Paper

Paper is a thin mat of plant fibres, beaten in water, caught on a screen and dried until the fibres bond to one another. Lighter than bamboo slips and cheaper than silk or parchment, it carried writing and then print from Han China to the rest of the world.

What it is

Paper is a sheet of plant fibres that have been separated, mixed into water and left to settle into a thin mat. When the mat dries, the fibres hold together with no glue. Papyrus, by contrast, is made of strips of pith from the papyrus sedge pressed crosswise, and parchment is animal skin.

It can even be made from waste such as rags and worn fishing nets. For about two thousand years it has carried writing, print, money and maps.

The plate shows the European hand method, used until machines took over in the nineteenth century.

How it works

Paper owes its strength to cellulose, the long molecule of plant cell walls. Beaten in water, the fibres swell and split into fine fibrils. As the wet mat dries, the water pulls the fibres into close contact and hydrogen bonds form wherever they touch. Soaking undoes them, which is why wet paper tears so easily.

First the raw material becomes pulp. In China, bark, hemp and later bamboo were soaked, boiled and pounded. In Europe, linen and hemp rags were left to rot for some weeks, then beaten in troughs by wooden stampers lifted by cams on a waterwheel shaft.

Fine laid wires, heavier chain wires and a watermark sewn on in wire.

The pulp is stirred into a vat of water until it looks like thin milk. The vatman dips the mould, a wooden frame strung with fine wires, and brings it up level. A loose frame called the deckle sits on top and sets the edge of the sheet. As the water drains, he gives the mould a short shake both ways so the fibres settle in every direction and lock together.

The coucher turns the mould over onto a woollen felt, and the wet sheet stays on the felt. Felts and sheets pile up into a post, which goes into a screw press to squeeze out most of the water. The sheets then dry on lines. For pen and ink, European sheets were dipped in animal gelatine, without which ink spreads as on blotting paper.

How to make it

Bark, hemp, rags and old nets: the materials named in Cai Lun’s report of 105.

Cotton or linen rags, hemp and the inner bark of mulberry are the easiest fibres. Wood needs grinding machines or chemical cooking.

Prepare the fibre. Cut rags into small pieces. Soak them for several days, then beat them with a pestle or a mallet on a flat stone until a pinch shaken in a jar of water opens into a loose cloud with no threads left. Bark is first boiled for a few hours in water with wood ash, in an iron or stainless steel pot (never aluminium), then rinsed until the water runs clear and the fibre no longer feels slippery, and beaten.

Make the mould and deckle. Build two identical frames of straight-grained wood, the size of the sheet you want. Over one, stretch a fine screen: brass wire, closely woven cloth, or thin bamboo or grass stems tied side by side, as papermakers in Asia did. The bare frame is the deckle.

Form the sheet. Fill the tub with water and add pulp until it is cloudy. Hold mould and deckle together, slide them in at the far side, bring them up flat and shake gently as the water runs out.

Couch and press. Lift off the deckle, turn the mould face down onto a damp felt and press along the back so the sheet stays behind. Lay another felt on top and repeat. Press the stack between weighted boards or in a screw press.

Dry and size. Hang the sheets over a line, or brush them onto a smooth board. To write on them in ink, dip the dry sheets in warm, thin gelatine or starch paste and let them dry again.

Safety. Lye made from wood ash burns skin and eyes: wear gloves and eye protection, and boil fibre outdoors. The floor around a vat stays wet and slippery. Water-driven stampers and screw presses can crush fingers: before reaching in, disconnect the waterwheel, lock the stampers so they cannot fall and slacken the press.

History and evolution

For centuries the invention was credited to Cai Lun, an official at the Eastern Han court, who in 105 CE reported to the emperor a way of making paper from bark, hemp waste, rags and fishing nets. Archaeology has moved the date back: a fragment with a map drawn on it, from a tomb at Fangmatan in Gansu, dates from the second century BCE. Cai Lun most likely improved the process and made it practical for writing.

Papermaking reached Korea, Vietnam and, by the early seventh century, Japan. The story that Chinese prisoners taken at Talas in 751 brought it to Samarkand is doubted, since paper was used there earlier. From the Islamic world the craft reached Spain, where Xàtiva was making paper by the twelfth century.

On the paper machine the mould became an endless wire belt and the sheet became a continuous web.

In the thirteenth century the mills of Fabriano in Italy added water-driven stampers, gelatine sizing and watermarks. Ulman Stromer set up the first documented paper mill in German lands at Nuremberg in 1390.

In 1799 the Frenchman Louis-Nicolas Robert patented a machine that formed paper on an endless moving wire. The Fourdrinier brothers financed its development in England, and modern machines keep the same layout. In the 1840s Friedrich Gottlob Keller in Saxony and Charles Fenerty in Nova Scotia showed that ground wood could replace rags. Wood pulp made paper much cheaper and helped newspapers grow, but much of it was acidic, and many nineteenth-century books have turned yellow and brittle while fifteenth-century rag paper is still supple.