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Onion skin paper
A lightweight writing paper. It has been used for writing especially airmail letters, typing and making carbon copies with a typewriter. It generally has a weight of less than 20gsm and will be a chemical and/or rag pulp with a smooth, glazed, semitransparent and cockled finish.

Optical Brightener
Optical brighteners are chemicals added to the pulp to make the formed paper appear whiter. Generally they are fluorescent synthetic dyes that absorb visible and ultraviolet light and then re-emit it at a higher wavelength often in the violet or bluish end of the spectrum, therefore adding brightness to the paper.

Organosolv pulp
A pulping process in which organic chemicals, such as ethanol, methanol, acetone, butanol, ascetic acid and formic acid are used to solubilize lignin. It was first discovered by Theodore Kleinert in 1971. Organosolv pulping offers the advantage of higher pulp yields than sulphate pulping, less water and odour pollution, recoverable usable lignin, recoverable carbohydrates for ethanol production and easy chemical recovery; however it does produce slightly weaker pulp.

Oxygen bleaching
An oxidizing process in which the wood or pulp is exposed to oxygen in an alkali medium to oxidize and degrade the lignin. In the bleaching sequence it is referred to by the letter ‘O’. The alkali used is compatible with the Kraft process, and can be recovered in a recovery boiler, thereby reducing the overall amount of chemicals required. Oxygen bleaching was developed by Nikitin and Akim in 1952 in the USSR and was commercialized in the late 1960s, and in the 1970s the first displacement bleaching plant was operated. It is also referred to as oxygen delignification.

Ozone bleaching
An oxidizing bleaching/delignification process introduced in the 1990s. The process involves exposing the pulp or wood to ozone at low pH, 2 to 4, at temperatures of 50°C to 60°C. Ozone is used in both TCF and ECF bleaching and has the advantages of reduced chemicals, fast action and high brightness. As the ozone process is not selective to lignin care should be taken not to damage the cellulose. In the bleaching sequence it is referred to by the letter ‘Z’.

Papermakers alum
Aluminium sulphate which was introduced in 1876 as a replacement to Aluminium Potassium Sulphate. It was used for sizing and water purifying.

Paper mulberry
The Japanese name for paper mulberry is Kozo. The bast fibres of the paper mulberry have been used in papermaking in Asia for centuries. The fibres are very long and strong meaning that the fibres may be added to a wide variety of other fibre types, and the resulting paper used in a wide variety of uses, from writing, painting, calligraphy, folding screens, umbrellas, sliding doors, toys, lanterns etc.

A thin writing material made of the prepared hide of a calf, goat or sheep. Parchment was used in Europe until the introduction of paper in the Middle Ages. Parchment is made through first soaking, then retting the skin and then stretching and scrapping with a curved blade to remove all of the remaining flesh and hair. It is then stretched and dried, and may have the surface treated with pumice powder, starches, albumen, flour or milk to improve the whiteness and writing properties. As parchment is untanned, unlike leather, it is very susceptible to any changes in moisture.

Parchment bond
A paper made of over beaten rag or chemical pulp. It is known for its durability and velvety surface.

Parchment paper
A paper created by passing an unsized rag, or chemical pulp, paper through a bath of sulfuric acid or zinc chloride, and then washing it thoroughly. The acid hydrolyses the cellulose and leaves the paper heat, grease and moisture resistant as well as being translucent. It is frequently used in baking where its heat resistance and non-stick characteristics are useful.

Platen calendared
Paper that is platen calendered has been cut and pressed between metal in a press.

A layer of paper.

Prussian blue
Developed in Berlin in 1706 by the paint maker Johan Diesbach, Prussian blue was one of the first synthetic pigments . It is a dark blue colour. The earliest known usage of the pigment in art was in 1710, and by the 1720s it was widely available. Prussian blue is an oxidized iron cyanide salt that has the formula Fe7(CN)18.

The mix of paper fibre and water after the fibres have been defibrillated and dispersed.

The first papers made in Europe were made from used clothing rags. These clothes were made of cotton, linen, and ramie, and today the term rag means the fibres from cotton, linen and ramie. These fibres are all high in cellulose and low in lignin and make some of the highest quality papers.

Rag content paper
Paper with a content of rag.

The noise produced when sheet of paper is shaken. Its presence can be indicative of stiffness or rigidity; however its absence is required for certain usages.

Depending on the type of paper, a name for a unit of 480 or 500 sheets of paper.

Ream weight
The weight of a ream of paper of particular type and size.

Retention aids
A chemical that helps the pulp retain certain fillers, sizes, brightening agents etc. when it is formed into a sheet, without affecting the water drainage properties. With the use of retention aids, fewer chemical additives are wasted in the process of forming the sheet. Examples of retention aids are polyacrimide, polyethyleneimine or bentonite.

Recycled paper
Paper that has been made from waste paper. The paper used in recycled paper is either mill broke, trimmings or scrap from papermaking, pre-consumer waste, paper which has left the mill but is unused, or post-consumer waste which is paper that has left the mill and been used. The paper for recycling is first broken down, heated, strained, deinked, bleached and then formed into a pulp to be remade into paper again. Justus Claproth first developed deinking in 1774, and then in 1801 Mathias Koop patented a way of deinking and recycling paper. In the 1950s froth flotation started to be used to deink paper. Paper fibres can usually be recycled about five or six times before the fibres all become too short to be recycled again.

A device for defibrillating wood into pulp. The two most common types are the disc refiner and the cone refiner.

Rice paper
Fine oriental paper, which is actually not made entirely of rice, but a mix of rice and any number of longer fibres.

A derivative of resin extracted from coniferous trees. It has been used with alum in paper sizing since 1807, and by the mid-19th century was in common usage. Rosin has a hydrophobic and hydrophilic end to the molecule, and is precipitated onto the fibres by alum. The hydrophobic portion of the molecule reacts with ink preventing it from being absorbed straight into the paper fibres. Sizing most effectively occurs at pH 4-5.5 which leads to acidic paper that will increase in acidity and weakness over time. Papers sized with alum-rosin tend to become acidic through hydrolysis.

Rosin wax size
An aqueous emulsion of a paraffin or microcrystalline wax and rosin used in sizing. It is often anionic (negatively charged).

Security thread
An anti-counterfeiting measure used in passports and bank notes. It consists of a fine ribbon of plastic or metal that has been woven or enmeshed into the surrounding paper fibres.

SemiChemical pulping
A pulping process in which the wood chips are mildly cooked in a chemical pulping solution, such as in soda, sulphite or sulphate pulping, before being ground in a disc refiner. Neutral sulphite is a common method used in semi chemical pulping, in which sodium sulphite combined with an alkali salt is used. Semichemical pulping uses less chemicals and less cooking time than chemical pulping, while having a higher pulp yield. The pulp yield is 60-80%, however much of the lignin remains in the pulp.

Shadow watermark
This is a watermark that is created through a recessed area in the dandy roll pressing onto the still wet pulp. Since it is recessed it draws more pulp into the void, and through transmitted light this area appears darker. This technique is often used in combination with raised area to produce a multi-tonal watermark that is often seen in security papers.

Sizing is the addition of certain chemicals to paper to reduce the absorbency and improve the writing and printing properties of the paper. There are two methods of sizing: internal sizing and surface sizing. Internal sizing is also sometimes known as engine sizing, while external sizing is sometimes known as tub sizing, as traditionally the formed sheet was dipped into a tub of sizing agent. Common chemicals used for sizing include gelatine, alum-rosin, starch, alkyl ketene dimers and alkyl succinic anhydride.

Soda Pulp Process
A chemical process involving cooking wood pulp in sodium hydroxide or a caustic soda solution, to create pulp. The first mill using this method was started in the USA in 1860. This process has the advantage of being able to better handle the silicate found in agricultural waste, such as straw and bagasse. The pulp produced from this method is weaker than other chemical pulping methods, producing paper with low tear strength, and used large amounts of the then expensive sodium hydroxide, leading to the development of the chemically cheaper and stronger sulphate process. After the invention of sulphate pulping in 1879 many soda mills converted to sulphate mills. It has a 40-55% pulp yield depending on the wood used.

Sodium hydroxide
Discovered in 1807 by Humphrey Davy, it has been used as an alkali wash and in the white liquors of Kraft pulping. In the bleaching sequence, an extraction with sodium hydroxide is referred to in shorthand by the letter ‘E’. It has the chemical formula of NaOH. It is also known as caustic soda.

Sodium hypochlorite
A chlorine based liquid bleach with the chemical formula NaClO, invented in 1785 by Claude Berthollet in France. It was replaced by the cheaper calcium hypochlorite discovered by Charles Tennant in 1798. It is sometimes referred to as Eau de Javel.

Wood from the gymnosperm order of trees. Although generally softer than hardwoods, there are examples of softwoods that are harder than hardwoods and vice versa. Softwoods have fewer vessel elements and generally longer fibre length than hardwoods. Examples of softwoods are pines, cedars, spruce, douglas fir and yew.

An early machine for fibrillating rags into pulp, usually water powered. It beat the rags with hammers striking down into mortars. It was replaced with the Hollander beater which was invented in Holland around 1680.

An agricultural by product, consisting of the dry stalks, of harvested cereal plants. Matthias Koop produced paper from straw in 1800, and after that was used as in pulp, although not as the primary fibre. During WW1 and WW2 it was used as a replacement for esparto in British paper mills.

Sulphate Process
This process is also commonly known as the Kraft process. The name Kraft comes from the German word for strong as the paper produced by this process is stronger due to the cellulose chain being less likely to be broken than with the competing acidic sulphite process. This process involves the treatment of wood pulp with a mixture of sodium hydroxide and sodium sulphide to break the bonds between the lignin and cellulose and produce a cellulose pulp. First invented in 1879, the first mill to use this process was started in 1890 in Sweden. In the early 1930s the Tomlinson recovery boiler was invented allowing the recovery of the inorganic pulping chemicals. As a result of this invention, sulphate processed papers started to exceed sulphite papers in the 1940s and 1950s. Compared to the sulphite process, sulphate pulp is generally stronger, less acidic, can use a wider range of woods, requires extra refining and is harder to bleach. Sulphate pulping has a 45-55% pulp yield.

Sulphite Process
A chemical process in which wood chips are treated to produce cellulose and lignin is extracted. The cellulose is produced through the treatment of wood pulp with sulphurous acid in large high pressure vessels called digesters. This process was invented by American Benjamin Tilghman, and in 1874 the first commercial sulphite mill was built in Sweden. By 1900 it was the dominant papermaking process. Sulphite pulp has an equal pulp yield to sulphate pulping and the pulp is easier to bleach, however due to the acidic treatment some of the cellulose is hydrolyzed making generally weaker and more acidic paper. The sulphite process cannot process barks, resinous softwoods and tannin containing hardwoods. Until the invention of the Tomlinson recovery boiler in the 1930s sulphite pulp was the predominant method of forming chemical pulp. Sulphite mills currently produce only about 6% of chemical pulp globally. Sulphite pulping has a 40-50% pulp yield.

Paper that has been supercalendered has passed through alternating metal and fibre covered rollers and are known for their highly glazed surface that is used in publishing.

Surface sizing
The application of sizing to the surface of the already formed sheet. Starches and synthetic sizing agents are the most common forms of surface size used. Papers can be surface sized with starch at the sizing press on a papermaking machine to increase its printing and writing properties, even if it has already been internally sized. It is also called tub sizing.

Synthetic ultramarine
A deep blue created by Jean-Baptiste Guimet in 1826, and then commercially sold in 1828, as a replacement for the very expensive traditional ultramarine derived from lapis lazuli.