Great Britain Philatelic Society

I am creating a small exhibit on the early machin GB booklet panes for my local stamp club here in Phoenix, AZ and I was reviewing some material on GBstampbooklets.com and one area that interests me at the moment are the perforation varieties on stamp booklets. One comment in sheets and perforations article stated that sheets started with Perf I and then part way through 1968 changed to Perf P.

The question came to mind why? and for other types when? I seem to be getting into a deep dark hole here........

Is there some good reference material that has this type of information?

regards,
Martin

Martin, simple answer is that no one knows why they used a different sheet perforator resulting in change from perf I to perf P. But, the point is that the single value stamps were printed and perforated in the reel with the reel perforator imperf on outer edges and single perf every four rows between the no dot and dot sheets resulting in perf Ie. However, the panes to which you refer, two value panes, were single sheet printed and single sheet perforated - so different production processes. Harrison would have had a number of sheet perforators but if there was a technical reason for the change, I do not believe that it is recorded - but understandable that it can happen if a sheet perforator is used.
Regards, Ian Harvey

Thank you Ian