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Ultra violet radiation of multiple crown Wilding definitives.

Cream and whiter papers.

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Fred Sellars28/01/2021 14:12:38
735 forum posts
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There are so many different features that have been created regarding security on many of the Machin stamps, it's sometimes hard to keep up with them all Julian.

The elliptical perfs began to appear in 1992 with the gold head high values £1-£5 which can involve two different shapes (rugby ball & sausage) dependent on which printer was used to print the stamps especially with the smaller format ones.

The patterned lettering in the background and the self adhesive plus many more variations, all of which can be found in the Connoisseur catalogue by James Skinner at .........

http://www.connoisseurcatalogue.net/catalogue.htm

But it's the different papers used to print the multiple crown Wildings of which is my concern Julian that appears to have been neglected in the past. Fred.

Fred Sellars24/03/2021 09:41:37
735 forum posts
360 photos

A previous attachment concerning a Machin stamp appeared to have been printed on a contaminated paper in a similar way to some of the Wilding stamps, which can only be observed with the use of a long wave ultraviolet light.

Here is a further trilogy concerning a specimen stamp that appears to have been printed on contaminated paper that I recently discovered, the stamps in question being 2 X 22p flame red PCP (AOP.) Giving three different views of the same stamps for comparison........

img_20210324_081558.jpg

img_20210323_224715.jpg

With the reversed view showing the contaminated paper ...........

img_20210323_230029.jpg

One can only compare like with like in order to assess the differences. Fred.

Fred Sellars14/05/2021 10:10:46
735 forum posts
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Fluorescence is a completely misunderstood and neglected aspect of philately, as with regards to the multiple crown Wilding stamp papers whereby only two types of paper have been listed in the specialised catalogue being that of cream and whiter.

The fact is that there are many more varieties of paper that have been used to print these stamps, in fact a chart has been created that gives a taper of between 0 to 12 for variations of fluorescence known as the Irwin scale provided by Mr Christopher McFetridge of Brixton Chrome >

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A mention of several variations of paper was also made by Mr Frank Walton RDP FRPSL.

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But unfortunately he did not have any higher fluorescent papers that could be observed as with some Wildings to be found that have previously been exhibited by myself on various occasions.

In my opinion the sooner that the higher fluorescent papers can be recognised and listed as being a variety the better. Fred.

Fred Sellars15/05/2021 09:33:14
735 forum posts
360 photos

With all the various shades of papers to be found, surely an adaptation of the Irwin scale could be adopted for the assessment of British stamp papers, as the cream and whiter definition alone appears to be inadequate and unsatisfactory based on some of the papers discovered. Fred.

Paul Davey 115/05/2021 10:10:13
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could you post a link to the Irwin scale definition?

cheers

Fred Sellars15/05/2021 11:07:22
735 forum posts
360 photos

Information regarding the Irwin scale has been obtained via Chris Mcfetridge in his blog over the study of a stamps paper.

Here is some further reading being the start of another blog.

img_20210515_104852.jpg

Fred.

Fred Sellars16/05/2021 09:09:06
735 forum posts
360 photos

The above in-depth blog can be found on the following link that relates to the published works of the Irwin scale on fluorescent papers Paul.

http://canadianphilately.blogspot.com/2017/08/the-papers-used-to-print-centennial_8.html

It makes interesting reading based on Canadian stamp papers. Fred.

Paul Davey 116/05/2021 11:48:56
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528 forum posts
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Thanks Fred - had seen these earlier. It still seems to be very subjective. I think what we need is a method to measure the fluorescence reproducibly and objectively. There is an ISO standard but I don't think it is directly applicable. Maybe a case for a philatelic modification?

Sounds like a topic for the Institute for Analytical Philately to investigate.- Maybe XRF would give some better measure?

https://www.analyticalphilately.org/

Perhaps a note published in the Analyst would prompt an offer of help?

It is a shame philatelists in the UK do not have access to a suite of techniques like the Smithsonian offer in the US.

Fred Sellars16/05/2021 12:42:34
735 forum posts
360 photos

Classifying the Irwin variation system as being subjective is nothing in comparison when looking at the classification of papers made by the RPSL & SG in only giving two alternatives, cream or whiter when defining the papers of the multiple crown Wilding stamps.

For example: the 3 stamps shown below are all classified as being printed on a whiter paper by both the RPSL & SG simply because they were printed long after 1962 and not because of their colour, it is obvious that they are not identical and need to be assessed accordingly.

img_20210516_005802.jpg

img_20210516_114630.jpg

I am sure that an indicator could be produced that when radiated would show all the variations from 0 to 12 and the stamp to be identified could be placed alongside such a device for comparison.

I know which system I would prefer and trust. Fred.

Fred Sellars21/08/2021 08:38:22
735 forum posts
360 photos

The strive towards whiter paper has led to more bleaching and a substantial increase of the concentration of fluorescent whitening agents (FWA) also known as optical brightening agents (OBA's) and violet-blue shading dyes added in paper.

FWA are dyes that absorb ultraviolet (UV) light and emit in the blue region of the spectrum, hence increasing the perceived whiteness by both increasing the lightness and the blueness of the paper.

Surface colour may change appearance depending on the illumination.

Colour is a visual sensation that depends on three interacting components: the light source, the object, and the observer.

Due to the complexity of the human visual system, several colour appearance phenomena that cannot be physically measured influence the way an observer perceives colour. One effect is simultaneous contrast that causes a stimulus to shift in colour appearance when the background or adjacent colours are changed.

This simultaneous contrast can affect the perceived whiteness of paper samples so that a pair of samples are ranked differently depending on the background and the shade of the other samples in the set to be evaluated.

In order to evaluate the perceived whiteness of a pair of paper samples with different tint, there is thus a need to model how the samples influence the appearance of each other based on comparison.

Many interesting articles on the above subject relating to whiteness and fluorescence in paper has been made by Ludovic Gustafsson Coppel, of the mid Sweden university in Diva portal reports.

HTML] Whiteness and Fluorescence in Paper: Perception and Optical Modelling

This thesis is about modelling and predicting the perceived whiteness of plain paper from the paper composition, including fluorescent whitening agents. Which includes psycho-physical modelling of perceived whiteness from measurable light reflectance properties.

Fred.

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