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A walkthrough of the need-to-knows of printing.
RGB & CMYK
Forgetting to convert an image from RGB to CMYK could result in a poor looking print job, and being aware of the processes involved in print production can prevent this error. As well as a potentially irritated client. Note that when converting from screen to print, the colours will not always be exact, but rather matched to the nearest colour within the respective gamut.
which are the 4 basic print colours, cyan, magenta, yellow and key (aka black) Black is added to give more definition and density to an area, which is essential to a full colour print job.
RGB is mainly used for screen, such as web design, as the colour spectrum, or rather gamut is nowhere near as vast as the gamut for CMYK.
When two of these colours overlap, we get what is known as “subtractive colours”, however when the combination of all these colours overlap, black is created, which is also known as registration black, as is used for registration marks.
Full colour is attained by breaking down the original image into 4 components
RGB are also known as “additive colours” because when all colours are combined they create white, which can only be viewed from a light transmitted source, for example the sun or a lamp.
Colour Seperation
halftone dots, traditional print methods, and tiny grids.
two colour printing
three colour printing
Traditionally, after seperating an image into the process colours, they would be prepared for silkscreen or what is known today as screen printing. In the days before imagesetters, platesetters, and scanners, seperation could only be done by photographic means. This requires making a negative for each of the colours, but for each of the subtractive colours, a filter of the respective additive was used to print. This was to ensure that all wavelengths of light reflected from the corresponding colour was not recorded on the emulsion used in the photographic process. When the plates have been made, it is imperitive that the rows of dots have to be put at the correct angle, else moire patters can occur. When printing in 4 colours, the following angles in degrees are: Black 45, magenta 75, yellow 90, cyan 105.
four colour printing
The halftone dots create a rosette pattern, which aids the eye to view the image as it was meant to be originally
The silk screens used were made up of a grid of tiny dots, so when it was printed, the human eye viusally mixes the coloured dots to reproduce all the colours of the original. The angles were detrimental to viewing the image, black was at 45 degrees, as it was the least visible angle to the human eye, as opposed to yellow, which was the most visible at 90 degrees. (see last page)
Colouring Images The nature of an image can instantly be changed and enhanced by merely changing the tone, filter or levels of the image in photoshop or other such photo editing software. Monotones are a single colour image, Duotones are two colour images, tritones are three colour images and quadtones are four colour images. First the image must be converted to grayscale, quite similar to the traditional method of making negatives for production. After this channels can be tampered with and colour levels respectively to bring out highlights and shadows within the image.
tones, tints and overprinting.
Full colour
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Overprinting is where an ink is printed over another to create another colour, a good example of this would be screen printing, or bad trapping where colours print on top of each other.
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Tints are used to maximize an images potential, and is a cost effective when considering a print job. They also help to keep an images uniformity, and give the image more strength, density and depth. They are also commonly found on packaging, alongside registration marks.
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Overprinting
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Tints and
Printing Processes
actions to take before commercial print
Before a job or piece of work can be sent off for printing, the choice of the print process is relative to the choice of print materials, as well as available resources.
Make-ready is a vital part of commercial printing, as the cist if the job, quality and the final outcome is dependant on this part of the process.
An application used in all the commercial printing is what is known as “makeready� which is all the actions taken on a press before the first good copies are produced.
Also known as reprographic printing, it offers a resource to clients and designers alike. The latest industry standard software enables us to automatically check and impose artwork easily before submitting accurate colour proofs in a digital format.
This includes setting the press up to accept the size and wieght of the substrate used, putting in the plates, sorting out the right ink and colour of ink on the press, adjusting the folder (see web-fed), and making sure the image is in the right position.
PDF workflow and CTP system are networked with the presses which allow the printers to pre-set colour data and important colour calibration information.
Printing Processes
Industrial & commercial
A majority of the processes require the paper to be either sheet-fed, or web-fed. The difference between the two being that sheet fed is when a print job is single sheets mechanically fed into a printer, whereas a web-fed printer is a continuous sheet of substrate, enabling a print job to be produced alot quicker, as it does not have to slow down to pick up a sheet. The predominant process used in printing today would be offset lithography, which uses huge rollers to feed paper through sheets of paper,
Dampening rollers
Paper
Ink rollers
Plate cylinder Blanket cylinder Impression cylinder
Sheet transfer cylinder
Printed image
The area is treated chemically so it accepts ink (grease) and rejects water, while the non-image (background) does the opposite. When the plate presses against the surface of the paper, it is only the image that is printed.
Offset Lithography Offset lithography has as many advantages as it has disadvantages, it has a brilliant image reproduction, especially of detailed images, but can sometimes have problems with colour variation due to ink and water balance. Thanks to CTP (computerto-plate), which esentially tarnsfers an image direct to the plate, which cuts down preperation time. To ensure the best possible outcome it is important that the designer talks to the printer. The printer is familiar with the process, their equipment, the type of plates, and file formats required for a job. Which is vital when printing en masse.
Using this particular process, a larger variety of substrate can be sued, such as a gloss, satin, matte, or just denser paper. This is due to the rubber blanket absorbing the pressure and texture on the substarte which can usually cause creasing or tearing, which leads to a botched job and a big headache for the designer, printer and client.
Flexography Flexographic printing was originally basic in quality. But due to technical advances in the past few years have all contributed to the quality of the flexographic printing press. The most noteable advancement in flexograpy have
been in the printing plates, including improvements to the plate material and how the plate is created. CTP has been a good improvement in the industry recently. Companies like Dupont, MacDermid, Kodak and Esko have pioneered the latest technologies with advances in washout and bringing screening technology to the next level. Laser-etched ceramic rolls are used now that greatly imrove the quality of print, full colour printing is now possible. Some of the finer presses, in combination with a skilled printer, produces a quality that rivals the lithographic process. One ongoing improvement has been the increasing ability to reproduce highlight tonal values.
Gravure
Gravure printing is an intaglio printing technique, which takes its origins from traditional methods such as aquatine, etching, engraving, and drypoint. The image is made up of small indents on the printing plate. The dents are quite like cells, which are filled in with ink, with the excess scraped off by what is known as a doctor blade. Afterwards a rubber roller presses paper onto the plate and into contact with the ink in the dents/cells. Printing process
plates are
made from copper and can be produced by digital engraving or laser etching. This method of print is primarily used for large scale, high end runs, for productions such as magazines, catalogues, packaging, fabric printing, postage stamps and plastic laminates.
Both Flexography and Gravure produce similar quality, however only a huge volume job makes a gravure print worthwhile, as flexography is cost effective for this for a smaller low volume normally job.
Substrate
what paper is suitable for the job?
When selecting, specifying then buying paper, careful measurements must be taken, when establishing the quality and quantity required. In the case of the client supplying the paper, the printer has to be consulted well in advance to ensure the equipment used will be able to take the substrate, and be able to go through the printing and finishing processes. Basic factors include; Weight, which is measured in gsm, for example, a retail flyer would be printed on something like 100gsm gloss, whereas an exhibition booklet would be on 160180gsm matte/gloss dependant on the context and content of the printjob.
Shade or tine has to be specified, as paper manufacturers often have their standard shades, with their own codes and names. But when a special shade or spot colour is required, its advisable to send a wide samples for colour matching purposes.
This is an example of what matte looks like, using offset litho process.
In some substrate they show different colours under certain lighting conditions, also known as “metametric� White, for some part of this reason, is the most difficult shade to match and specify.
Ink& Toner
print process determines choice of ink Despite paper being the major factor when considering print cost, the cost of ink is also vastly significant. Each printing process each requires specially formulated inks for that certain process.
Most inks are made by mixing the ingredients below into a roll mmill that breaks thm down until they have a smooth consistency.
The differences in the ink formulation for each process allows a certain press or substrate to be used, for example, toxicity issues in food packaging, drying requirements, printing onto a glossy surface, etc.
Pigment in powder form or dye, gives the ink its colour
Inks for gravure or flexography are liquid, and some are a paste, as those used in offset lithography. I will briefly outline types of ink, and thr processes within them to attain a print of high standard.
Resins form the binder for the pigment Liquids make the ink fluid so it can be transferred onto the rollers and blanket. Acts as a vessel for the finished ink to travel on Drying Ink The 5 main methods to dry ink are; evaporation, chemical curing, heat setting, penetration abd oxidation
Finishing
how to instantly give a publication or printjob an extra zing The only way to effectively describe and communicate what finishes are available is to show some examples. Keep in mind any of the following processes are best discussed with your printer before attempting them. This is a high quality flyer promoting drum and bass collective subfocus. Printed on high gloss 100gsm substrate, the finish used on this is called spot varnishing. This can be done on a press with a seperate varnishing unit added and with UV drying. Commonly found on books, cartons or anything with a brand or logo.
Another printjob for dance music promotion. This process known as UV coating, is similar to spot varnishing, except UV coating is applied, it creates a heavy, slightly raised relfective coating.
I finish with die-cutting. This is a process which involves a piece of work being cut mechanically, to ensure optimum accuracy, with a slick, crisp look. Used in a variety of contexts, but usually found on limited edition packagaing, or most recently dorset cereal packets.
Block print, hot stamp, heat stamp, foil emboss or foil stamp. These are all the same names for the same process. Involves a foil, or a coloured tape that is pressed onto substrate using a heat press. The transfer uses a die, or brass, which is bascially a different sort of plate in which to print with. Gives a job a professional look every time, can also be used in embossing or debossing.
All processes tha convert printed sheets into bound, folded and comleted publications are known as finishing operations. Always remember to check what colour you are using for a document, what sort of substrate will work with your design, what ink will work with your colour scheme, and finally, make sure the finished piece has something to remember it by.
Designed, published and edited by tommingsdesign. 2009