In reviewing various US tagged stamp candidates to post on the tagging DB I revisited the challenges around identifying 2179, 2179a & 2179b. Based on going through various single and plate blocks on information found here and elsewhere I believe there are 4, possibly 5 distinct varieties. I say 4 or 5 because it depends on how you want to split hairs around one of the varieties. Note I posted information along with tagged and untagged images at:http://www.stampsmarter.com/feature...ingView.html
Listed below are the key discriminators (color, gum, tagging & paper type under LW) I believe for each type/variety. I am going to work in reverse order from 2179b -2179 to start with simplest first:
Variety 4 (2179b) - key discriminators are tagging which is much grainier and gum which is shinier when compared to other varieties. For all other varieties, the tagging and gum looks essentially the same. Color alone should not be used as a discriminator as will hopefully become clear further below.
Variety 3 (2179a) – key discriminator for this one is ink color as the orange-brown color is fairly distinct compared against the others. Tagging is a smooth fine grain and paper is low-medium fluorescent with both of these two characteristic to close to the 2179 varieties to discriminate. Paper fluorescence appears somewhat less than 2179 but not enough based on samples I have seen to be a clear discriminator.
Variety 2 (2179) – key discriminator is paper type which is "Dead" under LW. I not seen to date any 2179a or 2179b on Dead paper. Tagging is a smooth fine grain and paper is medium fluorescent. Ink color appears much lighter when compared against 2179b almost like an under inked version of 2179b. P# 2 exhibits this variety based on what I have seen.
Variety 1 (2179) – Same as variety 2 except paper is medium fluorescent under LW. The difference in paper is quite distinct between Variety 2 and Variety 1. P# 2 also exhibits this variety.
Variety 0 (2179) – This is the wildcard potential 5th variety and can cause the most confusion if ink color along is used for discrimination. Tagging is a smooth fine grain and paper is medium fluorescent, same as Variety 1 – 2. Color of the ink is the challenge and where confusion can arise. Comparing the ink color of this version against 2179b they appear virtually the same to me. From my perspective, this variety seems to a heavier inking, which is why on the tagging DB I didn't break it out separately. The ink stands more proud from the surface of the stamp with a rounded looking surface. If you look closely at the ink of Varieties 1 or 2 you will see random areas where the ink appears thicker and rounded similar to this type. If splitting hairs and you want an additional variety you could call it a bright red-brown variety of 2179. P# 1 exhibits this variety again based on what I have seen.