UK Machin 25p Rose Red - Help Identifying Different Versions

First apologies for the poor quality photos.

The first photo shows 2 25p stamps



The next shows the same stamps under UV short wave light. One stamp appears much darker than the other - any reason for this?



The next photo shows 2 different stamps under UV light. This stamp has variants with yellow and blue phosphor bands. The stamp on the left has blue phosphor band but the one on the right appears to have normal uncoloured phosphor bands. Any suggested reason for this?

The one of the left is a 2 band. If is litho printed it is SG Y1775. If it gravure it is Y1690. The right one looks like a 2 band too but not sure if I see a reflection. It may be different in tagging = blue vs yellow.

The value outline is irregular (jagged) under a magnifying glass on gravure stamps.

Y1689 25p rose-red OFPP Grav E P15x14 sheets
Y1689 25p rose-red OFPP Grav E P15x14 c-v
Y1689 25p rose-red OFPP Grav E P15x14 booklet
Y1690 25p rose-red 2B-Y Grav E P15x14 sheets
Y1690 25p rose-red 2B-Y Grav E P15x14 c-v
Y1690 25p rose-red 2B-Y Grav E P15x14 booklet
Y1690 25p rose-red 2B-B Grav E P15x14 c-v
Y1690 25p rose-red 2B-B Grav E P15x14 sheets
Y1690 25p rose-red 2B-B Grav E P15x14 booklet
Y1775 25p red 2B-Y Litho E P15x14 booklet
Y1775 25p red 2B-B Litho E P15x14 booklet

Thanks angore - in the bottom picture both stamps have two bands - I have versions with both blue and yellow bands which are quite clear to distinguish. The stamp on the right has two bands which appear to have no colour which is what I am trying to work out what it is or whether the colour has been somehow been washed off.

The phosphor on Machins appears sensitive to soaking, etc. Unused ones are usually more consistent. Yellow is usually the easiest to see.

There are two different types of blue phosphor too. Deegam assigns the codes AB and A2B. The difference between the two is in how they react to both long wave and short wave UV light, and the duration of the afterglow.

Not sure if the two types apply to your 25p Machins though.

Robert

Adminware's pages refer to a 2B-Blue and 2B-Violet but have not tried to study the difference yet.

Here are my notes on the differences.

Robert

That correlates to the names used by Adminware. I would not expect any phosphorescence under long wave UV. Is there a Machin tagging that demonstrates phosphorescence under long wave?

All GB phosphors demonstrate long wave afterglow, but only under optimum conditions, and at the right wavelength to activate it.

My observations under long wave UV probably failed to meet both criteria.

Robert

This 25p stamp with blue fluorescence only exists with Deegam's AB phosphor. Harrison and Enschedé used different paper providers. It may also account for differences in the fluorescence of the paper. The Enschedé stamps have 9.5 mm phosphor bars and the Harrison ones have 9 mm bars. Lithography stamps were printed by Questa and Walsall. Walsall printed 8 mm bars, Questa both 8mm and 9 mm bars. The original stamps by Harrison did not have phosphor bars. The 8 mm bars are yellow fluorescence stamps. Questa's ellipses - they come in two shapes - differ from those of Walsall.

Use a stamp that has only one bar width to determine the width of bars from the gap between the bars.

Angore wrote how to discern lithography and photogravure/gravure stamps.

If you have a good magnifier, look at the perforation tips. If these are jagged, you have sheet stamps or stamps from Prestige books (Questa lithography only, but Questa did not print this value in sheets). If there are sides that have straight cut perforation tips, you have a booklet or coil stamp. Coil stamps have two opposite sides cut straight. Booklet stamps have one or two sides cut straight. For booklets, the two sides will be adjoining sides.

Head types can also help identify stamps as can direction of printing. But that is in the realms of very specialised collecting (Deegam was mentioned).

In general, a specialist dealer like John M. Deering will also discern dull, very dull and bright fluorescence for the blue fluorescence stamps. But that tends to be a relative description and applies to later stamps.