Paper
Papermaking was invented in China more than 1,800 years ago. By 1200 A.D., paper was being made in Spain, and in 1400’s the art was well established throughout Europe. The first paper mill in England was built in 1494. In the American colonies, paper was first commercially manufactured in 1690 in a mill in Philadelphia. Paper was originally made for uses other than printing but when the printing press was invented, it became one of the most important uses of paper.

Ancient papers were mostly made of rags and were produced with crude hand-operated devices. Most papers are currently produced from wood pulp. The machine for producing a continuous web of paper using a wire mesh screen to form the paper was invented in 1798 and is called a Fourdrinier. More recent advances are thermomechanical pulping, alkaline sizing, and use of recycled fibers.

First step in the papermaking process is the production of pulp using mostly wood. There are four types of pulping:
   •  Mechanical – mainly newsprint
   •  Chemical – removes impurities
   •  Semi-Chemical – combo of mechanical and chemical, imparts stiffness
   •  Thermomechanical – hot pressurized mechanical
Recycled pulp – popular in late 1980’s, made from old newspaper, office paper waste, magazines, catalogs…
Rag pulp – made from cotton – high quality strong paper

Bleaching – done on pulp to make a higher brightness in papers

Refining – pulp is passed between rotating and stationary set of steel bars which cause cutting and fibulation of the fibers. Produces desired strength and other qualities in paper

Additives – used for special properties in paper. Alkaline Papermaking--Calcium carbonate used as a filler and to improve brightness and opacity. Dyes and pigments for color and shade. Sizing, resistance to ink, and feathering.

Modern Paper Making Process –
Forming— pulp is diluted with process water. The water is drained through finely-woven wire by gravity and suction leaving the stock on the surface.
Press – the paper web leaves the wire still containing 75-85% water, so the presses remove more water by passing the sheet through rollers.
Drying – steam heated cast iron drums that the paper feeds through after the presses
Calendaring – stacks of vertical cast steel rolls, paper is compacted and smoothed progressively as it travels down the stack.
Supercalendaring – finishing process that imparts gloss and smoothness on the paper surface by passing through alternating steel and filled rolls

Handmade process –
Pulp – blend of a variety of materials
Slurry -  mixing pulp with water
Mold – wire mesh screen dipped into slurry
Deckle – frame around mold which produces a clean edge called a deckled edge
Couching – process of transferring the molded paper onto a flat surface
Drying – wait to air dry or run an iron over the paper

Coated Paper – dull to very glossy, have greater affinity for inks, greater smoothness, higher opacity and better ink holdout. Applied by rolls, air knives, or trailing blades.

Paper finishing – complex paper property related to its smoothness

Top (Felt) Side and Wire Side – paper is a two sided material. The side directly in contact with the wire is the wire side; the other side is the felt side.
Felt side usually has less grain and more filler. The wire side has more fiber.

Grain – refers to the position of the fibers. Most fibers are oriented with their length parallel to the paper machine (machine direction) and the width running across the machine (cross direction).
1. Paper folds smoothly with the grain direction and roughens or cracks when folding cross grain.
2. Paper is stiffer in the grain direction.
3. Paper expands or contracts more in the cross direction.
4. In books, the grain direction should be parallel with the binding edge. 

Weight – Paper is commonly identified by the weight of a ream (500 sheets):
20-pound bond, 70-pound coated, etc…. 

Strength – paper is more dependent on the nature of its fiber than its thickness. Closely intermingling long pulp fibers produce high strength.

Paper Qualities – can affect the appearance of the printed image on paper: color, brightness, opacity, smoothness, gloss, refractiveness

Paper Grade – paper is defined in terms of its use. Each grade serves a purpose, usually suggested by its grade name: bond, coated, text, cover, book, offset, index, label, tag, newsprint, lightweight, digital.

(images from A Guide to Graphic Print Production. Johansson, Lundberg, Ryberg. John Wiley & Sons, Inc. Hoboken, New Jersey. 2007.)