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Graphite lines
Graphite lines were introduced in 1957 as an experiment in automated letter sorting. An automatic letter facing machine (known as ALF) was installed at Southampton, the machine was designed to sort the mail according to the amount of graphite bands counted on the back of the stamp as the letter passed through a scanner. Sheets were printed with black electrically conducting graphite lines on the back prior to being gummed ~ one graphite band on the 2d (the printed paper rate at the time) ~ two bands on the ½d, 1d, 1½d and 2½d values, the stamps were printed on St Edwards crown watermarked paper. There was a second issue printed between 1958 and 1959 using the same values as the first but with the addition of a 4d and 4½d. The second issue was printed on multiple crowns watermarked paper. Graphite band stamps were produced in sheets, coils and booklets. |
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Graphite lines - Phosphor bands
The initial trials of the ALF were not satisfactory and as a consequence experiments were conducted in the use of phosphorescent inks. In November 1959 ALF was operated with the addition of an phosphor scanner. The graphite lined stamps were overprinted on the face with phosphor bands, one phosphor band on the 2d ~ two bands on the ½d, 1d, 1½d and (2d watermark error) on St Edwards crown watermarked paper, phosphor bands were also applied to the 2d, 2½d, 3d, 4d and 4½d values on multiple crowns watermarked paper. The phosphor used in the experiments was commercially known as Lettalite B1 which produced a green phosphorescence when exposed to ultra violet in the 2000 to 3000 Angstrom range. Graphite and phosphor stamps were produced in sheets only, bands are generally 8mm. |
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Lettalite B1 (green afterglow)
The trials of the phosphorescent ink was deemed successful and on the 6 July 1960 ALF was converted to scan phosphor only. On 22 June 1960 the ½d, 1d, 1½d, 2d, 2½d, 3d, 4d and 1/3 values with Lettalite B1 phosphor bands applied were issued, a 6d value followed on 27 June. The stamps were printed on multiple crowns watermarked paper. Green phosphor band stamps were produced in sheets, booklets and coils, bands are generally 8mm (two 4mm bands). |
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Lettalite B2 (blue afterglow)
In 1961 the Lettalite B1 phosphor was replaced by Lettalite B2 which produced a blue phosphorescence when exposed to ultra violet in the 2000 to 4000 Angstrom range. The blue phosphor was in use between 1961 and 1966 ~ ½d to 4½d, 6d and 1/3 values were issued with Lettalite B2 phosphor bands applied. The stamps were printed on multiple crowns watermarked paper. This period also covered the change over to the white paper, plus two postal rate changes, this resulted in the 2d, 2½d and 3d being issued with either one or two phosphor bands applied. Blue phosphor band stamps were produced in sheets, booklets and coils, bands are generally 8mm (two 4mm bands). |
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Lettalite B3 (violet afterglow)
The phosphor was again changed in 1965 to Lettalite B3, this was due to the introduction of address coding and automatic letter sorting at Norwich, a different reacting phosphor was required which would not interfere with letter sorting. Lettalite B3 uses Terephthalic acid as the activator which is inert to ultra violet light in the wavelength of 3650 Angstroms used in the sorting machine but stimulates emission in the visible spectrum when subjected to 2537 Angstroms used in the letter facing machine. 8mm bands were applied to stamps issued in 1965. The values were ½d, 1d, 1½d, 2d, 3d, 4d, 6d and 1/3. The bands were changed to 9.5mm for stamps issued in 1966 - 67, the values were 1d, 2d, 3d, 4d, 5d, 6d, 7d, 8d, 9d, 10d, 1/-, 1/3 and 1/6. The B3 phosphor was used on stamps printed photogravure up until 1986 when Harrison and Sons developed a new phosphor ink (Lettalite B8), known to collectors as 'A' phosphor. Violet phosphor band stamps were produced in sheets, booklets and coils, bands are 4mm, 8mm, or 9.5mm (two 4mm or 4.75mm bands).
Copyright (c) 2008 Denis Stevens. All rights reserved. |
