Glossary
Ageing - The deterioration of paper properties with time. Sunlight and heat accelerate loss of strength and brightness.
Bleaching - Chemically treating a pulp to increase delignification (after the colour matter) so the pulp has a higher brightness.
Brightness - A measure of the reflectance of paper in the blue region of the light spectrum. On its own, brightness does not describe the colour of the paper. Brightness is sensitive to the UV content of the illumination if the paper contains fluorescent whitening agent.
Bulk - Paper thickness. Sometimes used as the number of pages per inch (PPI).
Caliper - Thickness of paper measured in microns (1000microns = 1mm).
CIE Whiteness - A measure of the extent to which a white paper can be described as "blue-white". Whiteness is sensitive to the UV content of the illumination if the paper contains fluorescent whitening agent. Whiteness on its own is not sufficient to describe the colour of paper (i.e. two sheets with the same whiteness value may be quite different shades of white).
Chemical pulping - Chemical pulping removes most of the impurities such as lignin, resins, gums and other undesirable components of the wood so that the pulp is mainly cellulose fibre. Chemical pulping is done by cooking wood chips with solutions of various chemicals, usually under pressure and temperature. The principal chemical processes are the sulphite, sulphate (kraft) and soda processes.
Coating - A layer of minerals applied to one or both sides of paper or board to improve brightness, gloss and printability; the coating is held together and stuck to the paper by a binder.
Copier/Laser Papers - Lightweight grades of good quality and dimensionally stable papers used for copying correspondence and documents.
Digital Printing - Printing in which an image is applied to paper or another substrate directly from a digital file rather than using film and/or plates.
Fibre Source - Types and locations of fibrous raw materials.
FSC - Forest Stewardship Council. An international organisation promoting responsible forest management. FSC has developed principles for forest management which may be used for certifying the management of forest holdings, and a system of tracing, verifying and labelling timber and wood products which originate from FSC-certified forests.
Gloss - Gloss is the surface reflectance value at a given angle. The greater the value the greater the surface of gloss.
Grain - In machine-made papers, the direction in which the majority of the fibres are aligned, (ie. the machine direction). Long grain is synonymous with "machine direction" and short grain with "cross direction".
Grammage - The term used to denote the weight of paper or board; the measurement used is the weight of a single sheet of one square metre, expressed as gramme per square metre (gm2). The gramme weight of one square metre of a particular type of paper; a good comparative measure because it does not vary with sheet size.
Laser Papers - Papers with special coatings or hard finishes that are optimised for laser printers and copiers.
Lignin - An organic compound which is the main non-cellulosic constituent of wood and bonds the cellulose fibres together. During pulping, chemicals dissolve the lignin, thus releasing the cellulose fibres as pulp.
Machine Coating - Applying coating to paper on the paper machine on which the paper is made and can be done by several processes. The most successful are the doctor coaters such as the 'trailing blade coater' or the 'air-knife' method.
Mechanical Pulp - Pulp produced by separating fibres from wood by abrasive (grinding) mechanical action only, using no chemical. Fibre strength can be varied by using stones of different surfaces. Usually called "groundwood" pulp. Can be produced from chips processed through refiners, in which counter-rotating barred metal plates, very close together replace the grindstone.
Moisture Content - The amount of moisture in paper, normally ranging from 5% to 8%. Paper easily picks up or emits moisture to and from the surrounding environment.
Opacity - That property of paper which minimises the show-through of printing from the back side or the next sheet.
Optical Brighteners - Also called fluorescent whitening agents, these are used extensively to make very high bright, blue-white papers. They absorb invisible ultraviolet light and convert it to visible light on the blue/violet end of the spectrum.
pH - Degree of acidity or alkalinity measured on a scale of 0 to 14 with 7 being the neutral point. pH is important in paper permanence but also in proper functioning of fountain solutions in offset printing.
Porosity - The property of paper that allows the permeation of air, an important factor in ink penetration.
Pulping - To remove lignin or mechanically grind in refiners in the first stage of transforming wood into paper.
Runnability - Paper properties that affect the ability of the paper to run on the press.
Smoothness - The surface quality of a sheet of paper, related to the flatness of the sheet. Smoothness affects ink and toner receptivity. Smoothness is measured by the Sheffield scale and a higher value typically indicates a rougher sheet.
Stiffness - Rigidity, resistance to bending, inflexibility.
Woodfree - Pulp and paper that are made entirely from chemical pulps, (eg. kraft pulps) as distinct form papers incorporating mechanical pulp or groundwood. Usually applied to fine papers. Woodfree is an historical paper-making term shortened from "groundwood-free". However, when used in connection with finished paper products now widely available from office super stores etc, it understandably causes confusion amongst end consumers who wrongly assume it to mean the product thus described is literally woodfree and does not involve trees.
