Printing methods – what you need to know 1.Colour separation 2.Process colours 3.CMYK 4.Registration marks and the order of application of colours 5.Digital printing

DEFINITIONS COLOUR BARS – bars of colour around a printed image to check the density of the colours being printed CROP MARKS – marks incorporated in a printed sheet to indicate where the paper is to be trimmed or cut to size DIGITAL PRINTING – a system where the printed sheet is directly linked to a computer so there is no need to produce a printing plate, designs can be easily customised and changed FLEXOGRAPHY – used to print cartons, packaging and point of sale materials, used for ling print runs at low costs OFFSET LITHOGRAPHY – image is not printed direct from a plate but offset first on to a rubber covered cylinder which performs the printing operation. The system is based on the principle of water and oil not mixing. Generally used for long print runs. PRINT RUN – the number of copies to be printed at one time PROCESS COLOURS - cyan is a shade of blue, magenta is a shade of red, yellow and black. These are combined in four colour printing processes to produce a full colour image. REGISTRATION MARKS - crossed lines printed around the edge of a design that need to line up when each colour is applied in order to create a clear image WEB FED - printing on to a continuous roll of paper rather than single sheets SHEET FED – pre cut paper is fed in as individual sheets in to a printer.

CMYK: Four colour printing – process colours Only four colours are needed to reproduce the millions of colours visible to the human eye when printing. Cyan Magenta Yellow BlacK Any colour can be reproduced using a combination of these colours. These four colours are usually refered to as CMYK. Before any picture is printed is has to be 'seperated' into these four colours. This is unsurprisingly called colour seperation.

The centre image has been divided onto the four colours need to print in full colour.

Printed images are usually made up of millions of tiny dots of colour placed close to one another. You can see these if you look closely at a photo in a newspaper. When you stand back away from the image you can no longer see the individual, CMYK dots but millions of different colours. Colours can also be reproduced by overlapping the four colours as the inks are slightly transparent. Cyan put on top of yellow will appear green. Why is a K used to represent black? Wouldn't B be better? When we talk about making a colour with light we only need 3 colours, RGB, Red, Green and Blue. These are the three colours used to make the colour pictures on your tv, if you look closely as the screen you will be able see the RGB dots on the screen. The initial 'B' is used here to refer to blue. It would be confusing if it also meant black.

When full colour products are printed each of the four printing colours are added separately. C M Y K The yellow is printed onto the paper, then the cyan and so on... Each colour is added to the paper in a different part of the machine. The paper travels from the yellow printer to the yellow and so on... It is important that each colour is lined up exactly with the previous colour... Registration marks are used for this... They are usually a cross with a circle around it. They are printed 4 times, one in each colour over the top of each other... If the colours are lined up accurately you should only see a black registration mark. If one of the colours are out of line you will see that colour registration mark printed slightly to the side of the black registration mark... If the colours are out of line the final image will appear blurred. When printing a lot of something the registration marks are checked every so often to avoid reproducing a lot of errors.

The registration mark above (called a colour bar) is often found on the edge of products. It shows the Printer at a glance whether one of any colour has run out. It may be hard to tell by looking at the image. These registration marks are often cut off of the final product, though are often visible of newspapers or maps.

ProcessApplicationsAdvantagesDisadvantages Lithography More info... Magazines Posters Cereal boxes High quality, Prints photos and text Widely available Expensive to set up Only suitable for long production runs Gravure More info... Expensive packaging Stamps Very high quality Prints photos and text More expensive than Lithography Screen Printing More info... T-Shirts Printing on to products such as TV remotes and walkmans Can print on uneven surfaces Can print onto object that will not fit through a printing press Can be used for batch production Only prints simple shapes Will not print fine detail Flexography Carrier bags Yogurt pot lids Can print onto plastic films and foil Cheaper to setup than lithography Lower quality than Lithography Letterpress More info... Books with large amounts of textVery sharp letter quality Only suitable for letters and line drawings. NOT SUITABLE FOR PHOTOS

Lithography The process has a printing plate, with the image in relief which is free to rotate. Ink is applied to the printing plate which is dampened. This repels ink of any non image areas. The printing plate then transfers an inked image onto the rubber blanket cylinder which in turn presses the image onto the paper as it is fed through. Areas to be printed on attract the ink (grease) and areas not to be printed on attract water. High speed and cheap, most common used method. Print in full colour. 4 colour process called CYMK process (yellow, cyan, magenta, black.)

Lithography

Digital Printing This type of printing does not need printing plates as a computer is linked directly to a printing machine It is cost effective for small print runs and the work being printed can be modified easily Digital printing produces less waste in terms of chemicals The ink does not soak into the product but it forms a thin layer on the surface making the product easier to recycle

Flexography Used on corrugated containers, folding cartons, paper sacks, plastic carrier bags, milk and juice cartons, sweet wrappers and labels Most common form of printing for packaging due to lower quality needed and lower production costs A flexible plate, which has the images to be printed raised from its surface, is produced and attached to the plate cylinder. The material being printed is fed into the printing press on a roll. Ink is transferred onto a roller with a dimpled surface that transfers the ink to the plate and finally on to the material to be printed. Each stage of the process prints a single colour. The inks used for flexography are different than those used for lithography. It can print onto a variety of materials, inks dry quickly therefore production is quicker resulting in lower costs.

1 screen printing. No fine detail, small production run, cheap to set up 2 gravure. Very high quality needed 3 letterpress. Very sharp quality, no pictures needed 4 lithography. High quality colour picture needed 5 lithography. High quality cd inlay needed in full colour 6 screen printing. Can print onto rough/uneven surfaces