Printing is a means of graphic communications and the reproduction of quantities of images, which can be seen or perceived visually.
Web presses are used almost exclusively by gravure and have been a dominant factor in lithographic printing since 1954. Papermaking was invented in China. Five major printing processes use four different methods of printing. Letterpress and flexography are relief, gravure is intaglio, lithography is planographic, and screen is porous or stencil printing. The following are the basic printing process steps:
- Sorting and preparing the copy elements for reproduction
- The prepress operations of making a design or layout for reproduction, converting the text and assembling them in on a flat for platemaking
- Binding and Finishing
- Finishing Distribution
Letterpress is the oldest method of printing, with equipment for short, medium, or long runs. Printed by the relief method from cast Meta type or plates, duplicate plates or photopolymer plates on which the image or printing areas are raised above the non-printing areas. Much time is consumed in make-ready, or building up of the press form so that both the light and heavy areas print with the correct impression. There are four types of presses: platen, flatbed cylinder, rotary and belt.
- Flexography-a form of rotary web letterpress using flexible rubber or photopolymer plates and fast-drying solvent or water-based inks fed from an anilox inking system. Major process for printing milk containers, gift-wraps, and shopping bags. Used highly in packaging industry.
- Thermography-process which creates special embossed effects in printing such as stationery, invitations, greeting cards and paper decoration.
- Gravure-example of intaglio printing that uses a sunk or depressed surface for the image. Three types of gravure include conventional, variable area-variable depth, and direct transfer to variable area. Variable area gravure is used mainly for packaging printing.
- Steel-die engraving-intaglio process in which the die is hand or machine cut, or chemically etched to hold ink.
- Offset lithography-most popular, uses the planographic method. Transferring the image from the pate to a rubber blanket before transfer to the paper is called the offset principle. Major advantage is that the soft rubber surface of the blanket creates a clearer impression on a wide variety of paper surfaces and other materials with both rough and smooth textures with a minimum of press make-ready.
- Collotype-Screenless printing; photo gelatin printing reproduces illustrations in continuous tone or without halftone dots. Collotype is a reproduction process, which uses bichromated gelatin as a printing medium and is capable of high-quality reproduction in runs for 100 to 5,000. The main advantages are high resolution, no screen moiré and greater purity of color especially in tints and middle tones.
- Screen printing/silkscreen-employs a porous screen of fine silk, Nylon, Dacron or stainless steel mounted on a frame. Versatility is the principal advantage.
- Electronic and ink-jet printing-pressure less and plateless printing processes that use computers, electronics, electrostatics/special toners, and inks to produce images.
- Copying and duplicating-reprography
- Electrophotography-based on electrostatic transfer of toner to and from a charged photoconductor surface.
- Offset duplicator-when copies in quantities up to 10,000 are needed, the most economical printing method is the offset duplicator.
- Stencil duplicator/mimeograph-forcing ink through a stencil prepared on a typewriter, or spark discharge, produces copies of acceptable quality on plain paper.
- Spirit duplicator-master can be made to print more than one color at the same time using special carbon papers, which contain soluble dyed resins of different colors.
Typefaces are usually available in 6- to 72-pint, with a complete font in each size. A font is defined as a complete assortment of any one size and style of type containing all the characters for setting ordinary composition. The Classifications of typefaces fall under either Oldstyle, Modern, Square Serif, Sans Serif, Script, Text Letters, and Decorative types.
Readability is the ease of reading a printed page, whereas legibility refers to the speed with which each letter or word can be recognized. Readability refers to the type arrangement; legibility is concerned with type design. When selecting a typeface, you must consider the texture and finish of paper, color of ink, typeface, size of type, line length, line spacing, etc.
Letterspacing is the amount of space used between letters, negative or positive, either for readability, aesthetics or to fill a certain area. Negative letterspacing involves the removal of space between letters individually (kerning) or between all letters equally (called white space reduction or tracking). Line spacing is the amount of space between lines, which is known as leading and is always expressed in points or fractions of a point.
Images that are not assembled together must be cross-referenced for easy identification in an operation called keying.
- Cast metal or hot type composition, typewriter or strike-on composition (sometimes called cold type), photographic typesetting, and electronic printing.
- Photographic typesetting
- Scaling-changing the size of the original without changing the ratio of the dimensions.
- Cropping-to eliminate certain areas from the picture.
- Opaquing-ownership transparency minimizes role of print in the back of the sheet. Its value is reported as a percentage of transmitted light against a completely opaque body. Common units are General Electric and Photo Volt.