Another eMail from Brian Horton
Many thanks for describing the notched bands in such detail, it seems there is more to learn about these issues than one thought, with all the hidden secrets of specialisation perhaps Machins are a lifetime study in their own right.
Another question if you would be so good as to ( if possible) answer. I have seen the expression Jet Phosphor used in conjunction with certain Machins, even after a Google search I can not find any information on this topic. Anything at all concerning this topic that you can tell me would be appreciated.
Hello Brian and all visitors ( readers)
This is a subject known to specialists who are the main collectors of Jet phosphors. John E. Thompson discovered this variety of phosphor used to print phosphor bands on Machins. This phosphor was named JET by philatelists after Thompsons initials. The Post Office actually knew of the error and named it Yellow Phosphor.
Although these were printed in 1973 and were mentioned in some early catalogues they did not gain a permanent catalogue status in the Connoisseur until August 1995.
The anomaly resulted from an error at the printers Harrison & Sons sometime in the early months of 1973, when a zinc sulphide solution was inadvertently mixed with the normal purple phosphor ink.
It was estimated and has now been established from records of printing dates that certain printings in the second and third week of May 1973 were affected.
This error is most easily identified by testing the stamps for a reaction to long wave ultraviolet light. Usually stamps from this period (normal stamps) react only to shortwave UV, but those with JET phosphor react to long wave as well.
Jet Phosphor was found on several low value Machins printed during the period mentioned above. Twelve national definitives and four regional stamps have been affected (discovered).
I hope this helps.
Do you have a question? I can not promise that I know the answer, if I do not I may be able to find someone who does.