Glossary

'Clean Hands' Process:
A clean hands process in digital printing refers to ink changes on press that does not require any direct contact with the ink. A clean hands process differs from the process of changing ink on an offset press, which must be done manually by the machine minder.

Coated Paper
A wide variety of papers that have undergone coating to impart increased degrees of gloss, ink holdout, brightness, and smoothness. Enamel papers are high-gloss papers with high bulk and opacity and are ideal for offset printing. In digital printing specialist coated papers are developed that provide ideal performance for the different digital printing techniques. Commercial digital printers will usually stock the papers specifically developed for the press that they run.

Color Seperation
A means of dividing a full color photograph into four separate components, corresponding to the four primary colors used in process color printing—cyan, magenta, yellow, and black. Process color printing involves overprinting halftone dots of each of these four colors in varying densities, the various combinations producing the wide range of reproducible colors. Consequently, a different printing plate needs to be made of each color and this, in turn, requires separate negatives or positives. (The term color separation refers to both the process and the products of that process.) The process of color separation can be accomplished photographically, electronically, or on the desktop.

CMYK
CMYK refers to the four inks used in color printing: cyan, magenta, yellow, and key (black). The reason for black ink being referred to as key is because in four-color printing, cyan, magenta, and yellow printing plates are carefully keyed, or aligned, with the key of the black, black being the key plate.

Drum
A generic term for any printing press cylinder, such as a plate cylinder, blanket cylinder, impression cylinder, or gravure cylinder.

Dye
Dyes are extremely tiny particles of colour dissolved in water or some other solvent. These dyes are then dissolved in the ink vehicle.

Fountain Solution
Fountain solution is a mixture of water and other chemicals distributed by the dampening system on an offset printing press which works to desensitize the non-image areas of the plate, rendering them ink-repellent.

Laser
An acronym for Light Amplification by Stimulated Emission of Radiation. A laser is essentially a thin, intense beam of coherent light. It differs from light emitted by conventional light bulbs in that traditional light is in'coherent; light waves are radiated in all directions independently of each other, and the crests and troughs of the wave do not coincide with each other and therefore possess little energy. In a laser, all the light waves are emitted in the same direction and with their crests and troughs aligned with each other. The beam thus has a great deal of energy. The light rays, as they travel along the beam, are kept as close to being parallel with each other as possible and, as a result, the waves diverge very slightly.

Multi-Pass Printing
Multi-pass printing refers to printing that involves multiple 'passes' under a single drum. The printing drum can only dispense one type of ink at a time. To produce full-color results, a sheet of paper has to pass beneath the drum four separate times (CMYK) to reproduce each colour.

Pigment
Pigments are based on microscopic particles of colour. Unlike dyes, they cannot be completely dissolved in water (or other solvent), so the pigment particles need to be small enough to pass through the desired nozzle diameter. The primary advantage of pigment-based inkjet inks is their permanence; Independent tests have estimated that prints made with pigment-based inks can keep their colour for up to 80 or 100 years, depending on the environmental conditions. Note however that pigment-based inks achieve their permanence only when used on compatible substrates.

Plate
The plate is the basic image-carrying surface in a printing process, which can be made of a variety of substances, such as various metals (as those used in letterpress and lithography), rubber, or plastic (such as those used in flexography). The image areas of a printing plate may either be raised above the non-image areas (such as in letterpress or flexography) or on the same plane as the non-image areas (as in lithography). The exact nature, composition, and method of platemaking depend on the printing process to be utilized.

Prepress
Generally speaking, the term prepress includes all the steps required to transform an original artwork into a state that is ready for reproduction by printing. Prepress includes all the steps towards generating a print ready artwork. Generally, a critical step in this process is colour separation.

RGB
The RGB color model is an additive color model in which red, green and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue. The main purpose of the RGB color model is for the sensing, representation and display of digital images.

Screen Printing
A form of printing in which a thick paste ink is forced through a stencil attached to a finely-woven mesh screen, transferring ink to the desired substrate in those areas not covered by the stencil. Screen printing, also known as screen process and serigraphy, is used to print almost any surface imaginable, from T-shirts and other textiles to posters to signs to tablecloths to shower curtains to leather goods.

Sheetfed Press
Sheetfed presses print on sheets, have a feeder system consisting of drawers and/or a pallet of paper, and print on both sides of the paper (duplex print/perfecter), printed sheets are collected in a stacker mainly for paper printing.

Single-Pass Printing
Single-pass printing refers to printing that produces a completed copy of an image in a single 'pass.' In other words, the page is fed into the printer and all of the ink is applied to the media at once.

Uncoated paper
Paper which has not had a coating applied (see coating). Uncoated papers produce a specific print finish due to the fact that the ink - when printed offset, digital offset, inkjet or Riso - will sink into the paper as opposed to sitting onto of the paper surface as is the case with coated papers. Ink drying on an uncoated paper is subject to dot gain. Dot gain means that each ink droplet expands in contact with the uncoated paper before it dries. This can lead to printed images retaining less detail in the shadows and highlights.

Webfed Press
Webfed presses print on rolls, often referred to as a web the feeder system (unwinder) feeds the paper through continuously in most cases, print on one side of the substrate (simplex) printed rolls can be collected on a rewinder or cut into sheets.