Welcome to this first Theory Thursday! If you missed the introduction to this ‘paper’ series, it can be found: here, as a guest post on Rachel’s blog. Today I’m going to babble about grain direction in paper. This is one of the favorite topics of every bookbinder I know. If you don’t want to know about paper grain direction, head directly to the end of this post: The video about Korean papermaking is embedded at the bottom and is well worth a view in any case.
Experiencing and Determining Paper Grain Direction
Take a rectangular piece or sheet of office paper and wet it from only one side. For example with a brush, or by placing it on top of water. In one direction it will be staying straight and in the other direction it curls up thus almost forming a tube. If you take other sheets from the same pack or other pieces from the same sheet you will note that it is always the same direction that stays flat (the grain direction) and the other direction that curls up (cross grain direction).
This is because the paper stretches more in one direction than in the other when it gets wet.
Another way of testing paper grain direction
Take a sheet of paper. Bend it double without really folding it and gently lay your hand on the curved fold. If folded across the grain direction it will resist your hand more and feel more springy than when folded with the paper grain.
Consequences for Bookbinding
Both properties make it necessary to bind the pages in a book such that the grain direction runs parallel with the spine: The signatures fold better and nicer (otherwise one often gets unaesthetic ripples along the crease) and the whole book reacts better to the moisture to that it will be exposed inevitably, even if you are binding a book without glue. For example there is always some moisture in the air. The degree of moisture will vary though time, and thus the book block ‘works’ and moves a bit all the time. Books bound across the grain will curl up unpleasantly or maybe, in the worst case, can’t be opened properly anymore.
But what exactly is paper grain and how does it get a direction
Paper is sieved and dried from a watery suspension (slurry). The details of how exactly the slurry is composed can vary immensely depending on what the desired properties of the paper are. But the common thing about all papermaking, no matter whether you end up with really thin Japanese paper, thick rag paper or standard office paper, is that you start from a slurry that contains fibers that will form the base structure of the finished paper. The slurry is spread onto sieves, dried and then further treated.
How the paper is put onto the sieve and how it is dried effects the paper grain direction. Industrially produced paper comes in long rolls, more or less in an endless strip which moves at quite a speed through the machines. This movement makes the fibers orient themselves mainly in the direction in which the conveyor belt (or rather conveyor sieve) moves, just like you would expect from strings floating in flowing water.
When paper is made by hand, individual sheets are pulled with a sieve from a vat. In that process, the fibers arrange themselves randomly, and therefore without a specific direction. (Like you would expect from strings floating in still water.) So handmade paper expands evenly when wet, without curling up. But this does not necessarily make it preferable to bookbinders. Many other materials, for example the book cloth also have a fiber direction. Wen glued together all the strain and pull that is induced by the materials have to be balanced so that in the end you end up with something flat.
I picked some videos about industrial and hand papermaking. If you want to see more, check this playlist that I also put together for you.
The first video shows industrial papermaking:
This video shows a special Korean way of making paper by hand:
That’s it for today.
I hope you enjoyed this post about paper and papermaking. Next week I’ll still be talking about paper. (Probably I’ll have more information about traditional papermaking in Europe and rag paper. – But the post is not finished yet. So, no promises.)