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Module 2: Printing Processes 1 Module 2: Printing Processes Instructor: Doughlas Remy

Module 2: Printing Processes

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Module 2: Printing Processes. Instructor : Doughlas Remy. Topics Covered in This Module. The U.S. printing industry Definition of printing Major printing processes (overview) Where’s the ink? Where’s the paper? Early relief printing - PowerPoint PPT Presentation

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Module 2: Printing Processes 1

Module 2:Printing Processes

Instructor: Doughlas Remy

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Topics Covered in This Module

• 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• Relief (Flexography, Letterpress)• Planographic printing (offset litho)• Gravure (Intaglio)• Screen printing (silkscreen, stencil)• Digital (electronic) printing• Spot colors and process colors• Continuous tone vs. halftoneQuizAnswer Forms for Printing

(major printing processes)

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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).

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)

Sources Targets

PaperFabricMetalPlastic

Media

InksTonersDyesPaints

most common

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Major Printing Processes

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• Relief (primarily flexography, which evolved from letterpress)

• Planographic (offset lithography)

• Gravure (aka Intaglio, Photogravure, Rotogravure)

• Screen (aka silkscreen, stencil, serigraphy)

• Digital (aka electronic)

Major Printing Processes

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Major Printing Processes

In a category by itself because1. it is for low-volume printing; and2. its technology is so different from

the others.

• 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

Now a major printing process and growing exponentially. Its technology is very different from that of the first three on this list.

• 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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• Relief (primarily flexography, which evolved from letterpress)

• Planographic (offset lithography)

• Gravure (aka Intaglio, Photogravure, Rotogravure)

• Screen (aka silkscreen, stencil, serigraphy)

• Digital

Major Printing Processes

We will focus on the first three for now.

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• Relief (primarily flexography, which evolved from letterpress)

• Planographic (offset lithography)

• Gravure (aka Intaglio, Photogravure, Rotogravure)

Major Printing Processes

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Major Printing Processes:

Where’s the ink?Where’s the paper?

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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:

Where’s the ink?

Relief Ink is on a raised surface.

Planographic Ink is on a flat surface.

Gravure 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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1. The paper may be attached to a flat surface, against which a type form or a printing plate is pressed.

Where’s the paper? (1)

lever attached to screw

Note This way of placing the paper was a feature of the earliest printing methods and is rarely used today. (It’s very slow.)

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

type form

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Lever Press

This was a later development, using the same principle of attaching the paper to a flat surface.

Where’s the paper? (1)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.

Paper attached here.Note that there is no

screw.

The “chase” (relief image)

Message from Ed Evetts at CCS Printing in Bellevue:..the disc is where the operator places the ink for the press. The ink-carrier roller-arm (not apparent in the illustration) rotates up and rolls across the flat part of the disc, picking up a layer of ink on the roller. Then, on the down-stroke, the ink-carrier roller-arm rotates down and applies a layer of ink to the raised-surface of the copy in the chase.which Doughlas refers to as the "Type form" in the illustration.  FYI: As the ink-carrier roller-arm rotates up to get more ink, the sheet attached to the paper-bed rotates to contact the chase and get "printed". When the ink-carrier roller-arm rotates down to apply more ink to the chase, the paper-bed rotates away from the chase so that the operator can pull off the printed sheet and insert a fresh sheet for printing .

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2. The paper may be attached to a cylinder, which then rotates as an inked type form passes beneath it.

Where’s the paper? (2)

Paper

Impression Cylinder

InkRollers

Press bed

Typeform

Cylinder Letterpress

Note This way of placing the paper, like the previous one, was time-consuming and was abandoned in favor of the last two methods (next slides).

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3. Sheets of paper pass between two flexible printing plates (attached to cylinders) that are carrying the image.

Where’s the paper? (3)

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

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.

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

Where’s the paper? (4)

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Where’s the paper? (4)

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.

Why “Web”?

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• Relief (primarily flexography, which evolved from letterpress)

• Planographic (offset lithography)

• Gravure (aka Intaglio, Photogravure, Rotogravure)

• Screen (aka silkscreen, stencil, serigraphy)

• Digital

Major Printing Processes

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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.

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

Modern signet rings a wax seal

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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

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.“Old Reliable,” platen letterpress, 19th

century.

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

Paper

Relief: Letterpress—Later Developments

Impression Cylinder

InkRollers

Press bed

Typeform

Cylinder Letterpress

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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A cylinder letterpress

Relief: Letterpress

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Major Printing Processes:

Relief Printing: Text and Artwork Before and After the

Invention of Photography

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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: The Soldier and his Wife, by Daniel Hopfer (ca 1470-1536)

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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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 transparencies, we must first understand what a halftone screen is.

Relief Printing—Text and Artwork After the Invention of Photography

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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.

• 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.

Relief Printing—Text and Artwork After the Invention of Photography

Glass plates

Contact Sheets

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Relief Printing—Text and Artwork After the Invention of Photography

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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

Two kinds of halftone screens:

Relief Printing—Text and Artwork After the Invention of Photography

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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.

Halftone screen

Film positive

Printed halftone image on coated light-sensitive plate. More intense light burns larger dots.

Light source

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Relief Printing—Platemaking

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

the transparency

the halftone screen

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 (0-100%), 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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Major Printing Processes:

Relief Printing: Flexography

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Gravure (aka, intaglio, rotogravure, photogravure)4. Screen (aka, stencil, silk screening, screen printing, serigraphy)5. Digital (aka, electronic)

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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.

Flexography

Wine bottle labels printed by Richmark Label, Seattle, WA

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Flexography is also used for the following:

• Corrugated containers

• Folding cartons• Paper sacks• Plastic bags• Milk cartons• Disposable cups• Labels• Adhesive tapes• Envelopes• Newspapers• Food and candy

wrappers

Flexography

44

Other commercial printing by Richmark Label, Seattle, WA

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For more information about flexography, visit the following sites:

http://desktoppub.about.com/od/flexography/

http://www.pneac.org/printprocesses/flexography/index.cfm

Flexography

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Major Printing Processes:

Planographic (Offset Litho)

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Gravure (aka, intaglio, rotogravure, photogravure)4. Screen (aka, stencil, silk screening, screen printing, serigraphy)5. Digital (aka, electronic)

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• 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.

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.

Five major printing processes:

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Intaglio (gravure)4. Screen (stencil, silkscreen)5. Digital

Planographic (offset lithography)

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Planographic (offset lithography)

Five major printing processes:

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Intaglio (gravure)4. Screen (stencil, silkscreen)5. Digital

But…

Wet limestone repels oil-based ink.

An image drawn with a grease pencil repels water

and attracts ink.

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Planographic (offset lithography)

Five major printing processes:

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Intaglio (gravure)4. Screen (stencil, silkscreen)5. Digital

Sheet of paper

Limestone with inked image + paper

Printed image

To print the image on the paper, simply press the paper onto the stone.

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Planographic (offset lithography)

Five major printing processes:

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Intaglio (gravure)4. Screen (stencil, silkscreen)5. Digital

Printed image

Modern litho presses don’t use limestone.

They use thin aluminum plates that carry both the image areas and the non-image areas. (Polyester plates are used for some jobs that involve line copy or that require short runs only.)

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.

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.

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Planographic (offset lithography)This transfer of the image from the printing plate to the “blanket” explains the term “offset.”

* Inks are now soy-based, not oil-based.

*

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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, catalogs, and books.

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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. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Gravure (aka, intaglio, rotogravure, photogravure)4. Screen (aka, stencil, silk screening, screen printing, serigraphy)5. 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.

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

Five major printing processes:

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Gravure (intaglio)4. Screen (stencil, silkscreen)5. Digital

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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). The halftone screen is placed under the transparency.

b) Carbon tissue coated with light-sensitive gelatin is placed between the halftone screen 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. (More light = more hardened gelatin)

d) The unhardened areas are washed away and etched with acid.

Positive photographic transparency

Carbon tissue coated with light-sensitive gelatin

Gravure (aka, intaglio, rotogravure)

copper-coated plate or cylinder

Halftone screen

The inked areas correspond to the areas where the gelatin was not hardened by the greater amount of light passing through the transparency.

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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.

Gravure (aka, intaglio, rotogravure)

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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:

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.

Gravure (aka, intaglio, rotogravure)most expensive of all the processes

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

Gravure (aka, intaglio, rotogravure)

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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 idealfor 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*

Gravure (aka, intaglio, rotogravure)

*high-volume printing

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Major Printing Processes:

Screen Printing

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Gravure (aka, intaglio, rotogravure, photogravure)4. Screen (aka, stencil, silk screening, screen printing, serigraphy)5. Digital (aka, electronic)

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Screen Printing

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 separate color.

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

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Disadvantages:

• Slow production speeds

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

Uses:• Fine Art• T-shirts• Logos and lettering

on vans“Marilyn Monroe,” by

Andy Warhol

Advantages:

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

• High opacity and brilliance of color.

• Inexpensive apparatus

Screen Printing

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Major Printing Processes:

Digital (Electronic)

1. Relief (letterpress and flexography)2. Planographic (offset-lithography)3. Gravure (aka, intaglio, rotogravure, photogravure)4. Screen (aka, stencil, silk screening, screen printing, serigraphy)5. 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:

• Laser (aka, electrostatic, Xerography)

• Inkjet

• Dye-sublimation

• Thermal wax transfer

• Dot matrix

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

• Film processing

• Stripping*

• Platemaking**

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

**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 and images very easily. Can work off database data.

• The large digital printers used in printing companies are simply larger versions of the inkjet printers used in offices. E.g., the Hewlett-Packard indigo. Prints up to 1000 copies at 2000 sheets/hr. After that it is more cost-effective to go to offset, which prints up to 11,000 sheets/hr.

• 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 dark areas of the final image directly onto a photo-sensitive drum. Those exposed areas have an electrostatic charge. The drum is then dusted with toner particles, which have an opposite charge so that they adhere to the exposed areas. Toner particles are fused to the paper with heat.

Ink is sprayed from nozzles directly onto the printing material. Each injet nozzle is an imaging unit.

A roll of thin plastic ribbon carries panels of colored dye. The ribbon is sandwiched between the paper and a print head containing thousands of heating units.The heating elements turn the dyes from a solid to a gas, causing it to sublimate and diffuse, producing single halftone dots.

A roll of thermal transfer ribbon contains bands of colored wax. Non-impact imaging heads melt dots of CMYK wax. These dots are then transferred and used to plain or specially coated paper.

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

Advantages Low cost, low maintenancePrint on plain paper.Resolutions: 300-1200 dpi.Good quality.Useful for “on-demand”

printing.Faster than inkjet

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

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 multi-copy forms because it uses impact.High speedsLow cost

Disadvantages More expensive than inkjetNot suitable for long runs.

Still pricy for home offices. Low resolution

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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.

For Reference

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Exercises:

Process

a) Letterpressb) Offset lithoc) Gravured) Silkscreene) Digital

A. Match each of the following printing jobs to a suitable process.

1. A mail-order catalog that will be distributed to about 20 million customers nationwide

2. A newspaper

3. 3000 milk cartons

4. Bank statements sent to individual customers

5. 100 copies of a company report

6. A company logo for printing on the doors of a utility vehicle

7. A “coffee-table” art book containing high-quality photos of artwork by French Impressionist painters

8. Labels for jam jars

9. The glossy cover for a retail catalog that will be sent to thousands of customers. The customers’ mailing addresses will be printed on the cover.

10.An image on a t-shirt.

11. A postage stamp

12.A college catalog

13.An embossed invitation

____

____

____

____

____

____

____

____

____

____

____

____

____

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Exercises:

Process

a) letterpressb) planographic

printingc) gravured) xerographye) stencilf) relief printingg) web offseth) digital printing

B. Complete each sentence with a term from the list on the right.

1. “Intaglio” is another name for ____.

2. Offset lithography is an example of ____.

3. The oldest printing process is ____.

4. Dot matrix is a kind of ____.

5. Your worst choice for printing company logos where precise color is critical is ____.

6. The signet ring was used as a early means of ____.

7. ____ has a very elegant “embossed” look and is used for printing wedding invitations and menus.

8. ____ uses tiny wells to hold the ink.

9. ____ is the slowest printing process.

10.____ uses a rubber blanket to transfer the image to the paper.

11. ____ uses etching to make the printing plates.

12.____ is the most expensive printing process.

13.____ is another name for laser printing

14.____ uses the simplest apparatus.

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Spot Colors and Process Colors

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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

Spot Colors and Process Colors

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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

Spot Colors and Process Colors

Color swatch books

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Three spot colors are used in this graphic:

1. Black

2. Green

3. Purple

Spot Colors and Process Colors

You can create the illusion of more colors by using shades* of spot colors.

* Also known as “screens,” or “tints.”

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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.

Spot Colors and Process Colors

10% 80% Variable

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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.”

Spot Colors and Process Colors

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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.

Spot Colors and Process Colors

*Gamut: The range of colors that a device or a medium can display. The printer’s gamut will always be more restricted than a monitor’s.

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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.

* 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.

Inkjet proof

Final print

Spot Colors and Process Colors

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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

Spot Colors and Process Colors

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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 like the one in the lower right corner.

Spot Colors and Process Colors

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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.

Note: The top portion of this ad would have to be printed in 4/c.

(This section in a single color)

Spot Colors and Process Colors

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

The other option for the lower section is to print it using a spot color—a good choice if there is a company logo (exact color critical).

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

Spot Colors and Process Colors

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• 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.

Metallic Colors

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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.

Varnishes

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Continuous Tone vs. Halftone

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You’ll see continuous tone images in...

• Photographic prints (no dots)

• Computer monitor images (composed of pixels)

Halftone imageContone image

Continuous Tone (aka “contone”)and Halftone

You’ll see halftone images in...

Printed material (dots)

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Halftone dots…• are all one color

(here, black).• have uniform

spacing.• vary in size.

Halftone imageContone image

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

Halftone dots create an optical illusion of continuous tone.

Continuous Tone (aka “contone”)and Halftone

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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 technology).

Halftone imageContone image

Continuous Tone (aka “contone”)and Halftone

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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 true of both digital and non-digital printing technologies.

Continuous Tone (aka “contone”)and Halftone

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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.

Continuous Tone (aka “contone”)and Halftone

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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.

2. 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.”

Halftone Screens, Halftone Images

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10% 50%20% 30% 40%

60% 100%70% 80% 90%

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

Printing Halftone Images

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10% 50%20% 30% 40%

60% 100%70% 80% 90%

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.

Printing Halftone Images (offset process)

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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.

Printing Halftone Images (offset process)

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33 lpi 53 lpi 75 lpi

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

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

low screen frequency high screen frequency

Printing Halftone Images (offset process)

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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°.

Printing Halftone Images (offset process)

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0 degrees 20 degrees 45 degrees

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 45-degree 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.

Printing Halftone Images (offset process)

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An example of 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

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

Dot gain

Printing Halftone Images (offset process)

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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.

Compensating for dot gain: a pre-press operation

Printing Halftone Images (offset process)

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Module 2 Quiz (1)

Continued...

Instructions: Mark your answer on the distributed answer sheet. More than one answer may be correct.

1. Vellum is made from...a. leaves.b. cotton fiber.c. animal tissue.d. wood fiber.

2. Platen letterpress does not use...a. a cylinder.b. metal type.c. a type form.d. web-fed paper.

3. When it was first invented, lithography used...a. magnetic toner.b. metal type.c. wet limestone.d. a duplexing unit.e. rubber rollers.

4. The term “offset” is used because...a. the printing plate does not contact the paper.b. the guide rollers are set off from the cylinders.c. water wets the plate before ink is applied.

5. Nowadays, gravure plates are etched with...a. acid.b. engraving heads.c. knives.d. laser beams.

6. A press that allows printing on both sides of the paper is said to have ___ capability.

a. offsetb. electrostaticc. re-imagingd. duplexing

7. Before the invention of photography, artwork could only be printed by using...

a. contact sheets.b. glass plates.c. halftone screens.d. engravings or etchings.

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Module 2 Quiz (2)

Continued...

8. The transparent dots on a halftone contact sheet are...

a. different sizes.b. all the same size.

9. The inked dots on a printed photograph (e.g., in a newspaper) are...

a. different sizes.b. all the same size.

10. To create a halftone image, you must start with...a. a platen.b. a rubber cylinder.c. a film negative or positive.d. a silk screen.

11. Pantone is a supplier of...a. spot colors.b. process colors.c. Munsell colors.d. Acrylic paints.

12. Why must you exercise caution when selecting spot colors from a computer program?

a. Not all colors are shown.b. They are proprietary.c. They are not as luminous.d. Monitor and printer gamuts are different.

13. A “matchprint” is a kind of proof that is produced by the...a. pre-press person.b. press.c. customer.d. page layout software.

14. If you want to show a customer the exact spot color that will be used in a job, you should show the customer...

a. an inkjet proof.b. a color laser proof.c. a color swatch.d. a screen shot from Photoshop.

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Module 2 Quiz (3)

15. Spot colors might be appropriate when the printed material is to have …

a. fewer than four colors b. metallic colors c. more than four colors d. more than eight colors

16. When magnified, gray shades up

to 50% appear as… a. black dots on white. b. white dots on black. c. black lines on white. d. white lines on black.

17. A low screen frequency might be

appropriate for printing … a. banknotes b. newspapers c. textbooks d. wine bottle labels

18. The best screen angle for a printed grayscale image is generally considered to be ___ degrees.

a. 90 b. 45 c. 20 d. 30

19. Dot gain may result from…

a. too much ink b. low quality paper c. overexposure during

platemaking

20. Compensating for dot gain is a(n) ____ operation.

a. pre-press b. on-press c. post-press

21. Digital printers and presses do not use…

a. dots b. film c. plates d. photographic

transparencies

22. Where would you find continuous tone images?

a. photographic prints b. computer monitor images c. printed material

23. Continuous-tone (contone) dots

… a. vary in size. b. have uniform spacing c. have uniform size.

(End of quiz)

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

End of Module 2

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Module 2: Printing Processes 105Answer forms

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e12. a b c d e13. a b c d e 14. a b c d e15. a b c d e16. a b c d e 17. a b c d e18. a b c d e19. a b c d e 20. a b c d e21. a b c d e22. a b c d e 23. a b c d e

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e12. a b c d e13. a b c d e 14. a b c d e

Module 1:Introduction

Module 2: Printing Processes Module 3:Color Theory and Mgmt

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e12. a b c d e

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e

Section 1

Section 2

24. a b c d e 25. a b c d e 26. a b c d e 27. a b c d e 28. a b c d e 29. a b c d e 30. a b c d e 31. a b c d e 32. a b c d e 33. a b c d e34. a b c d e35. a b c d e36. a b c d e 37. a b c d e38. a b c d e39. a b c d e 40. a b c d e41. a b c d e42. a b c d e 43. a b c d e44. a b c d e45. a b c d e 46. a b c d e

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Module 4: Tools and Techniques

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e

Section 1

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e

Section 2

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e

Section 3

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e

Section 4