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Printing Techniques

I know that our blog contains a references to different printing techniques.  We probably know what we are talking about and don’t provide any explanations.  This idiot’s guide to printing technology (the idiot in this case is probably the author) provides a quick reference to the four main ways of producing a printed image.   If you want to know more a good place to start is the collection of articles on the history of printing in  Wikepedia.

Letterpress printing is probably the oldest technique of them all.  Intuitively carving an image out of a block of wood, coating it with ink or paint and pressing it onto a sheet of paper is an obvious way of making multiple copies.  This technique predates Gutenberg and was in use in China by 868AD.  By the 14th century printing on cloth using wooden blocks was carried out in EuropeJohannes Gutenberg’s critical innovation was the development of metal type which together with the availability of paper made letterpress printing possible. The appearance of the 42 Line Gutenberg Bible in 1455 marks the introduction of letterpress printing which dominated the business for over 500 years.  The essential characteristic of letterpress is that the black part of the image is raised.  Throughout the time that they were in business Robert Smail & Sons was primarily a letterpress printer.  The many cases of type in the case room and the collection of over 1,000 printers blocks that provide the illustrations all have the black part of the image raised.

Whilst letterpress printing is no longer used for everyday printing it lives in rubber stamps and dot matrix computer printers which are still used to produce invoices and other similar documents where it is necessary to produce multiple copies simultaneously.  In the world of arts and crafts limited edition books are printed by letterpress as it has a tactile quality not available by other means.  Lino cuts, stamping and the humble potato print all utilise this approach to the printed image.

Intaglio printing   (Italian for "cut in") is the direct opposite of letterpress.  The image is incised into the surface of the printing plate.  The plate is coated with ink, the excess ink is wiped from the surface of the plate leaving ink in the incised image.  When a sheet of paper is pressed onto the plate it removes the ink from the incised image.  Intaglio might not be as intuitive an idea as letterpress but it first appeared in the 15th century.  It may have originated with goldsmiths taking an impression as a way of recording an engraved design.

Intaglio plates are expensive and time consuming to prepare and once the job is finished they cannot be re-used.  The results however are excellent and if deeply incised the thickness of ink transferred to the paper leaves a raised image that can be felt.  Consequently intaglio printing was used by for high quality work and it is still used to print bank notes and postage stamps.  Engravings and etchings created by artists such as Albrecht Durer were intaglio plates.  Whilst engraving or etching are sometimes used as synonyms for intaglio both techniques have been used to produce letterpress plates.  The wooden engraver Thomas Bewick was a prominent exponent of this approach.

Another conceptually simply way of reproducing an image is to cut it out of thin, stiff material and pass ink through onto the paper.  At its simplest this gave rise to the stencil, widely use for marking wooden crates and characterised by the bars that held the white in the centre of enclosed letters such as “O” in place.  A more sophisticated approach gave us the rotary duplicator made be Gestetner and Roneo.  Prior to the near universal introduction of plain paper photocopiers these duplicators were used whenever multiple copies of a document were required.  The text was typed, without a ribbon, onto a specially prepared paper stencil.  This cut the letters into the stencil and illustrations could be added with a stylus.  Ink could then be forced through the stencil onto sheets of paper.

Screen printing is the zenith of this approach to printing and the results are still all around us.  Printed T-shirts, glass and plastic containers and printed circuit boards all involve screen printing.  It is also a technique widely used by artists to produce multiple copies of a work and for the special effects that can be produced in no other way.

The basis of screen printing is a finely woven fabric mounted on a frame.  Originally this would have been made of silk (hence silk-screen printing) but now various synthetic fibres are used.  The fabric screen is coated with a non-permeable layer where no ink is to reach the paper leaving a fine mesh stencil in the image areas.  Ink can now be forced through the screen onto the substrate below using a squeegee.  The ink is sufficiently fluid that the individual spots formed by the mesh coalesce to give continuous blocks of colour.  Modern screen printing uses photo-sensitive materials to create the image allowing the impervious layer to be removed from the image area.  However screen printing was used by the Chinese in the first millennia but only reached Europe in the nineteenth century.  It only seems to have became widely used in the early twentieth century.

Conceptually the most difficult technology to understand lithography (literally stone writing) is the basis of most modern commercial printing.   It relies on the immiscibility of oil and water rather than surface relief.  The image is formed with an greasy material on a highly hydrophilic surface.  To print the surface is wetted, the excess water is removed and the image coated with ink which adheres to the grease but not the wetted surface.  When a sheet of paper is pressed onto the surface it picks up the ink to form the image on the paper.

Lithography first appeared in Germany at the end of the eighteenth century.  The original surface was a piece of highly polished Bavarian limestone - hence the name.  The image had to be hand drawn on the surface - in reverse.  For the next 150 years its use was largely restricted to high quality artwork and illustrations.  Two twentieth century developments allowed lithography to become the near universal printing technology that it is today.  The first was the development of offset lithography (offset litho).  In this process the ink is lifted from the image on the litho plate by a rubber blanket and then transferred to the paper.  Now the plates could be made of lightweight metal and the image did not need to be reversed on the plate.  Rotary presses meant that printing speed increased and the production of plates was ideally suited to photo-typesetting.  Add computers to produce the plates and printing on a continuous roll of paper (web offset litho) and the result is high speed commercial printing capable of producing large numbers of copies rapidly.  The technology makes it easy to incorporate text and pictures into the same page and multi-colour printing is much simpler to achieve.  The consequence is that commercial offset litho has displaced all other printing technologies except for specialist and niche applications.

Plain paper photocopiers and laser printers make us of a very similar approach to printing.  Here the image is formed by light as an electro-static charge on a drum.  Toner (think of it as powdered ink) is picked up by the charged areas on the drum and transferred to the paper.  Heat fuses the toner to the paper to give a permanent image.

1 comment:

  1. T-shirt printing is my passion and profession both and I prefer Screen printing which is a technique that can entertain an extensive range of different materials. With this technique printers can produce tshirts, promotional banners, hats and even posters all from the same screens.