Another Tagging Question.

What is the difference between overall and solid tagging ? Example - 2257a / 2257c 10c canal boat transportation series.

STAMPOCD. I will try to answer your question. Overall tagging of 2257a is the same type of tagging as "block tagging". They are both applied to the web as if it were another color ( printed on the paper ).
Scott 2257c is printed on "Surface phosphor coated paper". It is my understanding that the paper here was coated by the papermill, before it ever got to the BEP.
I can not tell you how to distinguish between two stamps unless you have a plate numbered copy.
I have strips of all the different tagging and paper types of the Canal Boat, and my copy of plate 5 (2257c ) seems to be bright white, whereas 2257a has a blue tint.

Peter

Thanks P4522. As I was waiting for someone to reply to my question, I began reading the June issue of American Philatelist. Check out page 529. Does this have anything to do with what you are talking about ?

For overall tagging, taggant is applied over the printed design. For solid tagging, the taggant has already been applied to the paper (the paper is "pre-phosphored") before the design is printed. For this reason, the design on solid-tagged stamps generally appears clearer & sharper than that on overall-tagged stamps since said design is not being "clouded" by taggant. That being said, distinguishing overall from solid is not always as easy as this would seem to indicate.
The tagging on 2257a does appear bluish green whereas the other varieties appear yellowish green. I also agree with Peter that the tagging on 2257c (solid tagging) is brighter, a bright yellow green. If in doubt as to whether you've got 2257a or 2257c, look at both the tagging color under short UV and the gum. 2257c was produced only with low-gloss gum. 2257a can have shiny or dull gum.

STAMPOCD, I have not yet received my june American Philatelist. But I read the page on the APS website. Wayne Youngblood is trying to make a distinction between luminescence and phosphorescence. Yes that has something to do with it, but JLLebbert's explanation is better as far as your particular stamps are concerned. I tried to explain it a bit less technical.
One thing you may keep in mind, there is a lot of mis-information out there on tagging!

Peter