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Letterpress is one of the oldest forms of industrial printing. Letterpress is known as a relief printing method, because the printing plate is not flat.
A printing plate is prepared with the image to be printed raised above the surface of the plate, standing proud of the non-printing area.
The raised surface is coated with ink and is then pressed onto the paper.
It is an expensive process, as the plate has to be specially made and high quality paper is needed. It is used for high quality books and stationary.
Lithography is the most commonly used process in the printing industry.
The image is transferred onto the completely flat printing plate photographically, using UV light.
The plate is washed in a chemical that makes the image area attractive to the oil-based ink. The non-image area is dampened with water to repel the ink.
Lithography is used for medium to large print runs because the set-up costs are high.
Flexography Flexography is very similar to letterpress as it uses a relief plate. As the name suggests, the relief plate is made from a flexible material, like rubber.
It is used to print on unconventional materials, like polythene for packaging. Flexography is ideal for these surfaces, because the ink is mixed with a solvent that evaporates, causing the ink to dry quickly.
Flexography is used on carrier bags and some wallpapers.
Gravure is used to produce high quality photographic images. It is very good for reproducing fine detail. However, gravure is a very costly process due to the skill needed to manufacture the printing plate.
It is the opposite to letterpress – the printing areas are in fact lower then the non-printing areas. The image is engraved onto a copper plate, creating cells that are filled with a spirit based ink. The paper is pressed against these cells to produce the image. The ink evaporates quickly once printed.
Screen printing is completely different to any other printing method. It works by forcing ink through a stencil. The stencil shape reflects the image to be printed. The stencil can be made of paper or card and is supported by a fine mesh.
The ink is spread over the mesh using a spreader, and then forced through the mesh onto the surface to be printed. Stencils can be made fairly simply, but to create more complex images, a photographic stencil is required. These have to be made by a professional or using a computer.
You can add interest and impact to a graphic product by adding a printing effect. There are lots of printing techniques to choose from, but they can restrict your choice of materials and add to the final cost.
The designer can choose from the following printing effects:
Applying varnish to a product has two main functions:
Printing effects
Varnishing
Varnishing is done after printing but before any cutting, folding or trimming.
There are several different types of varnishing. Oil-based and water-based varnishes are sometimes used, but the most important types of varnishing are spirit varnishing and ultraviolet varnishing.
Quality is essential in all products – printed products are no exception. When a document or item is printed, a series of marks are created that allow manufacturers to check that the printing has been done correctly:
Registration marks
These marks allow printers to check alignment. If the colour plates are aligned properly, the mark will appear black.
Quality checks
Colour blocks Allow you to check the colour for correct tone and equal density.