All watermarks are illustrated in the catalogue and appear ahead of each listing. The exception is the standard watermark used for many of the aerograms of Great Britain and British Colonies, as well as for a few other countries; such as, Ethiopia, India, Liberia, etc. This standard watermark is the exclusive manufacture of Messrs. Wiggins Teape & Co. Ltd. of London, England, and reads, "IMPERIAL AIR MAIL" with a picture of a Gateway (Castle) and a capital letter. This capital letter is usually found below the Gateway and above "AIR MAIL" in the design and indicates the year of manufacture of the paper in accordance with the following code of identification:
| A = 1948 | M = 1959 |
| B = 1949 | O = 1960 |
| C = 1950 | P = 1961 |
| D = 1951 | S = 1962 |
| E = 1952 | T = 1963 |
| F = 1953 (reversed) | V = 1964 |
| G = 1954 (reversed) | Y = 1965 |
| H = 1955 | Z = 1966 |
| I = 1956 | A = 1967 (letter below "AIRMAIL") |
| K = 1957 | B = 1968 |
| L = 1958 | C = 1969 |
NOTE: The letters "F" and "G" are always reversed as shown above to avoid confusion with the letters "E" and "C." The letter "J" was never used and the use of the letter "N" has been omitted. The letters "Q", "R", "U" and "X" were also never used. In 1967, the alphabet was repeated beginning with the letter "A". In order to distinguish this second use from the first, the letter was moved and is now below the words "AIR MAIL" at the bottom of the watermark.
The capital letter is an integral part of the design incorporated on the dandy roll which creates the entire watermark in one operation.
The capital letter "L" is known to exist in the normal position, below the Gateway, as well as directly below the letter "I" of "Imperial." The positioning of this letter is varied on occasions by the manufacturer.
The management of the New York office of Wiggins Teape & Co. Ltd. has been most helpful to the editors of this catalogue and has explained to us the following basic facts:
In the manufacture of paper, the watermark is impressed upon the still wet and pulpy paper by a so-called "dandy roll" before the final drying process begins, hence the expression "watermark." At this stage the paper is still quite thick and pulpy. After this impression, or better said "displacement" is made, the paper travels over a great many steam heated cylinders. In forming and drying some sheet distortion takes place and the design created by the devices on the dandy roll, in the wet web of paper, tends to become elongated. In order to correct this condition, the device is purposely deformed so any changes which may occur then result in the design appearing in the finished paper as initially required.
Dependent on the size of sheet to be cut from the finished roll of paper it is sometimes necessary to watermark the paper with the device falling in the machine direction and at other times in the cross direction. Although it is the paper maker's aim in either case to finally achieve similar watermarks, slight variations may be found.
DANDY ROLL: We wish to explain within the limitation of this short space what a dandy roll is and how the watermark design is created.
The original design in its somewhat deformed state is made by a highly skilled artesan and formed by hand out of copper wire. The finished design, made out of this copper wire, is impressed upon wax and then removed, leaving an exact negative impression. The wax is then covered with a thin film of graphite to make it conductive to electricity. It is then immersed in a copper sulphate both and an electric current deposits metallic copper on the graphite surface. Thus electros are made which, of course, have the same form and thickness as the original copper wire design. These electros are then carefully soldered upon the dandy roll.
The dandy roll itself is made of metal and fashioned somewhat like a hollow tube, consisting of an outer cylinder of wire mesh, reinforced at intervals by a skeleton or frame.
It is upon this wire mesh that the electros are soldered at specifically determined intervals across the length of the roll. Spacing between these electros depends upon the size of and the desired registration of the watermark.
It is known that in very rare cases parts of the devices may have become detached from the dandy roll during the manufacturing process, which results in an omission in the watermark. Only three such instances are known, listed under Great Britain, Cat. No. 7b, and Hong Kong No. 3b and 9b, where the capital letter signifying the year of manufacture is missing.
Messrs. Wiggins Teape & Co. Ltd. graciously furnished us with original "rubbings" made directly from the two types of dandy rolls employed. We are illustrating these original "rubbings" as well as the final design as it emerges from the paper making machine and as it appears on the aerograms themselves..
Illustration A: This is the original design when placed to fall in the machine direction. It is shorter in height than the watermark in the finished paper.
Illustration B: This is the original design when placed to fall in the cross direction. It is narrower in width than the watermark in the finished paper.
Illustration C: This illustration is made directly from the finished paper.
NOTE: Allowances in the size and shape of the watermark in the finished paper will have to be considered because of uneven shrinkage and other causes.
The letter "B" has been drawn in in all illustrations for the sake of uniformity.
"KENT VALE PARCHMENT-W 2", mode in 1942, used in 1944 for Southern Rhodesia No. 1.
"KENT VALE PARCHMENT-7", made in 1947, used in 1947 for Southern Rhodesia No. 3.
This same concern, Charles Morgan & Co. Ltd., also supplied the paper used for the aerograms of Ethiopia, watermarked:
"WROTHAM VELLUM WOVE-KENT-A", made in 1948 and used in 1951 for Ethiopia No. 2.
UNWATERMARKED SHEETS: The majority of all aerograms are printed on paper without any watermark, but even among sheets which normally are watermarked, there is found occasionally a sheet entirely without any watermark. This occurs in the die cutting of the individual sheet and is dependent upon how closely the watermark is spaced on the original paper. If widely spaced, more unwatermarked sheets are found. These, when known, are listed as a minor variety.
INVERTED WATERMARKS: A watermark cannot be inverted, as it is the first marking the paper receives. Only the printing can be inverted or sideways. Because there are numerous possibilities in the position of the watermark in relation to the printing, we have made no attempt to list or even verify them.
DEFECTIVE MARKS: Only one such case came to our attention, where the letter "P" of "Imperial Air Mail" is considerably indented. It is a constant variety and occurs on sheets of Hong Kong.
GREAT BRITAIN WATERMARKS: All aerograms printed on blue paper and bearing Tablet B-l are normally watermarked, whether they were issued for Great Britain or any of the Colonies. Of all aerograms of Great Britain proper, this watermarked blue paper exists only with Tablet B-1. All other aerograms of Great Britain With other tablets are unwatermarked.