It was a Chinese official attached to the Imperial court, Ts’ai Lun, who discovered how to make paper in about AD 105. Until then most documents had been written on parchment, made from the skin of sheep or goats, or vellum, which is made from the skin of a calf. The ancient Egyptians had used papyrus, made from reeds beaten flat, but this was not a true paper, which is made from fibres that have been pulped, then reconstituted.
Though serviceable and very long lasting, parchment and vellum could never have coped with the growing demand for a material on which to store man’s unending accumulation of information. It has been estimated that a single book 200 pages long would have needed the skins of 12 sheep.
Ts’ai Lun made his paper from mulberry fibres, fish nets, old rags and waste hemp. Almost any fibrous material can be used for making paper. It is mashed to a pulp with water, bleached, sealed with a sizing agent to prevent too much ink absorption, then pressed into sheets.
Until 1850 the basic raw material was linen and cotton rags, which made excellent paper. But by then demand was growing so rapidly that a new raw material was needed. Wood pulp – usually from softwood trees such as conifers – was the answer.
Wood – indeed all pants – consists of cellulose, an organic material which forms strong fibres about 1/10 in (2.5mm) long. After felling, trees are turned into wood chips and fed into huge digesters where they are mixed with chemicals (usually sodium sulphate) and pressures to separate out the fibres and produce pulp.
Impurities, such as resin and pitch, are removed, the pulp is bleached, and mixed with chemicals to give it the right colour, or to make it whiter. The mixture then flows from a large tank with a narrow slit onto a moving screen which allows the water to drain away but retains most of the fibres. The sheet is pressed to remove more water and dried by passing around a series of steam-heated cylinders.
The paper may finally be coated with pigments such as clay, chalk, or titanium dioxide to improve its surface.
Picture Credit : Google
