The ancient papermaking process

Evolution. Cai Lun was therefore not the inventor of paper: what he did was probably to adopt, improve, and promote a previously available technology which had never been fully exploited. The process of improvement was then continued by his immediate successors, who experimented further with different basic ingredients, admixtures, and treatments to create a variety of improved papers. By the eighth century, when woodblock printing was invented within China and papermaking spread to the Arabs in Samarkand, paper was no longer an emerging technology: it was a highly refined product. Five centuries later still, the papermaking taught by Arabs to Spaniards and Italians in the thirteenth century was essentially the same art they have learned from the Chinese in the eighth.  Indeed, the paper on which Gutenberg printed his first bibles differed little from that on which the Chinese had first experimented with woodblock printing seven hundred years earlier. Even the first use of rag paper, long thought to be a Western invention, has now been confidently traced back to China.
 
Process. The basic stages of this classic process of papermaking were illustrated fifteen centuries after Cai Lun in woodcuts within the 17th-century history of technology by Song Yingxing (b. 1587).

• Step 1: Cutting, crushing, and moisturizing. First, plant fibres were cut, crushed, and ‘macerated’, that is, softened by being soaked in water.
• Step 2: Boiling. The macerated fibres were then cooked in an alkaline solution to break down the adhesives within them. After cooking, the fibres were typically taken outside to be repeatedly bleached by the sun and rinsed by the rain over a period of many months.
• Step 3: Casting the paper pulp. The bleached fibres were then pulverised and mixed with water and a gelatinous agent to help them bind together. The pulp suspended in the water was then scooped up onto a screen of fine bamboo slivers and expertly manipulated to form a thin layer of wet paper pulp.  
• Step 4: Pressing the paper. After draining, each sheet of paper was added to a pile, interspersed with felt sheets, which was then slowly compressed to squeeze out excess water.
• Step 5: Drying the sheets of paper. The individual damp sheets were then peeled off and brushed onto a flat, sometimes heated drying wall. Once dry, the sheets were trimmed and folded for storage.

Materials. Although bamboo is used in this series of illustrations, many different natural materials were used to make paper in China. In place of the cotton-roll fibres and reprocessed old rags later prominent in the West, China mainly used bast fibres (the strong inner bark fibres of plants and small trees such as hemp and mulberry, as well as lime and walnut) and grass fibres (such as rice straw, reeds and rushes), as well as rattan. Munro (The Paper Trail, p. 58) lists still other possibilities: cabbage stalks, thistles, St John's wort, turf, mallow, corn husks, genista, pine cones, potatoes, horse chestnut leaves, and jute, 'to name a few.'

Treatments. The paper could then be treated in a wide variety of ways: whether by the admixture of additional ingredients during production, or by surface treatment afterward.

Characteristics. The resulting paper can be very large (up to five metres long and nearly two metres high), very thin, lightweight, translucent, and not damaged by folding or rolling.

Credit: Howard Hotson (April 2019)