DIGITAL CERAMIC PRINTING
Screen printing involves stretching a mesh over a frame and applying a stencil to block out the areas not requiring colour. The ink is forced through the screen - using a flexible blade - and deposited onto the material to be printed. Screens are available in a range of mesh sizes, and a coarser screen will print a heavier deposit. For screen printing, a separate frame, screen and stencil is required for each colour and in order to make the stencil a positive film has to be made to mask off the print areas when the stencil is fixed to the screen. This is often referred to as the origination cost and can obviously make the process quite expensive for short runs. Ceramic screen printing inks though are much cheaper than the ceramic toners used in ceramic digital printing so for the commercial printing of ceramic transfers on an industrial scale screen printing is much more cost effective. The other main advantages of screen printing over digital are that a much wider range of colours are available which can be printed as much heavier deposits, and ensuring a consistency of colour is much more achievable.
Precious metals (gold and platinum) need to be screen printed and for glass transfers, screen printing will provide much stronger colours.
Ceramic transfer printing began in the mid 18th century. The first transfer printing involved printing onto tissue paper from engraved copper plates which were filled with ceramic colour. The printed side of the tissue was then pressed into the bisque ceramic ware and the tissue removed before firing. John Sadler and Guy Green from Liverpool, England, signed an affidavit in July 1756, certifying that they had used this process to hand decorate 1200 tiles in one day for Josiah Wedgwood.
Perhaps the most famous of all prints produced by this process is the 'Willow Pattern' engraved by Thomas Minton - whilst working at Caughley Pottery - but later popularised at his own 'Minton' pottery. The process is still in use in the 21st century most notably at Burgess and Leigh, also in Stoke-on-Trent.
It wasn't until the 1840s that the Pratt Brothers developed a process for multi colour printing onto tissue using a separate plate for each colour.
A lithograph process - invented by Alois Senefelder of Austria in 1796 - was later used for ceramic transfer printing. In the early form of the process the design was etched onto a polished limestone slab and used to transfer a varnish onto the tissue paper. This was then dusted with ceramic colours and the excess wiped off with lamb's wool.
In 1895 Brittains Ltd of Cheddleton, England, introduced the first duplex paper in which the tissue was adhered to a backing paper. This duplex paper replaced the need for zinc plates which previously supported the tissue during the printing process. After printing on the duplex paper the tissue could be stripped from the backing and applied to the ware as previously. Brittains (taken over by Tullis Russell in the late 1970s) continued to produce decal papers in England into the early 21st century when production was moved to South Korea.
Silk screen printing in which a silk mesh was stretched over a frame came to be used commercially in the 1900s and was used later in the 1930s to put down a lacquer coat on top of the print thus eliminating the need for the tissue as a carrier of the design. Ceramic transfers by this time were printed by an offset litho process (using cylinders to replace the stones) in which a varnish was printed onto a water-slide decal paper (made by Brittains) and dusted with ceramic powder to form the image. Multiple ceramic colours could be printed by this process before the final covercoat layer (the carrier) was applied by screen printing. By the 1960s the colours were also being screen printed and by the end of the century screen printing had almost completely replaced offset litho printing for the production of ceramic transfers.
The introduction of colour laser printers and photocopiers in the 1980s facilitated the development of digital ceramic printing. Michael Zimmer in Germany was one of the early pioneers of the system, incorporating ceramic colours in a thermoplastic medium which could be finely ground into a toner for use on a Canon CLC 700 printer. The technology has improved significantly since those early days and there are now a wide range of ceramic toner systems available for firing both onglaze and inglaze.
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