Glossary

Acid Free
Paper with no acidity, but slightly alkaline, making it resistant to premature ageing in an acidic environment.

Brightness
The reflection of paper when measured under a specially calibrated wave of blue light. Many factors affect brightness, including the degree of bleaching of pulp, addition of chemicals such as titanium and fluorescent dyes.

Broke
Paper or board discarded during the manufacturing process, which is then repulped for reuse in the paper making process.

Bulk
A measurement of sheet thickness obtained by dividing the thickness of paper, in micrometres, by its grammage.

Calender
Where paper is passed through an assembly of calender rolls at the end of the paper machine, increasing the smoothness and gloss of the paper surface.

Caliper
Refers to the thickness of paper, generally expressed in micrometres (microns).

Cellulose Fibre
The fibrous materials remaining after the non-fibrous components of wood have been removed by pulping and bleaching operations used in making paper.

Chemical Pulp
Pulp obtained by cooking wood with solutions of various chemicals, usually under pressure and temperature. The principal chemical processes are the sulphite, sulphate (kraft) and soda processes.

CIE Whiteness
An internationally-recognised standard of paper brightness developed in Europe by the Centre Internationale d'Eclairage (CIE).

Conditioning
Allowing paper to adjust to a new room temperature and humidity before use, so that its moisture content is equal to the atmospheric moisture content. Conditioning assists optimum performance on press.

Converting Paper
Paper converted by a separate operation to produce a paper of different characteristics, or to produce a product quite distinct from the original paper. For example, producing envelopes, paper bags, or converting reels to sheets.

Cross-Direction (CD)
Perpendicular to the direction the web travels along the paper machine.

Curl
Waviness or curvatures which can occur at the paper mill, the printer’s storeroom, on the printing press, or in the bindery. Curl is usually associated with the humidity i.e., improper balance of moisture within the sheet, or uneven drying coming off press. Curl can also be the result of fibre orientation within the sheet, internal stresses, improper refining of pulp, or mechanical stresses during manufacture or printing.

Dandy Roll
A wire cylinder used in papermaking process to create effects such as laid lines and watermarks.

Deckle
The untrimmed edge of paper as it comes off the machine. The deckle also determines how wide the paper on a particular machine will be.

Density
Density generally is the ratio of the weight of paper to the volume (ie high density paper has a high weight to volume ratio).

Dimensional Stability
Paper or board may change in its dimension and flatness with variation in its moisture content. It is termed dimensionally stable when such changes are of a low order.

Embossed
A finish imparted to paper by means of raised or depressed engravings on steel rolls so as to leave a visible surface design on the paper. Normally a conversion process.

Formation
The manner in which the fibres of a sheet of paper or board are distributed and intermixed to constitute the sheet.

Furnish
The specific mixture of raw materials, both pulp and chemicals, from which a particular grade is manufactured.

Ghosting
A printed image on the reverse side of a sheet caused by the vaporisation of the ink solvent.

Gloss
Gloss is the surface reflectance value at a given angle. The greater the value the greater the surface of Gloss.

Grain
The direction in which the majority of the fibres are aligned. Long grain is synonymous with "machine direction" and short grain with "cross direction".

Grammage (GSM)
Weight per unit of paper ie basis weight in grams per square metre.

Hickies
Specks of dust or dirt adhering to the printing plate or blanket causing spots of colour with a halo around them in print.

Humidity
The moisture condition of the air. Relative humidity is the percent of moisture relative to the maximum which air at any given temperature can retain without precipitation.

Intaglio
A printing process where the image is etched below the surface of the plate, ink fills these grooves and then the sheet is printed. Gravure is a common example of this process.

Internal Bond Strength
A measure of the internal strength of paper and paperboard. Also, the bond between body stock and coating as measured by Dennison's Graded Waxes. Low internal bond strength could lead to picking the clay from the paper when tacky inks are used.

Kraft Paper
A strong pulp produced by the sulphate process by digestion of wood with sodium hydroxide and sodium sulphide.

Laid
Papers with a ribbed appearance produced by a dandy roll with parallel wires.

Letterpress
Printing from a relief printing image of metal, rubber or plastic with a viscous ink direct to the paper.

Lignin
An organic compound which is the main non-cellulosic constituent of wood. It bonds the cellulose fibres together. During pulping, chemicals dissolve the lignin, thus releasing the cellulose fibres as pulp.

Long Fibre Pulp (LF)
A general term given to pulps produced from soft woods such as pine. The fibre length of the pulps is long compared with that of hardwood.

Machine Coating
Applying coating to paper while on the paper machine. Can be done by several processes, the most successful of which are the doctor coaters such as the “trailing blade coater” or the ”air-knife” method.

Machine Direction (MD)
The direction of the forward movement the web travels on the paper machine.

Machine Finish (MF)
Finish obtained while the paper is on the paper machine and expressed as MF. Different finishes are obtained by the number of times paper is passed through the rollers, either dry or wet.

Machine Glazed (MG)
The finish produces din glaze on the wire side of a sheet as it is passed in contact over a single, large diameter, steam-heated cylinder. The finish is commonly referred to as MG.

Mechanical Pulp
Pulp produced by separating fibres from wood by abrasive (grinding) mechanical action only. This pulp is usually called “groundwood” pulp and the fibre strength within the pulp can be varied by using stones of different surfaces. Pulp can also be produced from chips processed through refiners.

Moisture Content
The percentage of moisture found in paper.

Misregister
When printing more than one colour, the succeeding plate fails to register to the previous printed sheet.

Mottle (paper)
Non-uniform colour of a paper sheet, whether accidental or intentional.

Mottle (printing)
When a printed area, especially a solid area of colour, looks uneven or spotty due to varying degrees of the absorption of ink.

Newsprint
A generic term used to describe the type of paper used for the publication of newspapers, often produced from mechanical pulp.

Nominal Grammage
The aim grammage for a grade when conditioned at specified humidity and temperature.

Offset Lithography
A method of printing utilizing a lithographic plate where the images are ink receptive, while the remainder of the plate is water receptive. Ink is transferred from the plate to a rubber blanket on the printing press, which then transfers the image to paper.

Opacity
A property of paper preventing the "show-through" of printing, the opposite of transparency.

Out-of-Square
Paper which is trimmed incorrectly and the corners are not at right angles. This will result in difficulty on press as there is no accurate guide edge to work from for accurate register.

pH
Degree of acidity or alkalinity measured on a scale of 0 to 14 with h7 being the neutral point. pH is important in paper permanence, and also for the proper functioning of fountain solutions in offset printing.

Picking
When fibres in paper pull away from the surface during the printing process. This occurs when the tack or pull of the ink is greater than the surface strength of the paper.

Pin Holes
Small holes in paper due to fibres being drawn through the mesh of the wire by excessive suction. Small holes in paper caused by fine particles of sand or similar, when the paper is calendered, the particles are crushed and fall out leaving a hole.

Piping
A type of creasing or ribbing in paper due to irregular tension and drying.

Porosity
Property of containing connected air voids. The porosity of paper is evaluated by measuring the air permeability under standardised conditions.

Pulping
To remove lignin or mechanically grind in refiners in the first stage of transforming wood into paper.

Reel Set
Machine direction (MD) curl induced into paper or board when winding or reeling a web into a roll. Usually occurs near the core.

Set Off
When a printed image is accidentally transferred or smudged onto the back of the following printed sheet within a stack. This usually occurs if the ink has not had enough time to dry or if the sheets are stacked too high or too tightly.

Semi-Chemical Pulp
Pulp made using a combination of chemical and mechanical methods, and usually used for corrugated mediums. Wood chips are partially cooked in sodium sulphite and then reduced to fibre by the mechanical action of an abrasive mill. Its advantage is that it makes a relatively strong pulp from hardwoods.

Short Fibres (SF)
Refers to pulp made from hardwoods, (eg eucalypt) because of their short fibre length relative to the fibre length of softwood (eg short-fibred pulp).

Silk Screen
A form of printing where a frame or screen is stretched with silk material and ink is passed through the screen, under pressure, via a soft rubber blade onto the sheet below.

Size
A material added either to the stock or to the surface of the sheet that improves printing qualities and imparts water-resistance to the sheet. Commonly used sizes are starch and latex.

Smoothness
The texture of the surface of paper, also called "finish". Determined by measuring the time required for a given volume of air to flow between the surfaces of the paper sample and a piece of optically flat glass under standard loading conditions.

Stiffness
Rigidity, resistance to bending, inflexibility.

Strike-through
In printing, the ink soaks through the sheet of paper to the reverse side. This is related to the absorbency of the paper and consistency of the ink.

Surface Sized
Paper that has been treated with starch or other sizing material at the size press of the paper machine. Surface sizing improves printing qualities and imparts water-resistance to the sheet.

Tensile Strength
Tensile strength measures the amount of force required to break a strip of paper. Tensile is important where high stresses are applied to the paper during processing.

Top Side
Paper web side that was not in contact with the fourdrinier wire during manufacture. Also termed "felt side".

Two Sidedness
Difference in properties between two sides of the same sheet, (ie front and back) in colour, formation or finish.

Watermark
Design formed among the fibres of a sheet as a result of the wet paper web coming into contact with the pattern of the dandy roll. The paper becomes thinner and more translucent where the fibres are displaced by the raised design.

Wire Mark
Traditionally, wire was sewn onto the dandy roll to form a pattern, logo or signature. Today, we utilise electrotype, the design of which is created by computer, engraved into bee's wax and immersed into an electrolysis bath. The resultant electrotype is coated with solder and affixed to the dandy roll using a soldering iron. A wire mark sits proud of the dandy roll and produces a mark which is lighter than the background.

Wire Side
The side of the sheet of paper which was originally in contact with the fourdrinier wire during the papermaking process.

Woodfree
Paper made entirely from chemical pulps, (eg kraft pulps) as distinct from papers incorporating mechanical pulp or groundwood. Usually applied to fine papers.