Postage stamp paper is the foundation or substrate of the postage stamp to which the ink for the stamp’s design is applied to one side and the adhesive is applied to the other. The paper is not only the foundation of the stamp but it has also been incorporated into the stamp’s design, has provided security against fraud and has aided in the automation of the postal delivery system.
Stamp catalogs like Scott’s Standard Postage Stamp Catalog (SC) often document the paper the stamp is printed on to describe a stamp’s classification. The same stamp design can appear on several kinds of paper. Stamp collectors and philatelists understand that a stamp’s paper not only defines a unique stamp but could also mean the difference between an inexpensive stamp from one that is rare and worth more than its common counterpart.
Making an accurate determination of the stamp’s paper may require special tools such as a micrometer to measure the thickness of a stamp, certain fluid chemicals to reveal hidden features, magnifying glasses or loupes to see fine details, digital microscopes to examine the minutest details of the paper or ultraviolet light to illuminate the paper to reveal its glowing aspects. Certain paper types may require the services of an expert as the only sure way of knowing the true identity of the stamp’s paper.
All paper is endowed with certain characteristics by its maker. Depending on the purpose of the paper, the craftsman will choose specific materials and apply certain manufacturing processes to achieve the design objectives. Characteristics such as composition, weight, color, size, watermark, surface finish, opacity, hardness and strength all have to be established before the papermaker can begin his work.
The making of paper can be broken down into three phases; the preparing of the pulp into a suspension of fibers; the forming of the paper on a mould or an endless wire mesh; and lastly the finishing of the paper’s surface and drying. From a philatelic interest, it is the second phase, the forming of the paper that yields the most interesting characteristics.
In the first phase of papermaking the characteristics such as its composition, color and weight is determined. Paper has as its chief component, a mat of cellulose fibers. Cellulose is the skeleton structure of plant cells and can be separated from the plant for use in paper. Cellulose has several characteristics that make it desirable for paper, the foremost being its strength when formed into a mat or web. When cellulose fibers come in contact with each other in water, a bond is formed. When water is removed from the adjoining fibers, the bond between the fibers strengthens. Pulp, the collection of individual fibers, may be bleached, especially if the paper is to be dyed a different color or the paper is expected to be white. Since most paper is either printed or written upon, fillers are added to the pulp to fill the pores of the paper and sizing is added to make the fibers water resistant, yet both act as fillers. Unsized paper is blotting paper, making it unsuitable for printing. Fillers and sizing are added to the pulp to absorb the ink quickly, unlike pure cellulose. Fillers can be glues made from animal products, starches from rice or wheat, resins or gums, or minerals such as calcium carbonate, titanium dioxide or kaolin. Mineral fillers are the most common as they are very effective as a filler. When all of these ingredients are assembled, they are suspended in water, which may include a color dye, as the furnish to the second phase of papermaking.
The paper is formed in the second stage of papermaking. With handmade paper, the furnish is stored in a vat and the craftsman uses a mould to strain out enough material to form a sheet of paper. The mould determines the dimensions of the finished sheet and its weight, which ultimately establishes the paper’s thickness. The mould is usually a wire mesh that acts as a strainer such that the furnish is separated out of the water. The water drains off, leaving layers upon layers of fibers or a web of paper on the mould. The texture of the paper is determined by the nature of the mould. Wove paper has a uniform texture while laid paper has a fine-lined texture created by wires that are attached to the wire mesh. If a watermark is part of the paper’s design, it is the mould that creates the watermark, in the same way that the fine lines of laid paper are created. A watermark is a deliberate thinning of the paper by the placing of either wires or metal shapes, called bits, onto the wire mesh of the mould. When the mould is removed from the vat, the water drains causing the pulp to be deposited more between the wires or bits relative to the top of the bits or wires. When the dried paper is held up to a light, the thinner paper will appear lighter in contrast to the thicker paper, thus creating a watermark. Numerous countries have used a variety of designs for their watermarks as a means to prevent forgery of stamps, making the watermark of particular philatelic interest.
In comparison, machine-made paper is made on the Fourdrinier machine by drawing the furnish out of a vat onto an endless wire mesh. The paper, shortly after being drawn from the vat, is usually pressed with a Dandy roll as the mechanism to imprint a watermark onto the paper. Machine-made paper can produce single sheets of paper or one large continuous web of paper that is collected to form large rolls.
One characteristic of machine-made paper is that it creates a direction or an alignment of the fibers, which directly impacts its strength. This is of particular importance when tearing the paper, as one would do to separate a stamp for use. When the tear is aligned with the direction of the fibers, the paper will tear evenly. When the tear is opposed to the direction of the fibers, the paper will tear unevenly, in a jagged line. Handmade paper disperses the fibers in unpredictable directions and therefore yields a paper with the most overall strength. A paper’s strength had an influence on the separation methods used for a stamp. For example, a stronger paper may have needed a higher number of perforations per inch to best facilitate the separation of the stamps. Similarly, many stamps have two different standards of perforation for its length and width to optimize the ease of separation while minimizing the cost of manufacturing.
In the last stage of papermaking, the paper is finished and dried. The finishing of the paper can include the application of a coating that will produce the best effects when printed upon. The coating is a fine layer of special sizing applied to one or both sides of the paper to fill in all of the pores and to smooth out the surface of the paper. A glossy appearance often is a characteristic of coated paper. Once the coating is applied, the paper making process is complete.
Certain postage stamps have been printed on security paper, which is paper that has additional characteristics coated or printed onto the paper to prevent the reuse of the postage stamp and as a means to prevent forgery.