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Friday, November 26, 2010

Papermaking

Papermaking is the process of making paper, a substance which is used ubiquitously today for writing and packaging.
In papermaking a dilute suspension of fibers in water is drained through a screen, so that a mat of randomly interwoven fibers is laid down. Water is removed from this mat of fibers by pressing and drying to make paper. Most paper is made from wood pulp, but other fiber sources such as cotton and textiles may be used.

History of paper

Hemp wrapping paper, China, circa 100 BCE.
Papermaking is known to have been traced back to China about 105 CE, when Cai Lun, an official attached to the Imperial court during the Han Dynasty (202 BCE-220 CE), created a sheet of paper using mulberry and other bast fibres along with fishnets, old rags, and hemp waste.  However a recent archaeological discovery has been reported from near Dunhuang of paper with writing on it dating from 8 BCE, while paper had been used in China for wrapping and padding since the 2nd century BCE.Paper used as a writing medium became widespread by the 3rd century, and by the 6th century toilet paper was starting to be used in China as well. During the Tang Dynasty (618-907 CE) paper was folded and sewn into square bags to preserve the flavor of tea, while the later Song Dynasty (960-1279 CE) was the first government on Earth to issue paper-printed money.
In the 8th century, paper spread to the Islamic world, where the rudimentary and laborious process of papermaking was refined and machinery was designed for bulk manufacturing of paper. Production began in Baghdad under the supervision of the Grand Vizier Ja'far ibn Yahya, they invented a method to make a thicker sheet of paper. This helped transform papermaking from an art into a major industry. The earliest use of water-powered mills in paper production, specifically the use of pulp mills for preparing the pulp for papermaking, dates back to Samarkand in the 8th century. The earliest references to paper mills also come from the medieval Islamic world, where they were first noted in the 9th century by Arabic geographers in Damascus Papermaking was diffused across the Islamic world, from where it was diffused further west into Europe.
Paper is recorded as being manufactured in both Italy and Germany by 1400, just about the time when the woodcut printmaking technique was transferred from fabric to paper in the old master print and popular prints. Modern papermaking began in the early 19th century in Europe with the development of the Fourdrinier machine, which produces a continuous roll of paper rather than individual sheets. These machines have become very large, up to 500 feet (~150 m) in length, producing a sheet 400 inches (~10 m) wide, and operating at speeds of over 60 mph (100 km/h). In 1844, both Canadian inventor Charles Fenerty and German inventor F.G. Keller had invented the machine and process for pulping wood for the use in papermaking. This would end the nearly 2000-year use of pulped rags and start a new era for the production of newsprint and eventually almost all paper out of pulped wood.

Manual papermaking

Papermaking, regardless of the scale on which it is done, involves making a dilute suspension of fibers in water and allowing this suspension to drain through a screen so that a mat of randomly interwoven fibers is laid down. Water is removed from this mat of fibers by pressing and drying to make paper.


The art of papermaking. Medieval festival at Monselice.
First the fibers are suspended in water to form a slurry in a large vat. The mold is a wire screen in a wooden frame (somewhat similar to an old window screen), which is used to scoop some of the slurry out of the vat. The slurry in the screen mold is sloshed around the mold until it forms a uniform thin coating. The fibers are allowed to settle and the water to drain. When the fibers have stabilized in place but are still damp, they are turned out onto a felt sheet which was generally made of an animal product such as wool or rabbit fur, and the screen mold immediately reused. Layers of paper and felt build up in a pile (called a 'post') then a weight is placed on top to press out excess water and keep the paper fibers flat and tight. The sheets are then removed from the post and hung or laid out to dry. A step-by-step procedure for making paper with readily available materials can be found online.
When the paper pages are dry, they are frequently run between rollers (calendered) to produce a harder writing surface. Papers may be sized with gelatin or similar to bind the fibres into the sheet. Papers can be made with different surfaces depending on their intended purpose. Paper intended for printing or writing with ink is fairly hard, while paper to be used for water color, for instance, is heavily sized, and can be fairly soft.
The wooden frame is called a "deckle". The deckle leaves the edges of the paper slightly irregular and wavy, called "deckle edges", one of the indications that the paper was made by hand. Deckle-edged paper is occasionally mechanically imitated today to create the impression of old-fashioned luxury. The impressions in paper caused by the wires in the screen that run sideways are called "laid lines" and the impressions made, usually from top to bottom, by the wires holding the sideways wires together are called "chain lines". Watermarks are created by weaving a design into the wires in the mold. This is essentially true of Oriental molds made of other substances, such as bamboo. Hand-made paper generally folds and tears more evenly along the laid lines.
Hand-made paper is also prepared in laboratories to study papermaking and to check in paper mills the quality of the production process. The "handsheets" made according to TAPPI Standard T 205 are circular sheets 15.9 cm (6.25 in) in diameter and are tested on paper characteristics as paper brightness, strength, degree of sizing.

Industrial papermaking

 Papermachine
 Paper mill and Pulp and paper industry
A modern paper mill is divided into several sections, roughly corresponding to the processes involved in making hand-made paper. Pulp is refined and mixed in water with other additives to make a pulp slurry, the headbox of the papermachine (Fourdrinier machine) distributes the slurry onto a moving continuous screen, water drains from the slurry (by gravity or under vacuum), the wet paper sheet goes through presses and dries and is finally rolled into large rolls, often weighing several tons.
Another type of papermachine makes use of a cylinder mold that rotates while partially immersed in a vat of dilute pulp. The pulp is picked up by the wire and covers the mold as it rises out of the vat. A couch roller is pressed against the mold to smooth out the pulp, and picks the wet sheet off of the mold.

History of paper sheet production

 Paper sizes
 Bookbinding
Folio - In the beginning of Western papermaking, paper size was fairly standard. A page of paper is referred to as a leaf. When a leaf was printed on without being folded, the size was referred to as folio (meaning leaf). It was roughly equal to the size of a small newspaper sheet. ("Folio" can also refer to other sizes - see paper sizes.)
Quarto - A Folio folded once produces two leaves (or four pages), and the size of these leaves was referred to as quarto (4to) (about 230 x 280 mm).
Octavo - If the original sheet was folded in half again, the result was eight pages, referred to as octavo (8vo), which is roughly the size of an average modern novel. An octavo folding produces four leaves; the first two and the second two will be joined at the top by the first fold. The top edge is usually trimmed to make it possible to look freely at each side of the leaf. Sometimes books are found that have not been trimmed on the top, and these pages are referred to as unopened.
An octavo book produces a printing puzzle. The paper is first printed before folding and thus pages 8 and 1 are printed right-side-up on the bottom of the sheet, and pages 4 and 5 are printed upside-down on the top of the same side of the paper. On the opposite side, pages 2 and 7 are printed right-side-up on the bottom of the sheet, and pages 6 and 3 are printed upside-down on the top of the sheet. When the paper is folded twice and the folds trimmed, the pages fall into proper order.
Sixteen-mo - Smaller books are produced by folding the leaves again to produce 16 pages, known as a sixteen-mo (16mo) (originally sextodecimo). Other folding arrangements produce yet smaller books such as the thirty-two-mo (32mo) (duo et tricensimo).
Octavo bookbinding - When a standard-sized octavo book is produced by twice folding a large leaf, two leaves joined at the top will be contained in the resulting fold (which ends up in the gulley between the pages). This group of eight numberable pages is called a signature or a gathering. Traditionally, printed signatures were stacked on top of each other in a sewing frame and each signature was sewn through the inner fold to the signature on top of it. The sewing ran around leather bands or fabric tapes along the backs of the signatures to stabilize the pile of signatures. The leather bands originally used in the West to stabilize the backs of sewn books appear as a number of ridges under the leather on the spine of leather books. The ends of the leather strips or fabric bands were sewn or glued onto the cover boards and reinforced the hinging of the book in its covers.
Standardisation ISO sizes - While opinions and speculation abound on exact reasons for standardized paper sizes, the most revealing feature of popular sizes (such as Letter and ISO 216 sizes) is that they conform not to some arbitrary device dimension, but that the length of the paper is chosen to be the width of the page times the square root of 2. This feature allowed for a large page to be cut in half and the resulting 2 pages to have the same aspect ratio as the original piece (just with half the size). Repeated cuts can be made to reduce the entire sheet to one size of pages without wasted paper. This format was formalized by ISO 216 however such logic dictated efficient paper sizes long before the ISO was created. For example, traditional 8.5"x11" Letter paper is within a few millimeters of A4 paper (ISO 216) dimensions. While paper sizes "may" have been chosen based on the size of original frames, the frames themselves were chosen to make page reduction efficient without distorting the aspect ratio of the pages regardless of final size chosen. That said, there are paper sizes that do not conform to this idea when specific applications are needed.
Vatmen paper - Vatmen Paper was a type of paper made in the Netherlands that was 17 inches (~43 cm) wide and 44 inches (~112 cm) long. 44 inches was (reputedly) chosen because that is how far the papermaker could stretch his arm. A single vatman can generally handle a mold and deckle which produce up to a 25" wide sheet.


(sorce:wikipedia)

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