Canada 1/2c Small Queen, 2 Stamps, 2 Different Sizes, Need Help

Ok, from what I am reading aout the small queens is that there were different printings of these, and many places mention the paper types, perforations, re-entries etc.., but I have, so far, not seen anything mentioning the actual size of the stamp design being different.

I have these 2 examples, one unused, one used. When overlaid on top of ech other, the used stamp is noticeably shorter, top to bottom. The side to side measurements are the same however. What accounts for one stamp, seemingly, being either "stretched" or shrunk in one direction only? Different printing methods, maybe rotary vs. flat plate?

Establish the direction of paper - grain, mesh!

First thing to do when you suspect variation in size of recess printed stamps....

In 19th century Canada, stamps were printed on dampened paper to facilitate the transfer of ink from the recessed plates. As the paper dried (prior to gumming and perforating) it shrunk thereby creating varying image sizes.
GJP

I'll have a closer look at the paper when I get home tonight. Thanks!

should not have been used always the same paper grain for the same stamp?
or asked in a different way: is this really common that the stamps of early Canada have such different sizes?

I don't know this from the US classic stamps, as there the size difference has always an importance (and which is why spain1850 asked this perhaps).

From what I have seen this series was printed over many years and different papers were indeed used.

yes, maybe it's different from the US classic stamps as the Canadian stamps didn't have watermarks and they didn't have to care about the paper direction? On the other hand, from the bank note era (1870-80s) of US stamps I have never heard of any size differences, so still I think this is an interesting find.

One stamp is unused and the other is used. Have you compared the unused stamp with another unused stamp? Have you compared the used stamp with another used stamp?

Just establish the direction of paper BEFORE damaging a mint stamp ....

Apples and pears are in the same family of fruit trees!

There is a thicker white paper variant known on the issue. It is more dimensionally stable to wetting and drying. Most were printed on poorer quality thin paper of coarse structure and off-white in tone.