Machins & Wildings Definitive Stamp Issues

B1 phosphor ink (green afterglow)
B1 phosphor ink was first developed in 1959 for use on the Wilding issues, but in 1972 the phosphor was incorrectly applied to a 2½p centre band (cylinder 10).

 
 The 2½p FCP/PVA centre band stamp issued in error with green phosphorescence (B1 phosphor)

B3 phosphor ink (Short wave reaction except Jet variety which is short and long wave)
Since the introduction of the B3 phosphor in 1965, phosphor has remained in a general classification colour of violet.  Impurities have occurred to the phosphor, such as the ‘Jet’ variety (named after its discoverer J. E. Thompson). ‘Jet’ phosphor is contaminated with a yellowing agent which also causes the phosphor to phosphoresce under long wave.

 
B3 phosphor

SA Phosphor ink (Short wave reaction only)
Sulphanilic acid was used for stamps printed litho as it was less prone to be affected by moisture.

 
SA phosphor (Litho printed stamps only)

A phosphor ink (Short wave reaction only)
The ' A' type phosphor, also referred to  by collectors as ‘new phosphor ink’ was introduced in July 1986. This ink emits a brief afterglow and some of the band variations are difficult to determine.

 
'A type' phosphor (New phosphor ink)

C phosphor/yellow fluor (Short wave reaction only)
In 1991 Enschedé introduced a phosphor/fluor mixture. This was the ‘A’ type phosphor mixed with a yellow fluor agent known as Cartax, the ink became known to collectors as 'C type phosphor'. The original C phosphor emits a bright yellow glow under ultra violet light and is denoted in the stamp lists as 'AY fluor'. Enschedé also issued weaker yellow fluor mixtures over the following years, these vary from yellowish green to greenish yellow under ultra violet and are described in the lists as 'AY2 fluor' (yellowish green) or 'AY3 fluor' (greenish yellow).

The above images represent the fluorescence of the AY phosphor inks as viewed under long wave, although the AY phosphor inks will not phosphoresce under long wave it is the easiest way to identify them. If viewed under short wave the face is brighter and the phosphor bands are pale yellow.

B phosphor/blue fluor (Short wave reaction only)
This ink is a modification of the of the original ‘C’ type phosphor. The blue fluor replaced the yellow after changes were made to the Post Office’s coding detection system, there are varying shades of the blue fluor but seem to come in a general classification of: Dull blue-violet (mainly Questa and Walsall stamps printed lithography).  Blue fluor stamps printed litho are easier to identify under long wave light  Deep blue-violet (mainly Enschedé, Questa and Walsall stamps printed photogravure/E.M.E). Bright blue (mainly De La Rue stamps printed photogravure/E.M.E).

The above is only a guide to assist identification of individual printers blue phosphor inks.

 
 B phosphor/blue fluor (De La Rue print)

The above image represents the fluorescence of 'B phosphor ink' as viewed under long wave, although the 'B' phosphor ink will not phosphoresce under long wave it is the easiest way to differentiate between the different printers phosphor inks. If viewed under short wave the face is brighter and the phosphor bands are pale blue.

A2Y phosphor (Novaglo)/yellow fluor (Short and long wave reaction )
The 1994 Enschedé 38p rosine was the only value issued with the A2 phosphor/yellow fluor combination, the yellow fluor was superceded by blue before any other values were released.

 
 A2Y phosphor (Novaglo)/yellow (2mm varnished bands)

The above image represents the fluorescence of A2Y phosphor ink as viewed under long wave, this phosphor will also phosphoresce under long wave. If viewed under short wave the face is brighter and the phosphor bands are pale yellow.

A2B phosphor (Novaglo)/blue fluor short and long wave reaction (Questa/Walsall litho stamps only)
A number of booklet panes printed litho by Questa and Walsall were issued with the A2B phosphor and emit long and short wave afterglow. This reaction only occurs on a small number of panes and is comparatively  rare, most litho printed panes with blue fluor are 'B' phosphor and only react to short wave, conversely a ll booklet panes printed photogravure by Questa and Walsall are Novaglo and react to short and long wave.

The above images show the fluorescence of 'A2B' phosphor ink under long wave, this phosphor will also phosphoresce under long wave If viewed under short wave the face is brighter and the phosphor bands are dull blue on the photogravure print, but are invisible on the lithographic print..

Varnished bands

Varnished bands were first introduced on the yellow fluor issues. Initially Enschedé had problems with their paper being too absorbent for the phosphor ink and this was affecting the UV signal to the ALF machines. To try and rectify the problem 2mm or 4mm varnished bands were applied down the vertical stamp gutters before applying the phosphor ink.

Copyright (c) 2008 Denis Stevens. All rights reserved