There are a bewildering array of printing methods and processes available, more than you think. You may have even seen some nice design work, business cards or something and thought ‘That’s nice. So how have they done that?’
Well, I hope that by pointing out some of the common printing methods and finishes you’ll know what to ask for and a little about how it was done. I must stress that you’ll know ‘a little’ as there’s too much to go into here (those of you who really know your printing processes may shudder at my rather blunt descriptions.) This is more of a guide to uses and what end product you can expect.
Screen printing uses a squeegee to push ink through a mesh screen on which there is a stencil. This can really give a nice end result, but don’t expect nice clean lines. Not suitable for work with lots of detail, this gives a nice bold finish and each colour is added separately. The colours seldom line up together, over-lapping or leaving slight gaps. A great retro finish.
You will have used one of these at some point in your life, photocopiers work on the same principles. In simple terms, a laser is fired at a photoreceptor cylinder, creating a static electric image on it. This surface is exposed to toner (a mix of plastic powder and colour agent) which attracts the fine particles. This cylinder is then rolled over the paper, transferring the toner from the cylinder to the paper. Multiple passes are used when the print involves the use of colour. A pass for each of the toner cartridges, hence the longer time required to print colour images.
The paper is passed through a fuser assembly which heats up the paper and toner so that the plastic within the toner melts and bonds to the paper.
Another printer type that you will have used, and possibly been frustrated with. As the paper is passed through the printer, the print-head holding the different ink cartridges (usually 4, CMYK) passes left to right, depositing tiny spots of ink from each colour cartridge in the relevant quantities required to generate the required colours.
A technique that you will have seen used on t-shirts. The image is either printed onto or made out of a material that when heated, will bond to the item. There’s lots of different types of materials that can be heat-transferred, such as embroidered patches, vinyl lettering and DIY heat-transfers where using an Inkjet printer you print the images on the substrate and then apply the image to a t-shirt using an iron.
Woodblock / Woodcut Printing
A precursor to the letter-press technique, woodblock printing is essentially the same idea. This method was used around the 18th Century in different parts of the world. A block of wood, often beechwood or cherry wood in Japan, would be engraved, removing the elements which were to remain white (unprinted) and leaving the areas to be printed untouched and level. Ink would be applied to the surface before the block was then stamped or pressed onto the material that was to receive the print.
Incredible detail is possible and this technique could quite feasibly be used as laser engraving means that blocks can be produced easily and quite cheaply.
As woodblock printing, the method is quite similar though the ‘blocks’ are made up of individual type pieces or specially made decorative elements that are assembled and held together in a frame.
The frame and paper would be placed in the inked-up press and rollers transfer the ink onto the paper. Again, the use of more than one colour would usually require another frame unless you were going for some interesting effect.
The image is first transferred (offset) onto a rubber sheet from an etched plate. This image is then offset onto the paper. The technique is used for newspapers, magazines etc. when high-speed, large runs and consistent quality is needed. Commonly used with Lithography Printing (See below)
Lithography uses simple chemical processes to create an image onto a plate. Lithography works because of the mutual repulsion of oil and water. A photographic negative of the desired image is placed in contact with emulsion and the plate is exposed to ultraviolet light. The image on the plate emulsion can also be created by direct laser imaging in a CTP.
The plate is affixed to a cylinder on a printing press. Dampening rollers apply water, which covers the blank portions of the plate but is repelled by the emulsion of the image area. Ink, which is hydrophobic, is then applied by the inking rollers, which is repelled by the water and only adheres to the emulsion of the image area. A rubber blanket squeezes away excess water.
Pad printing is used to print onto objects, such as promotional gifts, where traditional printing methods would be unable to handle the item that is receiving the image.
The process uses a ‘pad’ that is shaped for it’s intended substrate. The pad is stamped on to a plate with the engraved image, depositing the ink on the pad. The pad then stamps the image on the object.
Thermographic printing is achieved by using a thermographic/embossing powder, made from plastic resins. The areas selected for raised printing are printed with slow-drying inks that do not contain dryers or hardeners so that they remain wet during the application of thermographic powder.
Excess powder is then removed, usually by use of a vacuum system before a radiant oven is then used to heat the remaining powder (resin), causing it to melt and bond to the substrate.
This process leaves a glossy, unevenly-raised print on the substrate.
Not to be confused with the above, this technique does use heat, but to cause a reaction in the special paper, thus creating the image.
The paper is specially developed to react to heat, most commonly shop till receipts, fax machine rolls and labels. Ever put a hot cup of coffee down on a fax and seen it’s a left a black impression of the bottom of the cup?
Only produces black and white images.
This method uses a flexible, 3D relief plate on a cylinder, again the image is transferred onto a substrate that passes over the cylinder. Typically this technique is used for printing onto non-porous surfaces such as plastic, and can produce continuous images, think wallpaper or wrapping paper.
The Anilox Roller makes Flexography unique. The Anilox Roller meters the predetermined ink that is transferred for uniform thickness. It has engraved cells that carry a certain capacity of inks that can only be seen with a microscope.
You probably won’t know the name, but you will have seen this used. Do you remember those ‘animated’ pictures that were usually found as a give-away in cereal boxes? Well it’s that.
A lenticular is an array of magnifying lenses, designed so that when viewed from slightly different angles, different segments of the image below are magnified. S the technology has improved, more and more ‘frames’ can be included, producing much smoother animations.
Big brands have gone back to this technology in very recent times, producing large (A0) posters using this method. The effect can be quite stunning and can avoid seeming cheap/cliché.
Rotogravure cylinders are made of copper plated steel or aluminium that is engraved or etched and then chromed. A cylinder is required for each colour, usually 4 (CMYK.)
Similar to other printing methods, the paper is passed over the cylinders, being dried between each, to build up the image. Rotogravure is an industrial print process, producing consistently high-quality images for a large number of impressions. Not suitable for short-runs.
Think of this as half-photography, half-printing. It produces those very vivid, slightly unreal photos and was widely used before colour photography was available.
Coloured gels were used to project the image onto tablets of stone and the images etched, to produce a stone based printing tablet. Between 4 and 19 of these tablets were produced for a single picture and then used with up to 19 different coloured inks to print the image.
The tablet of lithographic limestone is coated with a light sensitive coating. A reversed half-tone negative is then pressed against the coating and exposed to daylight causing it to harden. The coating is then washed in turpentine solutions to remove the unhardened bitumen and retouched.
This effect would be easily faked. Certainly easier than trying to reproduce the technique.
Using 6 colours instead of the usual 4 means that the colour spectrum / gamut can be increased. It allows enhanced visual impact as well as allowing for special colours to be introduced to a print run.
Spot colours are pre-mixed, true-colour inks used for printing. The CMYK method builds up the colour on the paper using various amounts of the corresponding inks.
The benefits of spot colours is the quality of the finish, and getting a specific result. Some colours(mainly shades of purple in my experience) struggle to print well in CMYK, particularly if used as block colour, leaving you with an uneven tone.