As a matter of course I check all my stamps under both long wave and short wave lamps as well as natural light.
I have a number of the above stamps all identical ( more or less ) in both natural and under long wave light.
However under short wave light while most react with varying intensity of white, one produces a bright yellow reaction. Also on this stamp ( and a couple of others ) the engraving reacts with a strong purple hue, and appears much sharper than normal.
Are these recognised variations to the normal, and has anyone any bright ( groan -pun warning) ideas as to the reasons. I thought the yellow might be some sort of contamination from the soaking process- I only collect used stamps, but I am at a loss about the other phenomenon.
I guess being a low-value "make-up value" stamp it was probably in circulation for a long time with multiple reprints. These are not often thoroughly studied as being too "modern" to be philatelically interesting.
