Ahem. ::cracks knuckles::
Glossary of terms.
In the process of making paper, one essentially takes dirty water called furnish( 99.5% water, 0.5% wood pulp) and drains almost all the water out in a controlled manner. A common way to accomplish this is to squirt the slurry (water and pulp) through a headbox onto a rapidly moving forming fabric, kinda like a screen, causing the individual fibers to align somewhat in the direction of motion, and the water to begin to drain out by gravity. This part of the process gives the paper “grain” and a top and a bottom side.
The second stage of de-watering involves pressing, or squeezing this wet muddy bunch of soggy wood fibers between hardened steel rollers. Often there is fabric, or felts on both sides of the very soggy conconction (maybe still 60% water) both to carry the stuff through the presses, and to absorb the water that is squeezed out. If there is only felt on ONE side (the bottom) then more water is absorbed out the bottom, and there may be a color difference between the two sides as well.
These felts carry the somewhat drier paper into the dryer section next, where the bulk of the rest of the water is removed by passing the paper over and under hot dryer cylinders at a lower pressure. It can pass through a size press next, which chemically seals up the surface for better printing. Many machines only size one side of the sheet, again leading to “print this side”.
Almost last is the calendar section, in which the paper is run between very hard rollers and pressed after it is almost dry. This gives the “finish” which can be smooth and glossy or grainy, depending on the surface of the rollers.
Finally, the paper comes out the end of this monstrous machine (maybe 10m wide and 200m long) and is wound up in reels for further slitting and cutting to be packed into those little 8 1/2" X 11", or A4 for you other folk, packets for your laser printer or photocopier.
The curl is a bad thing. Papermakers fight to remove it, but it is caused by the manner in which the paper dries, or by subsequent wetting and drying. Wood fibers swell axially when wet, then shrink back to a SMALLER size.
former Technical Service Engineer for a paper company that was swallowed up by International Paper.