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
1. 2. 3. 4.
About
.5 .6 .7 .8
CMYK Subtractive colour
Index
Greyscale Halftone
Index
Monotone Duotone RGB Additive colour
Overprinting
...continued
9. 10. 11. 12.
Tints
Preparing for print
Foil blocking Embossing
Rotogravure Offset lithography
Flexography
.13 .14 .15 .16
Screen printing Spot varnishing
Stock
Bibliography
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
Greyscale
Image saturated of all colour. Can then be used as a monotone or duotone image.
Halftone
Image is made up of black and white dots, indicating shade and depth. Made popular by pop art.
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Monotone / Duotone
Monotone
Using a single colour to produce different shades and saves on production costs.
Duotone
Uses two colours. Creates tints and also can reduce production costs.
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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.
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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.
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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 fourcolor 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
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 photocopied to convert them into the proper positive 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 hydrocarbon solvents, as well as a broad range of substrates. Printers select and mix chemicals for a variety of prepress and pressroom applications. Darkroom chemistry, platemaking, inks and solvents, and maintenance all use chemicals to achieve the ultimate goal of transferring a quality image to a substrate (Shapiro, 1993a).
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Screen printing / Spot varnishing
What you will need to print Step by step Water resistant tape News paper print Sponge Access to water photosensitive emulsion UV light box or strong lamp Stripping chemicals Heated cupboard or powerful hair dryer Acetate Printer Squeegee Ink
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Acquire a paper or a textile screen depending on your substrate. Coat the surface of the screen with photosensitive 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 reveal your design. Dry off screen again. Place screen on substrate Use squeegee to spread ink evenly over screen.
Foil blocking / Embossing
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.
E
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 underneath it.
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Stock
Experimenting with substrates can be very rewarding. 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 papers 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.
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Metric Name
Metric Size
U.S. Equivalent
A5
148 x 210 mm
5.8 x 8.3 inches
A4
210 x 297 mm
8.3 x 11.7 inches
A3
297 x 420 mm
11.7 x 16.5 inches
A3+
329 x 483 mm
13 x 19 inches
A2
420 x 594 mm
16.5 x 23.4 inches
A1
594 x 841 mm
23.4 x 33.1 inches
A0
841 x 1189 mm
33.1 x 46.8 inches
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Edward N Webb 07870373856 e-webb0811.blogspot.com ed_webb_@hotmail.co.uk