Still A Little Confused On Printing Processes - Flat Plate Vs Offset

I can't relate to your possible "barking up the wrong tree," because I have a few questions in my way. If my "tree" is right, then you are at the wrong one.

How many panes does the (as sold) vending booklet have? The total value I get from the 1 pane front pictured seems quite low for a vended product. If there were "two" panes or more, then I'd expect to see set off on backs of all but the last pane. You see your answer then. (I'm surprised you short-changed your question by not showing the full pane's backside. That 1c stamp is also recess engraved and there should be, even if tiny dots, some set off ink on it as well when there's set off for the 5c.)

At my "tree", we're not focusing on length of ink drying of recess-engraved lay-down vs. gravure lay-down. We focus on the fact that being recess-engraved, the ink is literally raised slightly above the paper (think security engraving on $ currency bills).

So obviously over time the normal pressure on the booklets can have some of that ink set off on "glue". Yes, the other factor is the glue; a given amount of time and pressure might NOT have set off (yet) on other surfaces (e.g., no-gum or plain paper). This also suggests looking closely at the back of the FRONT COVER of said booklet, for it might or might not show set off as well... but it has no "glue" (i.e., gummy substance that's amenable to grabbing such ink, given enough pressure and/or time.) (And we now know what it means if you now find such set off...)

@bk80,

I do not know whether it is possible.

Looking at the pictures you posted raises the question whether this could be suffusion rather than an offset.

I am wondering whether the apparent suggestion by StampsOnMail that gum on the back of a stamp would easier pick up ink from another stamp than a booklet cover holds true.

I am not familiar with Canadian stamps. British and Dutch booklet covers, certainly from that period, tend to be porous. I would expect porous material to pick up ink much easier than gum.

Is the setoff under or over the gum?

Under. Ink on top of gum usually means that some stamps got stuck together at some point.

Unless the reel of paper was gummed before printing.

Not U.S. stamps of this era. Printed, then gummed, then perforated.

The OP was about US stamps, but a follow-up question was about Canadian stamps. I, of course, am assuming stamps showing the portrait of H.M. Queen Elizabeth II with the inscription "CANADA" are Canadian.

Wow! Great questions and I will do my best to answer them as best I can. The Canadian 1979 vending booklet contained one pane. Value 50c. The pane never touches another pane in the booklet as there is only one pane. (The panes are printed in four columns of about 14,000 consecutive rows, then perforated but not slit apart. They are all attached together and are rewound on a spindle waiting for the next step which is to slit one column completely off and glue those panes still attached together on to cardstock. Then and only then are the booklets cut apart when still flat and then folded). It must be interesting to watch.



Here are three panes to show how the setoff is quite random horizontally but always in the same vertical position. These panes were printed on pre-gummed paper.