There are many rewarding aspects of philately that are overlooked by the collector intent on simply filling the spaces in their album. The production and variety of paper and the associated watermarks, the often politically motivated choice of subject and subsequent design stage, the intricate work and tools of the engraver, the production of the dies, reliefs and plates, the machinery used to print the sheets of stamps and the pigments, dyes and inks used - the list goes on - all are valid and equally rewarding studies in their own light. We will concern ourselves here with the production stage - the work of the engraver and the printing methods employed.
The complicated nature of the production process has led to variations in the stamps produced, many of which hold intense interest for philatelists. An understanding of the basic principles that caused these variations is necessary before one begins the study of many U.S. stamps, in particular the one and three cent stamps of the 1851 Issue. We will discuss these factors in upcoming articles.
There are six major methods of printing; all involve transferring an image to a substrate, either directly or indirectly. Gravure, letterpress, flexography, screen printing and digital printing are methods of direct printing. Lithography, the predominant method of printing today, is an offset method of printing, in which the image carrier does not come into direct contact with the substrate, but is passed through an intermediary such as a rubber blanket. Other than digital printing, the image carrier can be one of three types: intaglio, planographic, or relief, depending on the relationship of the design to the non-printed area of the plate. In digital printing the image carrier is an array of photo-receptors.
image carrier: a device that transfers the design to the substrate, that is: "carries" the inked "image" to the substrate
substrate: the material that is to be printed on; this can be as varied as paper, glass, or metal and just about anything that will accept an image transfer
Relief, or typographic, printing has the design raised above the surface of the non-printed area. Think of a typewriter or printer s type, each character is above the non-printing background. This is the oldest method of printing and originally meant cutting away the non-printing areas in a block of wood and later metal to raise the design above the surface of the image carrier. Letterpress, which uses an inflexible plate made of wood or metal (often lead type), and flexography, which uses a flexible plate made of plastic or rubber, are examples of relief printing.
Relief - the image area is raised above the plane
Planographic printing has both the design and the non-printed area in the same plane. The area to be printed is determined by either an electrical or chemical process and is based on the principal that oil-based inks and water do not mix. Offset lithography is a planographic method of printing. Although the quality rarely matches that of intaglio and the process is the most complicated way to print, it is flexible and relatively low cost for medium to large runs and is the predominant method used in commercial printing today.
Planographic - the image area is in the plane
Intaglio, or gravure printing has the design cut below the surface of the non-printing area, either by chemical or physical means. It is in a sense the opposite of relief printing in that the area to be printed is cut below the image carrier. Intaglio is by far the most difficult and time-intensive means of printing, yet the quality of the print is far superior, since the intensity of the printed design is in direct proportion to the depth of the cuts made by the engraver. The art of engraving, cutting the fine lines into the die, is considered by some to be the highest form of craftsmanship an artist may obtain. Although it is possible to obtain an engraving by etching the design into the plate by chemical means, the quality in no way compares with the beauty of a finely hand-tooled design. An engraver who does portrait work must hone his skills for anywhere from 10 to 15 years before he can call himself a craftsman. Even then only one in a hundred has the competency to become a first class portrait engraver. This is why it so difficult to counterfeit U.S. stamps, the level of skill is that great, and this of course is why many governments throughout the world have chosen to print their stamps, securities and paper currency by the line engraved method.
Two metals are often used as the image carrier, copper and steel. Copper is softer and easier to engrave, while the harder steel will allow more delicate work. Although the initial printings from a copper plate may prove indistinguishable from printings from a steel plate, over time the softer copper plate will wear out much more quickly. Artists prefer copper plates for preparing their engravings since plate wear is not an issue on small runs. Engravers of stamps and securities usually use steel plates for the larger runs needed.
The engraver uses a tool called the graver and cuts fine line after fine line to create the design. The progress is exceedingly slow and a casual observer may not note any change in the design over many hours or even days of work. For quality work, the graver must be kept sharp and sharpening the engraving tools is considered an art in itself. Amazingly, the design must be entered in reverse in order that when it is printed it will appear normal. This again is a technique learned only after many long hours of practice.
It is of course possible to directly engrave the design into a steel or copper plate. This may prove practical if the design is not repeated more than a few times. Each design will be slightly different from its neighbor since it is for all practical purposes impossible for an engraver to exactly duplicate his work. It is easy to see how time-consuming engraving, for example, all 200 designs on the early plates used to print U.S. stamps.
Since a plate is for practical purposes a large number of nearly identical designs placed side by side, top to bottom, it made sense to make a die (or dies) that could be used to enter the same design over and over without the need for another engraving. However, if the die were pressed directly into the plate the resulting image would be in normal orientation and when printed would appear to be in reverse (and raised). An intermediate transfer mechanism was needed, namely the transfer roll.
Simply put, the design was engraved on a soft metal die in reverse, hardened and applied to a transfer roll, sometimes multiple times to create a transfer roll with more than one design. While the design on the die is recessed (engraved) and in reverse, the design on the transfer roll is raised (relief) and in normal orientation. Each design on a transfer roll is termed a "relief"; transfer rolls with multiple designs rocked in have multiple reliefs. The transfer roll is then rocked multiple times into the printing plate until the plate is filled with the appropriate number of the design in reverse. The plate is then hardened. Finally, ink is applied to the plate, excess ink in the non-printing areas wiped off, and the inked plate is pressed against dampened paper to create a sheet of engraved stamps in normal orientation with the ink raised above the surface of the paper.
For more information we recommend the following:
Fundamentals of Philately by L. N. and M. Williams - APS Publisher, 1971
Printing Postage Stamps by Line Engraving by James H. Baxter - APS Publisher, 1939
die: a single engraved design, in reverse and cut below the surface of the metal
transfer roll: multiplies the design on the printing plate - each design on the transfer roll is raised and in normal orientation
relief: a single design on the transfer roll