Today, books are everywhere, in one form or another.  But in the Regency era, most people could not afford books.  The nobility could, but even they rarely had what we would call a  large collection today. To have a few hundred books was
remarkable, and worth quite a fortune.

Books were laboriously printed, where every single letter was a tiny piece of
lead type, that had to be hand laid into a frame, to print the pages.   One
consequence of this was that books were often first published in a serialized
fashion, so that they could be released faster.  The paper that they used was
also thicker than today’s paper, as the processes for making it had not yet
evolved to achieve the effortless quality of thin paper that is made now.  So – a
longer book was much fatter.

To make the process of printing easier for the printers, rather than print one page at a time, multiple pages were printed on one huge sheet, (which was printed both sides, to a very cleverly planned pattern, so that all of the pages ended up in the right order after folding) and the result was folded in a specific way down to the individual page size.  Each bundle of pages was stitched down the fold that aligned with the spine of the book. (which is where the process that some note books are still made by today came from).  This meant that, when the book was assembled (each bundle stacked on the others in the right order, and the whole stitched together across the width of the spine), either a top of bottom edge, or the opening long side of the book had many instances where the pages were still joined together, by a fold (which side these ‘unopened/ uncut pages were depended on the fold pattern used).

To be able to read the book, you needed to take a sharp flat paper knife, and slice along the fold to separate the pages (see picture above to understand what this looks like. The book in the picture has closed folds at both the right hand side of pages and the top of pages.So, when you see a very old book, with rough and a little uneven edges, it is likely because whoever cut the pages did so not so evenly or smoothly.  Books were also often first sold to a buyer with their pages rough edged, most uncut, and in a temporary light cloth binding.  The buyer then took the book to a binding specialist, to get a good quality leather binding in the color and texture of their choice made, and the pages bound into it.

So… next time you read a paper book, imagine being there in the Regency Era, and having to keep slicing the pages apart, the first time that you read a book, just so that you could turn the page!