angore
Member 
Posts: 5,348 
What I collect: WW, focus on British Empire
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Post by angore on Dec 16, 2019 23:09:24 GMT
I spent some time capturing SW UV images of the Machin ACP/PCP phoshorised paper types. The stamps on left are PCP and the ones on the right are ACP. These were only available in one paper type. ACP is described as as very white in appearance and strong afterglow under SW. PCP is described as having a dull appearance and weak afterglow under SW. The 24p exhibits the right characteristics (bright, strong after glow) for PCP and 23p would fit the PCP definition. The other two do not. The 23p on right exhibits no real afterglow but is a wee bit brighter. The 13½p is bright but then it is the unused one of the bunch. Oh well. I wonder how the experts figure it out in some objective form. I was hoping to have a standard and wonder if some can never be identified due to some condition (used, etc).  |
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Ryan
Member
Calgary, Alberta, Canada
Posts: 2,721
What I collect: If I have a catalogue for it, I collect it. And I have many catalogues ....
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Post by Ryan on Dec 17, 2019 0:43:41 GMT
I don't know enough about these coated papers to help you, but I know that the single or double bars used as tagging are prone to losing much of their strength when soaking used stamps off of envelopes. The strength of tagging can gradually weaken the longer the stamp is soaked, so you can find an entire range of phosphorescence strengths on soaked stamps, ranging from almost-like-a-mint-stamp to almost-impossible-to-see-anything. So, I don't know if you'll necessarily be able to make judgments about paper coating types on these used, soaked stamps. Certainly for the bar tagged stamps they're problematic, maybe they are for the overall tagged stamps too.
Ryan
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Post by feebletodix on Dec 17, 2019 9:48:07 GMT
To quote Stoneham
"Collectors tend to serperate the phosphor coated stamps with the matt finish PCP1 from those with a glossy finish PCP2. Unfortunately while good examples of either are clearly distinguished, a grey are exists where classification is difficult. This difference is caused by the heat on the paper during the drying process. The PO did not like the variance in quality and therefore requested an improvement. The result is ACP which is produced differently to PCP. Not only is it brighter than PCP it is also consistent in printing quality."
I think 'used' fall into the grey area and you would need a lot to find good clear examples
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angore
Member
Posts: 5,348
What I collect: WW, focus on British Empire
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Post by angore on Dec 17, 2019 16:30:52 GMT
Thanks. I know from experience used Machin poses challenge for tagging in general. I will likely abandoned phospored paper variety (ACP/PCP) differences.
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angore
Member
Posts: 5,348
What I collect: WW, focus on British Empire
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Post by angore on Dec 20, 2019 18:55:25 GMT
Here are a couple more images. The first is with mint stamps. Left is X952 PCP paper, right is X936 ACP. The difference is clearer and the ACP did have a slight afterglow. This image is side illuminated with lamp on each side.  This stamp was printed in PPP, ACP, and PCP. The left image was clearly brighter. I believe the right is PPP and appears like a stain. I have another 1p crimson that looks similar and it was also available in PPP.
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Post by dgdecker on Dec 21, 2019 3:16:44 GMT
This is why I have limited myself in the area of interest. Too many varieties to work with. I am glad that are others out there that do have this interest. My goal is to simple have. One mint copy of each issue . Like any collector, that can change at any time.
david
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angore
Member
Posts: 5,348
What I collect: WW, focus on British Empire
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Post by angore on Dec 21, 2019 12:24:52 GMT
Except for the PCP/ACP, etc, this has been the only area that is variable for what I want to collect that is variable (can be hard to be 100%). The challenge is once you pick a variety to collect it can morph into a lot more issues you can collect due to combinations possible.
For rest of my collection, I usually limit it to Scott minor varieties. Steiner pages usually provide spaces for most minor varieties and can create my own extra pages if needed.
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