Prepress Mod 2-pp

Module 2: Printing Processes

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Module 2: Printing Processes

Instructor: Doughlas Remy

Module 2: Printing Processes

Module Overview • • • • • • • • • • • • •

The U.S. printing industry Definition of printing Major printing processes (overview) Where’s the ink? Where’s the paper? Early relief printing Text and artwork before and after the invention of photography Flexography (relief) Planographic printing (offset litho) (major printing processes) Gravure (Intaglio) Screen printing (silkscreen, stencil) Digital (electronic) printing Spot colors and process colors Continuous tone vs. halftone

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What you should know about the U.S. printing industry • It has a very low profile. • It is composed mainly of small businesses. • It has revenues of about $1 billion annually. • It is the nation’s largest employer. (It employs nearly 1 million people, or 220,000 more than the auto industry.)

• There are nearly 100,000 printing establishments in the U.S. • Pre-press is considered to be a part of the printing industry. Source: http://www.wmrc.uiuc.edu/info/library_docs/manuals/printing/domestic.htm

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Definition Printing is basically the transfer of images from a source (usually printing plates) to a target surface (usually paper) through the application of a medium (usually ink). Sources

most common

Plates

(e.g., aluminum, polymer, rubber)

Type forms

(used in

letterpress)

Templates

(used in screen

printing)

Blocks

(made of wood, metal, lino, plastic, stone)

Jets

(used in inkjet printing)

Targets

Media

Paper Fabric Metal Plastic

Inks Toner s Dyes Paints

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Major Printing Processes

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Module 2: Printing Processes

Major Printing Processes • Relief (primarily flexography, which evolved from letterpress) • Planographic (offset lithography) • Gravure (aka Intaglio, Photogravure, Rotogravure) • Screen (aka silkscreen, stencil, serigraphy) • Digital (aka electronic)

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Module 2: Printing Processes

Major Printing Processes • Relief (primarily flexography, which evolved from letterpress) • Planographic (offset lithography) • Gravure (aka Intaglio, Photogravure, Rotogravure) • Screen (aka silkscreen, stencil, serigraphy) • Digital

In a category by itself because 1.it is for low-volume printing; and 2.its technology is so different from the others.

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Major Printing Processes • Relief (primarily flexography, which evolved from letterpress) • Planographic (offset lithography) • Gravure (aka Intaglio, Photogravure, Rotogravure) • Screen (aka silkscreen, stencil, serigraphy) • Digital Now a major printing process and growing exponentially. Its technology is very different from that of the first three on this list.

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Major Printing Processes • Relief (primarily flexography, which evolved from letterpress) • Planographic (offset lithography) • Gravure (aka Intaglio, Photogravure, Rotogravure) • Screen (aka silkscreen, stencil, serigraphy) • Digital

We will focus on the first three for now.

Module 2: Printing Processes

Major Printing Processes • Relief (primarily flexography, which evolved from letterpress) • Planographic (offset lithography) • Gravure (aka Intaglio, Photogravure, Rotogravure)

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Major Printing Processes: Where’s the ink? Where’s the paper?

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Where’s the ink? The first three—relief, planographic, and gravure—are easier to understand if we compare the location of the ink in these cross-sections of the printing plates used for each: Relief Planographic Gravure

• • •

Ink is on a raised surface. Ink is on a flat surface. Ink is in wells or reservoirs.

Relief (primarily flexography, which evolved from letterpress) Planographic (offset lithography) Gravure (aka Intaglio, Photogravure, Rotogravure)

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Where’s the paper? (1) 1. The paper may be attached to a flat surface, against which a type form or a printing plate is pressed. Note This way of placing the paper was a feature of the earliest printing methods and is rarely used today. (It’s very slow.)

lever attached to screw

type form

Wooden hand press (aka screw press), a reproduction of Gutenberg’s press.

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Where’s the paper? (1) Lever Press This was a later development, using the same principle of attaching the paper to a flat surface. Note that there is no screw.

A layer of oil-based ink is applied here, and then a roller arm (not shown here) pivots up to collect the ink and then rolls it onto the “chase,” which contains the relief image. The “chase” (relief image) Paper attached here.

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Where’s the paper? (2) 2. The paper may be attached to a cylinder, which then rotates as an inked type form passes beneath it. Note This way of placing the paper, like the previous one, was timeconsuming and was abandoned in favor of the last two methods (next slides).

Ink Rollers

Cylinder Letterpress Paper

Type form Impression Cylinder Press bed

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Where’s the paper? (3) 3. Sheets of paper pass between two flexible printing plates (attached to cylinders) that are carrying the image. Note This technology did not become possible until a means could be found for making the printing plate thin and flexible enough to attach to a cylinder.

Note The process of printing on both sides of the paper (recto and verso) is called “duplexing.”

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Where’s the paper? (4) 4. A continuous “web” of paper passes between two flexible printing plates (attached to cylinders) that are carrying the image.

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Where’s the paper? (4) Why “Web”?

The American Heritage Dictionary has 11 definitions of “web.” # 1: “A textile fabric, especially one being woven on a loom or in the process of being removed from it.” # 11: “A continuous roll of paper, as newsprint, in the process of manufacture in a paper machine or as it comes from the mill.

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Major Printing Processes • Relief (primarily flexography, which evolved from letterpress) • Planographic (offset lithography) • Gravure (aka Intaglio, Photogravure, Rotogravure) • Screen (aka silkscreen, stencil, serigraphy) • Digital

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Major Printing Processes: Early Relief Printing

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Relief: Letterpress – Historical overview Signet rings were first used in ancient Babylonia.

Modern signet rings

a wax seal

No further progress was made in the Western world until the Gutenberg era (15th century).

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Relief: Letterpress – Early Chinese printing Meanwhile, the Chinese were printing from wood blocks as early as the 2nd century A.D. This was made possible by their invention of paper in A.D. 105. Papyrus had been too fragile. Vellum* was too expensive.

*Vellum is a thin tissue taken from inside the hides of newly skinned animals.

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Relief: Letterpress – Early Chinese printing The Chinese developed movable type around the tenth century A.D., and were even doing two-color printing with it. By the 13th and 14th centuries, they had three-color and four-color printing. At first, they used clay type, but later developed metal (copper) type. Movable type was not as practical for the Chinese language as it was for European languages, because it required between 2000 and 40,000 separate characters.

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Relief: Letterpress – Early Western printing Earliest Western print technology grew up in the Rhine River Valley in the mid-fifteenth century and was probably not influenced by earlier developments in the Far East. Western printing technology

Eastern printing technology

Oil-based inks

Water-soluble inks

Mechanical presses derived from wine presses. Used movable metal type.

Paper pressed against wood block. Later: movable clay and metal type

Used pressure from edge of tray to hold type in place

Used clay or rods to hold type in place

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Relief: Letterpress – Early Western printing The first printing presses in the West were screw-type presses designed primarily to bring pressure on the printing form, which was placed face up in a flat bed.

Click here for photos of screw-type presses from the Museum of Printing Presses.

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Relief: Letterpress – Early Western printing Consider this: Letterpress printing from raised metal type was the primary means of mass communication for over 400 years.

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Relief: Letterpress—Later Developments

“Old Reliable,” platen letterpress, 19th century.

Later developments in the West: • In the 17th century, springs were added to the press to aid in lifting the platen rapidly. • Around 1800, iron began to be used in the construction of presses, and levers were substituted for the screws that brought the platen down onto the form. • The process was still slow (300 impressions per hour), but much larger forms could be used, so multiple pages could be printed simultaneously.

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Relief: Letterpress—Later Developments Cylinder Letterpress

Ink Rollers

Cylinders were not used in letterpress until the 19th century.

Paper

Type form Impression Cylinder Press bed

The ink rollers apply ink only to the raised areas. Then the ink is transferred to the paper, which is on the impression cylinder. Letterpress images can be sharp and crisp. However, the pressure of the plate or cylinder surface on the paper may also spread the ink slightly.

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Relief: Letterpress—Later Developments

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Relief: Letterpress

A cylinder letterpress

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Major Printing Processes: Relief Printing: Text and Artwork Before and After the Invention of

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Relief: Letterpress—Text and Artwork

Before the invention of photography and the development of modern printing techniques, the raised image in relief printing could only be produced in two ways: •For text: Metal type •For artwork: Engraving or etching. These techniques leave a flat, raised surface to which the ink is applied. Engraving is simply cutting away the areas that will not receive the ink. Etching involves making incisions on a plate that has been coated with an acid-resistant material, and then applying acid to the entire surface.

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Relief: Letterpress—Text and Artwork Note that artwork had to be in the form of either engravings or etchings if it was to be printed.

Wood engraving, 1830: View of Rochester with a Section of the Aqueduct

Etching by Jacques Callot, 1633: The Miseries of War.

In both techniques, the area that will not receive the ink is removed—either by direct cutting or by application of acid.

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Relief: Letterpress—Text and Artwork Electrotyping (first used in 1838) was a technique for making duplicate plates from original relief plates. To create an electrotype duplicate: 1.Make a mold of the original plate, using any one of various materials (copper, lead, zinc, etc.) 2.Place the mold in an electrolytic solution (e.g., copper sulfate and sulphuric acid). 3.Place a sheet of the same or a different metal in the solution, parallel to the mold. 4.Pass an electrical current through the solution. The mold acts as the cathode and the other metal sheet as an anode. Metal passes from the anode to adhere to the cathode (the mold). 5.Separate the newly-deposited layer of metal from the mold.

mold

metal sheet

tank containing electrolytic solution

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Relief Printing—Text and Artwork After the Invention of Photography After the invention of photography, it became possible to dispense with lead fonts and type forms altogether. Photographic transparencies could be used to make plates, and this led to the demise of letterpress. To understand platemaking from photographic

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Relief Printing—Text and Artwork After the Invention of Photography Halftone screens: •Physical screens (either glass plates or contact sheets), consisting of grids through which light may pass. •Placed between a photographic transparency and a photosensitive plate.

Glass plates

•Light passes differentially through the transparency and then through the halftone screen to the photosensitive plate. •The light reacts with the chemicals on the plate to produce areas that are receptive to ink. •These ink-receptive areas, if examined under a magnifying glass, will appear as grids of dots.

Contact Sheets

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Relief Printing—Text and Artwork After the Invention of Photography

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Relief Printing—Text and Artwork After the Invention of Photography Two kinds of halftone screens: Older screens consist of two thin glass plates with scribed parallel lines running across them; these are cemented together so the lines form right angles. The thickness of the scribing varies depending on the screen frequency, but the lines and the open spaces are always of equal width. These are now uncommon. Instead, most printers use contact sheets made of film. Unlike glass screens, the dots on these screens are not completely open. Each dot is clear in the middle with increasing opacity toward the edges.

Glass plates

Contact Sheets

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Relief Printing—Platemaking After the invention of photography, relief images could be produced using film positives (or negatives), halftone screens, and photopolymer plates. These plates are made of pre-coated photosensitive plastics, from which unexposed, non-image areas are chemically dissolved.

Light source

Film positive Halftone screen Printed halftone image on coated lightsensitive plate. More intense light burns larger dots.

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Relief Printing—Platemaking the transparency

the halftone screen

Darker areas are recessed. Ink will be applied to the lighter areas, which are raised.

the plate

Keep in mind that the image on this plate is composed of hundreds of thousands of dots. Also note that the plate would not actually look like this. This image only illustrates the difference between the variable sizes of the dots (0100%), which translate into amount of ink applied.

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Relief Printing—The Demise of Letterpress Letterpress has been almost entirely replaced by other printing technologies, especially flexography and lithography (more about these shortly), but it still has a limited “niche” appeal for printing wedding invitations, menus, business cards, etc. It has a very elegant “embossed” look and is very “tactile.”

Lead typesetting (hot type) is mostly an anachronism. This invitation was printed using another kind of relief printing—flexography— which uses photopolymer plates.

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1. 2. 3. 4. 5.

Major Printing Processes: Relief Printing: Flexography

Relief (letterpress and flexography) Planographic (offset-lithography) Gravure (aka, intaglio, rotogravure, photogravure) Screen (aka, stencil, silk screening, screen printing, serigraphy) Digital (aka, electronic)

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Flexography Like letterpress, flexography is a form of relief printing. Flexography uses: • plates of photopolymer or flexible rubber. • thin, fast-drying, water-based inks. • high-speed web presses. Flexography is widely used for printing gift wrap and packaging materials because of its brilliant colors.

Wine bottle labels printed by Richmark Label, Seattle, WA

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Flexography

Flexography is also used for the following: • Corrugated containers • Folding cartons • Paper sacks • Plastic bags • Milk cartons • Disposable cups Other commercial printing by Richmark Label, Seattle, WA

• Labels • Adhesive tapes • Envelopes • Newspapers • Food and candy wrappers

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Flexography

For more information about flexography, visit the following sites: http://desktoppub.about.com/od/flexography/ http://www.pneac.org/printprocesses/flexography/index.cfm

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1. 2. 3. 4. 5.

Major Printing Processes: Planographic (Offset Litho)

Relief (letterpress and flexography) Planographic (offset-lithography) Gravure (aka, intaglio, rotogravure, photogravure) Screen (aka, stencil, silk screening, screen printing, serigraphy) Digital (aka, electronic)

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Planographic (offset lithography) • • • •

By far the most important and versatile printing process today. Developed at the end of the 18th century by Aloys Senefelder. The first chemical printing process. Most newspapers are printed on offset presses.

Five major printing processes: 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Intaglio (gravure) Screen (stencil, silkscreen) Digital

47 Haven’t I seen “litho-” in other words?

The prefix “litho-,” from the Greek lithos, means “stone.” The lithosphere is the solid part of the earth, as distinguished from the hydrosphere and the atmosphere. The “Paleolithic” era is the era of ancient rocks.

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Planographic (offset lithography)

But… Wet limestone repels oilbased ink.

Five major printing processes: 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Intaglio (gravure) Screen (stencil, silkscreen) Digital

An image drawn with a grease pencil repels water and attracts ink.

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Planographic (offset lithography) To print the image on the paper, simply press the paper onto the stone.

Printed image

Sheet of paper

Limestone with inked image + paper

Five major printing processes: 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Intaglio (gravure) Screen (stencil, silkscreen) Digital

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Planographic (offset lithography) Modern litho presses don’t use limestone. They use thin aluminum plates that carry both the image areas and the non-image areas. The image areas are not raised. They are chemically receptive to oil-based inks, whereas the non-image areas are not receptive to the inks. Printed image

The plates, attached to cylinders, are first exposed to water, and then to ink. The image is then transferred to a rubber blanket that is on a second cylinder.

Five major printing processes: 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Intaglio (gravure) Screen (stencil, silkscreen) Digital

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Planographic (offset lithography)

51 This transfer of the image from the printing plate to the “blanket” explains the term “offset.”

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Planographic (offset lithography) Most offset presses are web-fed. These web-fed presses print at speeds up to four times faster than sheet-fed presses—up to 3000 feet per minute, or 100,000 impressions per hour. They are widely used for printing magazines, newspapers,

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Planographic (offset lithography)

A modern offset press, made by Heidelberg

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Dry Offset—A Hybrid Process Dry offset is a hybrid printing technology: • Like other offset printing, it uses a rubber blanket to carry the image from the printing plate to the printing surface. • Like relief printing, however, it has an image area raised above the surface of the plate. • Dry offset is a type of relief rather than planographic printing. http://www.imageinks.ca/support/uvcupinktec1.htm

Dry offset is mostly used for printing on containers.

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Major Printing Processes: Gravure 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Gravure (aka, intaglio, rotogravure, photogravure) Screen (aka, stencil, silk screening, screen printing, serigraphy) Digital (aka, electronic)

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Gravure (aka, intaglio, rotogravure) Recessed image areas are etched into a metal plate to form reservoirs or wells—up to 22,500 per square inch—to receive ink. The size and the depth of the wells control the amount of ink and the density of tone to be transferred to the paper. Five major printing processes: 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Gravure (intaglio) Screen (stencil, silkscreen) Digital

Link: http://www.era.eu.org

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Gravure (aka, intaglio, rotogravure) Two methods 1. Acid etching (traditional) (aka, “chemical gravure”) a) The gravure process starts with a positive photographic transparency of the “copy” (the page or image to be printed). b)Carbon tissue coated with lightsensitive gelatin is placed between the transparency and the printing surface, which may be a copper-coated plate or cylinder. c) The gelatin hardens onto the printing surface according to the amount of light that passes through the transparency. d)The unhardened areas are washed

Positive photographic transparency Halftone screen Carbon tissue coated with light-sensitive gelatin copper-coated plate or cylinder

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Gravure (aka, intaglio, rotogravure) Two methods 2. Electronic etching (aka, “digital gravure”) a) No film or chemicals are involved. b) Digital signals drive engraving heads.

Method 1—acid etching— was developed around 1880 and peaked a century later, when it began to be replaced by method 2, electronic etching. Electronic etching has now replaced most acid etching in Europe and the USA.

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Gravure (aka, intaglio, rotogravure) Advantages: 1. The gravure cylinder has a long service life and will yield a very large number of impressions without degradation. 2. Speed: An 8-unit press can print almost 10 million four-color A-4 pages per hour. Today’s rotogravure presses can run at 15 meters per second, with paper reel widths up to 4.32 meters wide.

Disadvantages:

most expensive of all the processes

Cost of presses and components. a) $1 million for a gravure press vs. $100,000 for a lithographic press. b) $5000 for a single gravure cylinder vs. $15 for a lithographic plate.

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Gravure (aka, intaglio, rotogravure)

A modern high-speed rotogravure printing machine made by Worldly Industrial Co., Ltd.

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Gravure (aka, intaglio, rotogravure) Gravure offers the best image quality of any printing process. It can also maintain this quality over a very long print run. Therefore, gravure is considered ideal for the following types of printing: • Paper currency (banknotes) • Postage stamps • High-end magazines (Vogue) • Mail-order catalogs* • Art books (“coffee-table” books) • Wallpaper and laminates*

*high-volume printing

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Major Printing Processes: Screen Printing 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Gravure (aka, intaglio, rotogravure, photogravure) Screen (aka, stencil, silk screening, screen printing, serigraphy) Digital (aka, electronic)

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Screen Printing The stencil is composed of a screen of silk or other fine mesh. (e.g., nylon, dacron, stainless steel).

Process: • Areas that are not to receive ink are blocked on the screen by application of some impermeable substance: • e.g., adhesive film that has been cut by hand or prepared photographically. • e.g., a brush-on coating • A squeegee is used to press ink through the screen onto the printing surface. • The image is usually built up by using a number of screens with different stencils, each one used to print a

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Screen Printing Advantages:

Disadvantages:

• Suitable for printing on virtually any surface or any shape or size.

• Slow production speeds

• High opacity and brilliance of color. • Inexpensive Uses: apparatus • Fine Art • T-shirts • Logos and lettering on vans

“Marilyn Monroe,” by Andy Warhol

• Reproduction quality not high (but doesn’t need to be…)

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Major Printing Processes: Digital (Electronic) 1. 2. 3. 4. 5.

Relief (letterpress and flexography) Planographic (offset-lithography) Gravure (aka, intaglio, rotogravure, photogravure) Screen (aka, stencil, silk screening, screen printing, serigraphy) Digital (aka, electronic)

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Digital Digital printing, as the name suggests, produces images from digital data. No film is involved in the process. The term “digital printing” covers almost any type of electronic printing, including the following:

Digital printing is both fast and cost-efficient because the following processes, associated with older printing technologies, are eliminated: •Film processing •Stripping*

• Laser (aka, electrostatic, Xerography)

•Platemaking**

• Inkjet

*Stripping: Manual assembly and positioning of the image components.

• Dye-sublimation • Thermal wax transfer • Dot matrix

**Some of the digital printing processes use plates, but there is no “platemaking” component of the process per se.

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Digital Printing • Used mainly in offices and for transactional printing of bills, bank documents, etc., because it can handle variable data very easily. • Ideal for “print on demand” because it does not involve film processing, stripping, or platemaking. • The digital press or printer combines and allocates CMYK (still as halftones) by following the digital encoding in the graphic file. • Uses CMYK inks or toners for color; most digital printers and presses do not print spot colors. (Offers no cost advantage for color monochrome or duotone printing.) *Where the color of a logo is critical (e.g., Coca-Cola), the logo owner may insist on a spot color, in which case digital printing would not be the best option.

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Types of Digital Printing (Reference) Laser (aka, electrostatic, Xerography)

Inkjet

Dye sublimation

Thermal wax transfer

Dot matrix

Process

A laser beam exposes Ink is sprayed dark areas of the final from nozzles image directly onto a directly onto photo-sensitive drum. the printing Those exposed areas material. Each have an electrostatic injet nozzle is charge. The drum is an imaging then dusted with toner unit. particles, which have an opposite charge so that they adhere to the exposed areas. Toner particles are fused to the paper with heat.

A roll of thin plastic A roll of thermal ribbon carries panels of transfer ribbon colored dye. The ribbon contains bands of is sandwiched between colored wax. Nonthe paper and a print impact imaging head containing heads melt dots of thousands of heating CMYK wax. These units. dots are then The heating elements transferred and used to plain or turn the dyes from a solid to a gas, causing specially coated paper. it to sublimate and diffuse, producing single halftone dots.

An “impact” printer. Small wires in the print head transfer ink from a black or multi-colored ribbon onto paper.

Advantages

Low cost, low maintenance Print on plain paper. Resolutions: 300-1200 dpi. Good quality. Useful for “on-

Print is less vulnerable to fading and distortion over time (because the dye infuses the paper). Photo-lab quality. Looks like continuous tone.

Can print multicopy forms because it uses impact. High speeds Low cost

Capable of photo-realistic high-resolution graphics. Can spray ink onto almost any surface.

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Digital Printing—Electrostatic (xerography) • Electrostatic printers use positively-charged toner particles that are attracted to paper which in turn is negatively charged. • The electrostatic process uses a conductive metal (usually aluminum) plate coated with a photoconductive layer of any one of several substances (selenium, silicon, or germanium) that are poor conductors of electricity except when struck by light. When light energy is absorbed (differentially) by their electrons, an electrical current can flow when voltage is applied, and the layer becomes electrostatically charged. • The variation in the amount of charge on the coated metal plate establishes an electrostatic pattern of the image. • The image is rendered visible by application of toner, a powder that carries an opposite charge to that of the plate. • The oppositely charged toner is then transferred to the paper surface and fused there by exposure to solvent vapors or heat. • This process takes about five seconds, and the photoconductive insulating layer can be used many thousands of times before being replaced.

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Spot Colors and Process Colors

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Spot Colors and Process Colors There are thousands of spot colors. They are simply colored inks that are used to produce a printed image without any gradations of hue.

Simulation of a “greyscale” image printed with black ink.

Simulation of the same “greyscale” image printed with green ink (a spot color).

There are only four process colors*: cyan, magenta, yellow, and black (CMYK). They are used to print halftone images with many gradations of hue.

Simulation of 4-color (process) print output

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Spot Colors and Process Colors In the U.S., the major supplier of spot colors is Pantone, which produces the PMS (Pantone Matching System) colors. Other color systems: •Focoltone •Toyo Inks •TruMatch •Munsell

Color swatch books

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Spot Colors and Process Colors Three spot colors are used in this graphic:

1. Black 2. Green 3. Purple

You can create the illusion of more colors by using shades* *ofAlso known spot as “screens,” colors. or “tints.”

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Spot Colors and Process Colors A tint is created by using percentages of full color. 10% is very light, whereas 80% appears more fully saturated*. *In reality, the ink has only one “strength,” but the halftone dots at 10% are smaller than at 90%, allowing more of the background color to appear around them, creating the illusion of a lighter tint.

10%

80%

Variable

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Spot Colors and Process Colors If your job is to be printed by a non-digital process (e.g., offset, flexography, you can select your spot color(s) from a Pantone swatch book. The colors are printed on both coated and uncoated paper, because your job will be printed on one or the other of these. So make sure you’ve chosen the right one. Here, the “U” after the PMS number indicates “uncoated.”

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Spot Colors and Process Colors Although you can initially choose your color from the monitor (using software that features it), this is not advisable because of gamut* issues. After you have chosen your color from the swatch book, then select the same color from your software PMS color list. You will use this color while you are working on your project. *Gamut: The range of colors that a device or a medium can display. The printer’s gamut will always be more restricted

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Spot Colors and Process Colors When you print a “proof” to your own printer: You will at some point want to print a “proof”* of your job to your own printer. Once again, remember that the printer is not using spot colors but CMYK, so don’t expect your “proof” to look like the final printed version, which will have been done with spot colors. Inkjet Final proof print

* I.e., from your personal or office printer. This is not the same as the proof (“matchprint” or “pressmatch”) that the press will send you for approval.

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Spot Colors and Process Colors If you want to show a customer a proof from your own printer, a laser printer rather than an inkjet one is recommended. Also, you may use a different kind of Pantone swatch book, called a color specifier, which lets you tear out chips of the PMS colors and place them on your color proof for the customer to see. Inkjet proof

Final print

Module 2: Printing Processes

Spot Colors and Process Colors Process colors In the 4/c process, four colors are mixed together in various percentages to create thousands of colors. When you send your service bureau a Photoshop file using CMYK mode, the service bureau can separate out the color channels to create the “positives”, which might look like the four lower ones shown here. Note The film positives shown here are colored for explanatory purposes only. As their only purpose is to let light through differentially, they would all look more or less

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Spot Colors and Process Colors If a part of your graphic is monochrome, you may want to use the Pantone swatches to identify the desired color even if that color is going to be produced as a process color. The swatches will give you the CMYK values, which you can then key in to the fields next to the color sliders in Photoshop.

All printed in CMYK, but the color for the lower section is selected from a color library. (The CMYK values are keyed in.) (This section in a single color)

The other option for the lower section is to print it using a spot color—a good choice if there is a company

Module 2: Printing Processes

Spot Colors and Process Colors If your graphic uses three or more spot colors, it’s probably more cost-effective to have the printing done in 4/c process.

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Metallic Colors • Metallics add expense to the job because they cannot be reproduced using process colors. They are run as an additional spot color. • Four-color jobs are usually run on four-color presses, where there’s a station for each color. • If you want metallics, you’ll need to find a press that has the extra stations, or the job will need to be run through a second time. You can work with your printer about this.

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Varnishes Varnishes can be applied to the finished piece, but, again, they require an additional station on the press. The main purpose of a varnish is to intensify the colors and to protect the print.

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Continuous Tone vs. Halftone

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Continuous Tone (aka “contone”) and Halftone Contone image

Halftone image

You’ll see continuous tone images in...

You’ll see halftone images in...

•Photographic prints (no dots)

Printed material (dots)

•Computer monitor images (composed of pixels)

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Continuous Tone (aka “contone”) and Halftone Contone image

Halftone image

Contone dots… • are varying saturations of the same color (here, black) • have uniform spacing. • have uniform size.

Halftone dots… • are all one color (here, black). • have uniform spacing. • vary in size. Halftone dots create an optical illusion of continuous tone.

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Continuous Tone (aka “contone”) and Halftone Contone image

Halftone image

Mass printing technologies cannot produce genuine continuous tone. You see continuous tone on your computer monitor. Photographic prints are also continuous tone, but without the dots (and they are not a mass printing

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Continuous Tone (aka “contone”) and Halftone Yes, a computer monitor produces continuous tones. Remember, it is an analog device. While it is true that the monitor projects thousands of tiny spots of light onto a phosphor screen, the spots are all the same size, and each one is capable of displaying colors in their full ranges of hue, saturation, and brightness. Print technology cannot do this. It can only place dots of ink in varying sizes on a surface (usually paper). Color hue, saturation, and brightness are achieved by layering four colors of ink (CMYK) in various proportions and at various angles. This is

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Continuous Tone (aka “contone”) and Halftone The difference between digital and non-digital printing technologies is in the way the ink gets to the paper. Whereas digital processes can send an image directly from the computer to an plate or drum, the major non-digital printing processses uses film to produce plates. They accomplishes this through the use of halftone screens—one for each color of ink that is used.

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Halftone Screens, Halftone Images Clarifications: 1. When we refer to “halftone screens,” we may be referring to one of two things: • The actual screens through which light passes to the light-sensitive surface of the printing plate. • The image that is produced by this process. 1. Although both digital and non-digital printing work by placing dots of ink on a surface, only non-digital (mainly offset) printing uses halftone screens.

Terminology:

It is preferable to use “halftone image” for the second one of these, but you will sometimes hear it referred to as a “halftone screen.”

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Printing Halftone Images

10%

20%

30%

40%

50%

In this example, the dots representing gray shades up to 50% will appear as black spots on white.

60%

70%

80%

90%

100%

Those representing shades of gray over 50% will appear as white dots on black.

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Printing Halftone Images (offset process)

10%

20% 30%

40% 50%

Note: What you’ve just seen can apply to any of the four CMYK inks. A full-color (4/c) printed image requires one plate for each of the inks.

60%

70% 80%

90% 100%

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Printing Halftone Images (offset process)

Halftone resolution: • Measured in lines per inch (lpi) • Varies according to the number of lines in the (physical) halftone screen

Screen rulings (lpi) range from 30 to 300 lpi.

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Printing Halftone Images (offset process) low screen frequency

33 lpi

high screen frequency

53 lpi

Line screen frequency, measured in lines per inch (lpi), describes the granularity of the halftone screen.

75 lpi Some paper, such as newsprint (used for newspapers), is too absorbent for the higher line screen frequencies. Higher line screens require better quality papers.

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Printing Halftone Images (offset process) Screen Angle In addition to screen frequency, the printer must take into account the angle of the screen. The illusion of continuous tone in a printed image is best when the screen is angled at 45°.

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Printing Halftone Images (offset process) All the images below are at 75 lpi, but the pattern of the screen is highly visible when angled at 0° and 20°. A screen set at a 45degree angle produces an image closer to continuous tone. 45° is the preferred screen angle for all grayscale halftones and is always used for black in 4/c process printing.

0 degrees

20 degrees

45 degrees

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Printing Halftone Images (offset process) Dot gain

Dot gain may result from the following: •Overexposure during platemaking •Transferring too much ink from the plate to the blanket •Using lower-quality paper, which is more porous

An example of dot gain

The greatest dot gain results from using lower-quality paper.

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Printing Halftone Images (offset process) Compensating for dot gain: a pre-press operation

To compensate for dot gain, do the following: 1.Find out from your printer what the percentage of dot gain is expected to be, given the paper quality, the inks, etc. 2.In your imaging software (e.g., Photoshop), find the setting for dot gain and enter that percentage there.

Module 2: Printing Processes

End of Module 1 Online resources: •A Technical Dictionary of Printmaking, by André Béguin: http://www.polymetaal.nl/beguin/alfabet.htm

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