If like me you have no idea what’s going on here, it seems to be about book binding techniques/layouts. Just to save a few minutes of “what even is this?”
From what I gathered it's not about binding per se but the way to get from one sheet (the large paper you're printing on) to whatever format you're targeting, and that for the duodecimo (where you get 12 leaves / 24 pages out of a sheet) there is a "standard" imposition but the author found a "non-standard" one which they discovered by having a book with uncut "conjugates" (where two leaves are connected elsewhere than the spine, so you have to cut them apart to read the book) at unexpected positions.
In both you cut out and fold a strip of 4 and a strip of 8 (2x4) from your sheet in order to get 12 leaves. In the "standard", you then put the folded strip of 4 inside the strip of 8 (so when you enumerate the leaves from start to end you get the origins 8 8 8 8 4 4 4 4 8 8 8 8).
In the "non-standard" imposition — which the article says is mostly italian — you put the folded strips together in reverse (8 inside 4) so enumerating the leaves from start to end your origins are 4 4 8 8 8 8 8 8 8 8 4 4.
The article notes that you can also put both folded strips side by side (8 8 8 8 8 8 8 8 4 4 4 4 or the reverse) but then it's a bit awkward to bind as you get two groups instead of a single coherent one.
Weird. I took a course on Book History at U of T and I don't think we even covered 12mo.
Or I just plain forgot, or figured "why bother"... both of which are also as likely.
I used to run a couple small prints for my own amusement and don't think I ever ventured outside of quarto or ocatvo, but also probably because of the format of the paper I was using.
Re: the quirkiness of duodecimos, it seems like it'd be straightforward to fold it widthwise into thirds, then lengthwise into quarters, no? The first step there is pretty common for letterfolds, and the second step seems like it'd be common for sextodecimos.
