A brief history of  Silkscreen printing
Also known as Serigraphy; from the Latin word for silk: "Seri"
and the Greek "graphien" (to write or draw).

Early origins.
Silkscreen Printing has its origins in Asia as early as 2500 B.C. as a form of image repeat using sealed cloth and dyes,  but the screen printing process that we know today stems from the patents taken out in 1907 by Samuel Simon of Manchester. He used silk stretched on frames  to support hand sealed stencils. 

In 1914 John Pilsworth of San Francisco also took out a patent for multi color printing using the screen process, employing early industrialized mechanization.  During the First World War in America screen printing took off as a commercialized printing process; it was mainly used at first for flags and banners but also for 'point of sale' advertising in the dept. stores of America, which were evermore embracing graphic advertising.

Around this time the invention of the photographic stencil  revolutionized the process.  In the following years, dramatic  improvements were made in the presses, inks and chemicals used.  The introduction of computer technology in the 1980's changed the pre-press side of screen-printing, but the photographic method of "sealing" the "screen fabric" remains much the same.

Many practical applications
It is the broad variety of screen thickness/ink thickness that has given screen printing a unique place among all print processes.

Examples of screen printed items are everywhere.   It is still a primary method for traditional signage, decals, banners, and POP.  Many appliance control consoles and panels are multilayer  printed switches and graphics combined.  The printed and etched circuit boards in electronic equipment, flat panel glowing displays in cell phones and dashboards, flexible circuits,
antennas, and digitizers all utilize screen printing as a manufacturing  step in product construction.  Of course, the oldest and most well  known application is the use of screen printing to decorate clothing, fabrics, and soft-goods.

Fine artists have also used screen printing as a medium for expression, especially since the days of pop art in the sixties.  Andy Warhol is one of the few well known examples. These artists opened up a whole new vista in the use of the screen process, and contributed to the development of a large, limited edition method of gallery marketing and distribution.  It is one of the only printing methods that can still be produced by hand if desired.

A brief description of the process.
A 4-sided frame is used with fabric mesh stretched over it. The mesh is coated with a light sensitive emulsion or film, which will eventually enable sealing non-image holes in the screen. The image that needs to be printed is output to a film positive.  This film and the emulsion-coated mesh on the screen are sandwiched together and exposed to ultra-violet light. The screen is then washed with a jet of water which washes away all the light sensitive emulsion that has not been hardened by the ultra-violet light. This leaves you with an open stencil which corresponds exactly to the image that was supplied on the film.

Now the screen is fitted on the press and is hinged so it can be raised and lowered. The substrate to be printed is placed in position under the screen and ink is placed on the top side of the screen, (the frame acts also as wall to contain the ink ). A rubber blade gripped in a handle called a squeegee (not unlike a giant wind-shield wiper) is pulled across the top of the screen; it pushes the ink through the mesh onto the surface of the substrate you are printing. To repeat the process the squeegee floods the screen again with a return stroke before printing the next impression.

This method is altered to fit the requirements of the object to be printed, and often is quite different from this same process adapted to fit the decoration needs of another type of object.
Some items require basic accommodations, other need to screen print with a high level of complex controls.

Bibliography
and further reading:

The Thames and Hudson Manual of Screen Printing by Tim Mara 1979

Screenprinting: water-based techniques by Roni Henning, published by Watson- Guptill 1994

Ken Tyler Master Printer by Pat Gilmour, published by Hudson Hills Press 1986

The New Guide to Screenprinting by Brad Faine, published by Headline 1989

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