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 Post subject: Phosphor afterglow on Wilding definitives
PostPosted: Thu Apr 23, 2015 10:48 pm 
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Apologies if this has been raised before, but I can find no reference to it.

My query concerns the 'afterglow' on Wildings definitives phosphor issues under the ultra-violet lamp. I seem to recall hearing (or reading) somewhere that the green and blue phosphors give the most prolonged afterglow, the violet fading very rapidly. Can anyone confirm this please ?

Many thanks

Tony


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 Post subject: Re: Phosphor afterglow on Wilding definitives
PostPosted: Wed Sep 09, 2015 12:49 am 
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Finally got an answer on this from a dealer :

Violet phosphor afterglow fades most rapidly, followed by blue, with green taking longest to fade. Hope this may be useful to someone as well as me.

Tony


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 Post subject: Re: Phosphor afterglow on Wilding definitives
PostPosted: Tue Feb 16, 2016 6:54 pm 
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Identifying Green/Blue/Violet Phosphor Colours on Queen Elizabeth II Wilding Definitives
Some of the coloured phosphors can be sorted by normal sight without the use of ultra violet lamps, as follows:
 Phosphor Graphite issues all have Green Phosphor.
 Phosphor issues from the 5d., 7d., 8d., 9d., 10d., 1s. and 1/6 values are all violet phosphor, with 9.5mm. bands.
 4mm. Centre Band issues of the 3d., value are all Violet Phosphor.
 Side Band issues of the 2½d. value are all Blue Phosphor.
 Most 9.5mm. bands are Violet Phosphor. The very few exceptions are from sideways watermark booklet panes of four - reported on the Blue Phosphor ½d. value in particular - and attract high prices because of their scarcity.

Thus all the above groups can be sorted without the use of an ultra violet lamp. Having sorted these they can be used as 'standards' against which to compare other issues when learning the subject.
Having identified the issues that can only come from one of the three colours of phosphor issues, the remaining stamps are then more precisely identified by the use of a short wave ultravioletlamp.
It is important to exclude daylight or artificial light, as the stamps are best examined for the phosphor colours using the u/v lamp in total darkness.
When applying the u/v lamp in close proximity to the stamps, keeping the lamp lit, the phosphor bands will normally be visible as the bright stripes down the stamp, in the normal two band, side band or centre band positions. The brightest reaction comes from the blue phosphor, or from the violet phosphor; green phosphor is also quite bright but a little less so than the other colours.

The most obvious difference between the three colours of phosphor occurs immediately after the lamplight is switched off, whereupon the so-called 'after-glow' of the phosphor remains visible for a short time:
 GREEN PHOSPHOR glows longest, somewhat less brightly than while the lamp is still lit, but importantly the 'after-glow' is clearly green.
 BLUE PHOSPHOR glows almost as long as the Green Phosphor, and is clearly not green, but rather of a bluish tone of greater brightness.
 VIOLET PHOSPHOR shows an after-glow in most cases, but is much shorter than the other two phosphor colours, and indeed in some issues the violet phosphor after-glow dies so quickly after the lamp light is switched off that you almost miss the after-glow altogether. Any after-glow that clearly dies quickly, or instantly, is violet phosphor. Violet phosphor is not clearly 'violet', but rather a short-lived bright glow, clearly not green, but which could be said to be vaguely bluish just as well as violet.


'PHOTO.' Phosphor was applied by the photogravure printing process, for which the printing roller surface was 'photo-etched' with acid. The band printing area is composed of a multitude of diagonal screen lines (150 or 250 to the inch, set diagonally across the bands), and as they are photo-etched they are recessed into the cylinder surface, and are relatively shallow though deep enough to retain ink left from the inking roller; after inking excess ink is removed from the roller by the so-called 'doctor blade', leaving the ink in the screen lines, which is then applied to the stamps in the printing web.

As the 'photo.' screen is shallow there is no impression of 'tram-lines' left by the roller on the printed stamps. However, the portion of the plate which is not etched presses closely on the stamps and 'glazes' the portion of the stamp without phosphor, so this portion of the finished stamps appears slightly glossy when viewed at a very shallow angle to the light (in the manner adopted when looking at phosphor bands by the naked eye in daylight, but setting the stamp at the shallowest angle possible).
Careful examination of the 'photo.' phosphor band, by looking diagonally across the band at a very shallow angle to the light, will often make it possible to see the diagonal 'photo. screen' lines. However, these diagonal screen lines are not always obvious because they can become a little blurred or clogged with phosphor ink.

'Photo' phosphor bands are printed continuously, so the bands extend across the entire top & bottom margins. The bands at the side margins are the same width as in all other positions across the sheet.
As a rule Wilding Coil issues have 'photo.' printed phosphor, whereas other sources have phosphor printed by one of the other methods or by 'photo.' All Green Phosphor issues are printed with 'photo.' phosphor and can be examined as standards for the features mentioned above..
'TYPO.' phosphor was applied by the typographic method, much like the familiar letterpress system, in which the (phosphor) ink is applied from the raised portions of the printing plate surface. The printing plate or roller is of metal, and so the edges of the bands are sharply defined.
The 'typo.' application of the phosphor normally leaves an impression of the roller on the stamp, presenting as 'tram-lines' down the stamp, visible on the reverse of the stamp coinciding with the edges of the phosphor band. The portion of the stamp between the phosphor displays a photonegative effect when viewed at a very shallow angle to the light (in the manner adopted when looking at phosphor bands by the naked eye in daylight, but setting the stamp at the shallowest angle possible).
Identifying Photo/Typo/Flexo Phosphor Printing on Queen Elizabeth II Wilding Definitives
'PHOTO.' Phosphor was applied by the photogravure printing process, for which the printing roller surface was 'photo-etched' with acid. The band printing area is composed of a multitude of diagonal screen lines (150 or 250 to the inch, set diagonally across the bands), and as they are photo-etched they are recessed into the cylinder surface, and are relatively shallow though deep enough to retain ink left from the inking roller; after inking excess ink is removed from the roller by the so-called 'doctor blade', leaving the ink in the screen lines, which is then applied to the stamps in the printing web.
As the 'photo.' screen is shallow there is no impression of 'tram-lines' left by the roller on the printed stamps. However, the portion of the plate which is not etched presses closely on the stamps and 'glazes' the portion of the stamp without phosphor, so this portion of the finished stamps appears slightly glossy when viewed at a very shallow angle to the light (in the manner adopted when looking at phosphor bands by the naked eye in daylight, but setting the stamp at the shallowest angle possible).
Careful examination of the 'photo.' phosphor band, by looking diagonally across the band at a very shallow angle to the light, will often make it possible to see the diagonal 'photo. screen' lines. However, these diagonal screen lines are not always obvious because they can become a little blurred or clogged with phosphor ink.

'Photo' phosphor bands are printed continuously, so the bands extend across the entire top & bottom margins. The bands at the side margins are the same width as in all other positions across the sheet.
As a rule Wilding Coil issues have 'photo.' printed phosphor, whereas other sources have phosphor printed by one of the other methods or by 'photo.' All Green Phosphor issues are printed with 'photo.' phosphor and can be examined as standards for the features mentioned above..
'TYPO.' phosphor was applied by the typographic method, much like the familiar letterpress system, in which the (phosphor) ink is applied from the raised portions of the printing plate surface. The printing plate or roller is of metal, and so the edges of the bands are sharply defined.

The 'typo.' application of the phosphor normally leaves an impression of the roller on the stamp, presenting as 'tram-lines' down the stamp, visible on the reverse of the stamp coinciding with the edges of the phosphor band. The portion of the stamp between the phosphor displays a photonegative effect when viewed at a very shallow angle to the light (in the manner adopted when looking at phosphor bands by the naked eye in daylight, but setting the stamp at the shallowest angle possible).

Typically, sheet issues of the 'typo.' printed two band phosphor stamps show a narrow '6mm.' band down the marginal side of side marginal stamps. These are listed by Stanley Gibbons as 'narrow band at left' or 'narrow band at right' varieties on the Typo. issues. All Phosphor Graphite two band issues have 'typo.' printed phosphor bands, exhibiting the 'tram-lines' on reverse in many cases, showing the 'narrow band at left or right' on side marginal copies, and also exhibiting the photonegative effect to the ink printing between the phosphor bands as mentioned above. So the Phosphor-Graphite issues can be taken as the standard to examine the features of 'typo.' phosphor.

'Typo.' phosphor bands stop short in the top and bottom margins of the sheet, though sometimes this is not obvious because the margins are guillotined close to the stamps cutting within the ends of the phosphor bands.
'Typo.' phosphor printing was used on both sheet and on some booklet panes of four issues. Doubt has been cast on the use of Typo. printing for phosphor on se-tenant 1d./3d. panes

'FLEXO.' phosphor bands are applied using rubber rollers inked with metal cylinders on which the 'phosphor bands' are photo-etched. As a result there is no impression of the printing plate on the stamps (that is there are no tram-lines to be seen on the reverse). Also there are normally no 'screen lines', or at best just traces of them, to be found as described under 'Photo' (above), because the photo etching for the phosphor in the 'Flexo.' process is applied to the inking cylinder and not to printing cylinder.
Differentiating between 'Photo.' and 'Flexo' printings cannot always be positive, so Stanley Gibbons do not list them separately, though they do mention which issues are printed with which phosphor printing process, so these notes are taken as the guide when I offer the different forms in 'Tony Bellew' listings. As a general rule 'Flexo.' Wilding issues are from booklets.

Controversy: there has been some debate over the incidence of Typo., Photo., or Flexo. printings of phosphor on some Wildings booklet issues in particular, resulting in an authoritative article and correspondence in the 'GB Journal' (published by the Great Britain Philatelic Society [see 'LINKS' page of this web-site for contact details to GBPS). In view of this the Tony Bellew stock listings do not include separate 'Typo.' or 'Flexo.' listings in the case of the 1d./3d. & 3d./1d. se-tenant panes for example, though singles or booklet panes, identified by the criteria outlined above, can be made available on request, subject to stock.


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 Post subject: Re: Phosphor afterglow on Wilding definitives
PostPosted: Tue Feb 16, 2016 9:41 pm 
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Mike,

Thank you for this extremely detailed, well-researched and presented article - it will, I am sure, be of great use to me, and hopefully other members.

Tony


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 Post subject: Re: Phosphor afterglow on Wilding definitives
PostPosted: Tue Feb 16, 2016 10:45 pm 
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Dear Tony - hands up - it was a copy of an article I read somewhere, copied because it may have come in useful at some point - which it has, probably breached copyright laws but glad it is of some help.
Mike


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