|First Day Cover of Machins issued on 27 March 2013|
It has been known for many years that specially printed coil stamps are used for first day covers of self-adhesive Machins. I wrote about this in early 2010, and as Robert noted in a comment, this was first discovered and confirmed by the Modern British Philatelic Circle.
The first evidence for this was an identical phosphor shift on all four values on an FDC. This was a strong clue that all four stamps were printed together, side by side. As the MBPC editor said, "What can the chances be of stamps taken from random sheets exhibiting such identical displacements? Probably better than lining up the necessary half dozen numbers in the national lottery, but even so... It seems too much of a coincidence to occur naturally."
Further evidence provided by Douglas Myall is that the stamps are printed sideways right, a format that is typically used for horizontal coils, and that all the stamps have exactly the same displacement of the die-cut simulated perforations.
|Identical iridescent ink shift on the Machins|
Recently, I was looking at my FDC of the Machins issued on March 27, 2013. Similar to the identical phosphor band shift noted above, the five stamps on my FDC have the same shift of the iridescent ink used for the security overprint. As shown in the image above, the iridescent ink is shifted down and to the right.
If you have any FDCs of self-adhesive Machins, you might check them to see if they have phosphor or iridescent ink shifts.
Incidentally, Robert's advice is still valid - membership in the MBPC is a good idea for anyone who collects modern British stamps. Their journal is excellent, and their web site has much information and is continually being expanded and improved. Visit their web site at http://www.mbp-circle.co.uk or write to firstname.lastname@example.org.
PS: This is being posted in the waning hours of 2014 here in California, so I'll take this opportunity to wish all our readers happiness, good health, success, and a major philatelic find in 2015.