSnap to help create a likely identification and organize your collection safely.
Frequently asked questions
What is the main difference between letterpress and intaglio printing?
Letterpress is a relief process where ink is transferred from raised surfaces, often leaving a slight indentation on the paper. Line-engraved intaglio is a recess process where ink is transferred from incised lines, often leaving raised ink on the stamp surface and debossing on the reverse.
Can I identify a printing process based solely on the presence of dots?
No. Screened structures and dot patterns can appear in multiple processes, including gravure, offset lithography, and certain hybrid methods. Collectors should combine visual observations with official production records to make an accurate determination.
Why is oblique light useful when identifying stamp printing methods?
Oblique, or side-angled, light casts tiny shadows across the stamp's surface. This makes it much easier to detect physical characteristics like the raised ink of intaglio, the flat surface of lithography, or the slight relief indentations of letterpress without touching the stamp.
How does offset lithography differ from letterpress?
Offset lithography is a planographic process where the image is printed from a flat surface using a rubber blanket, resulting in a completely flat ink layer. Letterpress is a relief process that presses ink into the paper, often creating slight indentations and a characteristic "ink squeeze" effect along the edges of the design.