16 page publication
DESCRIPTION
What is design for print?TRANSCRIPT
Colour & Print
About
This book will act as a reference guide for understanding the print process.
It will cover the basics of colour theory without getting too ‘sciency.’ It will identify a few verieties of image treatment and colour manipulation that
can be useful for print prodution.
It will also provide you with some hints and tips when preparing a document for print. As well as explaining industrial level printing methods and a brief explanation of the variety of stocks
available.
Index of content
About
Index
Index
RGB
Additive colour
CMYK
Subtractive colour
Greyscale
Halftone
Monotone
Duotone
Overprinting
1.2.3.4.
.5
.6
.7
.8
...continued
Tints
Preparing for print
Rotogravure
Offset lithography
Flexography
Screen printing
Spot varnishing
Foil blocking
Embossing
Stock
Bibliography
9.10.11.12.
.13
.14
.15
.16
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RGB
The additive colour model is used to describe colour that exists in light form and is emitted from a source such as a
TV screen, a computer or a flame. It is based on the primary hues of red, green and blue (RGB), which are the primary
hues of light.
When two additive hues overlap a subtractive primary is produced. The complimentary hues are cyan, magenta
and yellow. In this case the mixture of the three of equal intensity form to make white, while the absence of all three
produces black.
The additive system works through direct projected light that is visible from the source. It is important to note that colour created from light is unable to present colours with
the same intensity as colour created from pigment.
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CMYK
The subtractive colour model is used to describe colour that exists in pigment form and is applied to physical surfaces,
such as ink on paper. It is based on the primary hues of cyan, magenta and yellow (CMY), with black (K).
When two subtractive colours overlap an additive primary is produced. The complementary hues are red, blue and green. In the subtractive model and mix of the three primary hues,
of equal intensity, will form black and subtract toward white.
The subtractive system works through the reflection and absorption of light. This is how the human eye perceives
colour.
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Greyscale / Halftone
Image saturated of all colour. Can then be used
as a monotone or duotone image.
Greyscale
Image is made up of black and white dots, indicating
shade and depth. Made popular by pop art.
Halftone
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Monotone / Duotone
Using a single colour to produce different shades and saves on production
costs.
Monotone
Uses two colours. Creates tints and also can reduce
production costs.
Duotone
8
Over-printing
When you print opaque colours, the
colour on the top ‘knock out’ the area
below it. However you can use over
printing to prevent knockout and make
the uppermost printing ink transparent,
in relation to the in underneath.
Ink, stock and printing method will
all result in different degrees of
transparency. So if you are unsure
consult your printer to determine how it
will turn out.
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Tints & Spot
Tinting colours is similar to
overprinting. The difference is you
merge two or more colours together to
create a new ‘tint’ of the same ink.
Reductions can also be used on single
colour prints to make it seem as though
more colours have been used. For
example you may have a spot colour
which is at 100%. You can then reduce
the colour by specific percentages which
changes the tonal value. However going
below 10% would be nearing the point
where the human eye no longer can
distinguish between white and the tint.
The benefit of limiting your colour
pallet is that it saves on production
costs as less ink is being used.
“
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Preparing for print
Swatches & colour checking
Colour checking is very important before printing. First you want to make sure your document is in the right colour format (CMYK or RGB). Then to save any confusions or mistakes delete all the colour swatches not being used from the swatches tab.
This is exemplified on the right.
When sending a job off to the printer keep all images and word documents together in one file.“
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Rotogravure / Offeset Lithography
Rotogravure presses can produce a vast range of print jobs. They can be as narrow as labels used on envelopes or shipping packages, or as wide as 12 feet wide rolls of vinyl. The rotogravure press is not restricted to just paper or foil. In fact, materials such as plastic or foil can be printed on through several processes that include electrostatic pull and applied pressure. A rotogravure press includes an ink fountain engraved cylinder, a doctor blade, a dryer, and an impression roller. The engraved ink fountain cylinder is versatile enough to be changed to meet the requirements of each job layout. Generally, these changes are made by adjusting its circumference. A printing job on a rotogravure commences when the cylinder is dipped into the ink. As it is immersed, the cells of the cylinder become filled with ink. Each rotational movement of the engraved cylinder causes it to become filled with more ink. Next, the material to be printed on is placed between the engraved cylinder and the impression roller. In this way, the ink from the cell is transferred to the material. The final process is for the material and the newly applied ink to pass through a drying method. The drying process prepares the material to receive another color of ink. Each color on a rotogravure press has its own printing unit.
The first step in offset lithography is making a plate with the image to be printed. If the image is in black and white, only a single plate is required, because the plate can be inked with black ink. Color images are produced using a four-color separation process, in which four different plates are made for the cyan, magenta, yellow, and key (black) inks; when the plates are printed, the colors blend together visually, creating a color image. Plates in offset lithography are entirely flat, in contrast with the textured surfaces of engraved plates. They are made by creating a film negative of the image, placing it over a photo-sensitive plate, exposing it, and then developing it. Once the plate is made, it can be mounted in a press. This technique takes advantage of the fact that oil and water do not mix. The plate is brushed with rollers coated in water, and then with rollers covered in ink. The ink attracts to the parts of the plate which were exposed earlier, while the water keeps the unexposed portions clear so that they do not smear or transfer ink. Then, the plate transfers the ink to a rubber roller known as a “blanket,” and the blanket rolls across the paper; typically the paper is fed between the blanket and another roller to ensure that the image stays crisp. An offset press can run continuously, which makes it extremely fast. Depending on the job, the press may be sheet fed, or web-fed, in which case the paper is on huge rollers. In both cases, the paper is typically run through an oven after printing so that it dries quickly, preventing smears, and then it can be cut, bound, folded, and prepared for distribution.
Flexography printing uses a printing plate made of rubber or plastic.
Ink is applied to a raised image on the plate, this transfers the image
onto the substrate. The ink used is ideal for printing onto materials
such as plastics and foils. Therefore it is the predominant method
used for printing a wide veriety of packaging such as flexible bags and
wrappers. They are also useed for prointing onto thick compressible
materials sich as cardboard.
All images, text and illustrations are photo-
copied to convert them into the proper posi-
tive or negative films to make the printing
plate which then reproduces the image on
the substrate.
Flexographic printing has considerable
impact on the environment
based on the use of rubber
and photopolymer plates,
solvent-based inks, and hy-
drocarbon solvents, as well
as a broad range of sub-strates. Printers
select and mix
chemicals for a
variety of pre-
press and press-
room applica-
tions. Darkroom
chemistry,
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Flexography
platemak-
ing, inks and
solvents, and maintenance all use
chemicals to achieve
the ultimate goal of
transferring a quality im-
age to a substrate
(Shapiro, 1993a).
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Screen printing / Spot varnishing
What you will need to print
Water resistant tapeNews paper print
SpongeAccess to water
photosensitive emulsionUV light box or strong lamp
Stripping chemicalsHeated cupboard or powerful hair dryer
AcetatePrinter
SqueegeeInk
Step by step
Acquire a paper or a textile screen depend-ing on your substrate. Coat the surface of the screen with photo-sensitive emulsion in a dark room.Dry the emulsion in heated room or with hair dryer.Print out your design onto acetate.Position acetate on screen and expose to a bring light source.Wash down the screen with sponge to re-veal your design.Dry off screen again.Place screen on substrateUse squeegee to spread ink evenly over screen.
Foil blocking / Embossing
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f oil blocking also involves a screen. However instead of printing ink you are printing glue. Once the glue is dried spread a sheet of foil over it and heat it in a press at 150 degrees for 12-14 seconds.
mbossing can be acieved at varied degrees
of quality. Either by using a stencil or an
etching plate.
To achieve the best results and etching plate
should be used.
The image is exposed using photographic
film under a UV exposing machine leaving a
coated layer on the negative of your design.
It is then placed into a vat of chemicals
which eats away at the exposed area (your
design) of copper.
After six hours approxemately 2mm will
have been eroded, enough for you to emboss
with.
All that is then left to do it apply 5000psi to
the copper sheet with your substrate under-
neath it.
E
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Stock
Experimenting with substrates can be very reward-
ing. They can greatly enhance the look of your
work without having to make any major design
decisions.
There are two basic types of paper that can be used
for print; uncoated & coated. The uncoated stocks
are usually matt or even textured. Textured papers
will cost more than smooth because they have more
material and therefore a greater gsm. Coated pa-
pers vary in degrees of glossiness, and usually can
produce a higher quality print finish.
The term gsm stands for ‘grams per sq. meter’ and
indicates the weight and thickness of the stock. It
can vary from very low gsm, 30 gsm for example
which is about the thickness of tissue paper, to
nearly 400 gsm by which point it is more like board.
Before printing you must make sure the printing
method chosen is compatible with your chosen
stock.
Metric Name
A5
A4
A3
A3+
A2
A1
A0
Metric Size
148 x 210 mm
210 x 297 mm
297 x 420 mm
329 x 483 mm
420 x 594 mm
594 x 841 mm
841 x 1189 mm
U.S. Equivalent
5.8 x 8.3 inches
8.3 x 11.7 inches
11.7 x 16.5 inches
13 x 19 inches
16.5 x 23.4 inches
23.4 x 33.1 inches
33.1 x 46.8 inches
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