Paper Expansion & Shrinkage Affects Perfins and Perforations
By John Jamieson — October 2000
On the issue of minor perforation variations that are considered so important in trying to isolate printings...
I have a little story that puts the "paper expansion" issue into proper context. A couple of months ago Don, here in my office, was pricing up some OHMS Perfins. He was carefully checking each stamp against the standard 5-hole OHMS template (which was based on a block of 15 formerly in John Johnson's collection and is now in the Canadian Postal Archives). This is the standard reference on these issues, similar to the Kiusalas gauge for perforations.
He had one of the more valuable items which matched perfectly to the template but had a big hinge which he thought should be soaked off. So, the stamp went into the water and was soaked for about 20 minutes which nicely removed the hinge. Don then put the stamp between plastic card and blotter and into his small Thor stamp press and tightened it up very snuggly (Don has rather large muscular shoulders). In due course he removed the stamp from the press and IT NO LONGER MATCHED THE TEMPLATE. The pressure of the stamp press had "squished" the wet stamp enough to expand it by enough to affect the alignment of the adjacent OHMS perfins. The change was perhaps 0.2mm, a tiny amount indeed but enough to throw out the measurement.
He brought the stamp to me as it was now a problem as it did not align (and anyone carefully examining it against the template was going to immediately question its authenticity). I suggested that he put the stamp back in the water for an hour and then just pat it dry and let it finish drying in the air. The result was the stamp returned to its previous size and the OHMS perfin again matched the template perfectly.
The obvious moral of this story is that soaking stamps really does affect the paper size and must be considered. In this case the change was only 0.2mm over a space of approximately 26.0mm (26.0 vs. 25.8 before the pressure was applied + 0.78%). Not much, however, when you are comparing 12.0 to 12.1 it matters. It is enough to change 12.0 x1.0078 to 12.09 which would certainly make any observer record it as 12.1. Following from this 11.5 x 1.0078 = 11.59, 11.7 x 1.0078 = 11.79. Since 26.0mm is about the length of the edges on most Large Queens and the sides on the Small Queens this is significant.
I would recommend anyone seriously studying the minor perf differences do some experiments on this matter to prove to themselves how significant this issue is. Take a dozen of your common stamps (some vertical and some horizontally wove) and measure the perfs (and the dimensions if you care) carefully. Then soak them for 1/2 hour in luke-warm water. Then put them between a plastic card and a blotter in a stamp press and leave them for at least a couple of hours until completely dry. There must be significant pressure applied. I would doubt that a single big dictionary would do the job. Anyone who does not have one of the little Thor stamp presses I referred to above and does any woodworking could fabricate a suitable press using a couple of pieces of board and a couple of c-clamps. Make it tight.
THEN, remove the stamps from the press and measure the perforations (& dimensions if you wish) again.
Keep in mind that the expansion will be greater against the weave. If stamp is on vertical wove paper the stamp will expand more in the horizontal direction and this will "reduce" the perforation measurement across the top of the stamp. You will notice a larger difference on the longer side of the stamp so, on a LQ or SQ a stamp with horizontal wove will be a better sample to use as the expansion will be a bit more significant along the longer vertical sides. My bet is you get a 0.05 to 0.10 difference in the perforations.
After you measure your findings you can then "re-soak" the stamps and this time just lightly pat them dry with a paper towel and let them dry in the air with no pressure. Then check them again and see what the perforations measure. My bet is you will find they are all pretty much back to where they were when you started.
The other thing that will affect the perforation measurements is whether the examples used have even the slightest amount of gum residue on the back before you start. This can be with original stamp glue or the gum from previous hinges. This gum will likely have shrunk the stamp a tiny bit and might make a very slight difference if you are really accurate with your measuring.