Between the sheets

Where has that smooth sheet of pristine new paper been before it reaches you? Fay Sweet tells the story

Though paper remains the designer’s most-used medium, its complexities and fascinations remain something of a mystery. Here, then, is the story of how paper gets from the forest to the drawing board.

The amazing trick pulled off by the paper industry is how to turn thumping great big trees into sheets of gorgeous, diaphanous papers.

The secret was discovered in China in 105AD by a court official, T’sai Lun. The expert calli graphers were frustrated by having to work with cumbersome materials like woven cloth. So T’sai Lun was inspired to produce something smoother. His felt-like invention was made of macerated vegetable fibres (some stories have it as old fishing nets) which, when spread evenly and dried on a bamboo screen, made a flat and absorbent writing surface.

Those basic principles have changed little in today’s paper-making mills, though trees have taken the place of old nets. Trees are the ideal basic ingredient as wood is composed of millions of tough fibres stuck together with a naturally sticky binding, cellulose. Once the tree is mashed up or macerated to form pulp, the jelly still clings to the wood fibres and helps them reform when transformed into sheet paper.

Contrary to popular belief, the modern forestry industry is extremely environmentally aware and incredibly efficient at making the most of just about every bit of a tree. Most full-grown trees are put to a number of uses – for example, after the bark has been stripped, the central part of the trunk becomes construction timber, smaller pieces are used for particleboard and chipboard and the rest makes paper.

After the wood has left the forest it is turned into pulp – this can be achieved mechanically, in massive grinding machines; or chemically, where a substance is used to cook the wood in huge vats and break it down into a mulch. The mechanical process is quick and produces a high yield per tonne of wood. Because it is so aggressive, it chops the fibres and makes a rough-and-ready pulp – this is the stuff of cardboard, newsprint and cheap paperback books.

Mechanical pulp-making is a high energy user, while chemical processing is largely energy self-sufficient. The chemical process produces a lower yield of higher quality pulp made of longer and stronger fibres, and is usually bleached to prevent yellowing. The bleaching was once achieved by using chlorine gas, but, in response to environmental concerns, many mills now make more use of the preferred oxygen, chlorine dioxide and hydrogen peroxide. The cooking process has also undergone modification to reduce the use of harsh chemicals. Both methods produce virgin fibres. Pulp can then be given various additives to produce different final results; for example, sizing increases the water repellent features of the paper. Without sizing, paper is a blotting pad.

The smooth, creamy white pulp mixture is fed evenly on to a conveyor belt, and the different textures of the belt produce different, very subtle textures in the paper. This belt is a wire or plastic sieve-like mesh which allows much of the moisture to run off, leaving a pulp slurry. The movement of the belt makes the fibres line up and this gives paper its “grain” – tear a newspaper from top to bottom or side to side and it’s easy to tell which way the grain lies. At this stage a dandy roll can be used to impress a watermark on the paper. The roll “kisses” the paper surface to disturb the fibres – watermarks are composed of thin and thick areas of paper.

The thin film of pulp is pressed on absorbent blankets and between steel rollers, and dried to make paper sheets. Surface sizing can be added to improve strength and further prevent moisture absorption. And there’s calendering, where the sheet is passed between steel rollers – the more pressure that’s applied, the thinner the sheet. Coating is another part of the finishing process – mixtures largely composed of fine china clays are applied to the surface which again improve print performance. Then there are the options of glazing, for a shiny surface, laminating, for a thin plastic surface, embossing, for a textured surface, and so on.

From here the paper is spooled on to rolls or cut into sheets and then makes its way to the merchant… but that’s another story.

The Really Useful Paper Glossary

Laid and wove: These terms describe part of the finish of a paper, particularly stationery paper. The differences can best be seen by holding a sheet up to the light – a laid sheet will show a ribbed pattern, achieved when the paper is made on an open-weave wire or plastic mesh. Wove paper is made on a base of closely-woven wire cloth and so gives a more even appearance. Both effects are subtle.

Cotton or rag: Paper made using a high proportion of cotton and linen rag. The fibres are chopped and crushed and blended into a watery, sticky porridge-like mix which is eventually transformed into sheets of paper. Some paper is now called cotton-rich, which means a percentage of the mix is cotton with the rest made of wood pulp. The paper still retains a lovely soft texture.

Coated and uncoated: Many papers are available in either a coated or uncoated finish – the coating is usually a fine china clay and latex mix which is applied very thinly to the paper surface to fill all the dips and tiny holes. It gives an extremely smooth surface to the final sheet which allows it to take ink extremely well. Printing results will be crisp and sharp. Depending on the end use, there is the option of gloss or matt coated. Uncoated papers have a slightly less refined, more rustic feel. Printing is a little softer and less brash in appearance.

Board: You may be forgiven for thinking this is a simple classification, but no. No one really knows what constitutes “board”. The line where thick paper ends and board begins remains unclear.

Weights and measures: Gsm, gm2 and microns are all ways of specifying weights and thicknesses of paper and board. Gsm and gm2 both mean grams per square metre and that is a weight – hence 100 gsm will be considerably thinner than 300 gsm. However, depending on how the paper is made, some are more tightly packed than others – there can be considerable differences in texture and look in two 100 gsm sheets produced by different manufacturers. If you’re not sure, ask for samples – there’s no better way of testing a paper’s appeal than by having it in your hand. Microns are a measurement of thickness; this is often used for boards instead of the gsm measurement.

Virgin fibre: Paper made entirely from pulp during its first incarnation, ie straight from the tree. Once paper is recycled in any way, it is no longer a virgin fibre. Virgin pulp is prized because it tends to be stronger, more flexible and more durable than recycled material.

Mechanical wood pulp: Pulp made by chewing up a tree using mechanical energy. The process is harsh on the wood fibres and the pulp is considered inferior to chemical pulp.

It produces a high yield of paper per tonne of wood.

Chemical wood pulp: Pulp made using chemicals to break down the wood. The chemical dissolves the wood’s bonding agents and produces high quality pulp composed of long, strong, flexible fibres.

Woodfree: This is one of the oddest terms in paper-making. It means a pulp or paper which contains no mechanical wood pulp (see above). It does not mean the paper is made from a material other than wood.

ECF and TCF: Elemental chlorine free and totally chlorine free. Chlorine use in bleaching paper has acquired a bad name from the green lobby, and paper makers have reduced the amount of the chemical used. For the totally green buyer, TCF is more highly prized than ECF.

Recycled, recyclable: A couple of words that have caused a lot of confusion. Recyclable is easy: this is paper that can be put back in the pot, mulched down into pulp and used again to make recycled paper. Recycled can mean a paper containing 100 per cent recycled material or just a proportion – most manufacturers now state this on the pack. The type of recycled material is also important: pre-consumer waste means end of reels and printers offcuts, usually material that’s not been printed. Post-consumer waste means paper that has been printed on and been used by the consumer. The green lobby favours the use of post-consumer waste because the option for disposing of this stuff is burial in a landfill pit.

There is a huge debate about the value and importance of recycled paper. Some say the de-inking process is so energy-consuming that recycling is a waste of time. Others point out that trees are a crop intended for paper making and so recycling is a waste of time. Others claim that once we improve recycling methods, it will make more sense, and yet others say the best use for used paper is to incinerate it in a clean-burn unit to produce energy. This one will run and run…

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