Screen printing
Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mesh apertures with ink, and a reverse stroke then causes the screen to touch the substrate momentarily along a line of contact. This causes the ink to wet the substrate and be pulled out of the mesh apertures as the screen springs back after the blade has passed. One colour is printed at a time, so several screens can be used to produce a multi-coloured image or design. Traditionally, silk was used in the process. Currently, synthetic threads are commonly used in the screen printing process. The most popular mesh in general use is made of polyester. There are special-use mesh materials of nylon and stainless steel available to the screen-printer. There are also different types of mesh size which will determine the outcome and look of the finished design on the material. The technique is used not only for garment printing but for printing on many other substances, including decals, clock and watch faces, balloons, and many other products. Advanced uses include laying down conductors and resistors in multi-layer circuits using thin ceramic layers as the substrate. History Origins Screen printing first appeared in a recognizable form in China during the Song dynasty (960–1279 AD). It was then adapted by other Asian countries like Japan, and was further created using newer methods. Adoption in the West Screen printing was largely introduced to Western Europe from Asia sometime in the late 18th century, but did not gain large acceptance or use in Europe until silk mesh was more available for trade from the east and a profitable outlet for the medium discovered. Early in the 1910s, several printers experimenting with photo-reactive chemicals used the well-known actinic light–activated cross linking or hardening traits of potassium, sodium or ammonium chromate and dichromate chemicals with glues and gelatin compounds. Roy Beck, Charles Peter and Edward Owens studied and experimented with chromic acid salt sensitized emulsions for photo-reactive stencils. This trio of developers would prove to revolutionize the commercial screen printing industry by introducing photo-imaged stencils to the industry, though the acceptance of this method would take many years. Commercial screen printing now uses sensitizers far safer and less toxic than bichromates. Currently, there are large selections of pre-sensitized and "user mixed" sensitized emulsion chemicals for creating photo-reactive stencils. A group of artists who later formed the National Serigraph Society, including WPA artists Max Arthur Cohn, Anthony Velonis and Hyman Warsager, coined the word "serigraphy" in the 1930s to differentiate the artistic application of screen printing from the industrial use of the process. "Serigraphy" is a compound word formed from Latin "sēricum" (silk) and Greek "graphein" (to write or draw). Historians of the New York WPA poster shop give sole credit to Anthony Velonis for establishing Silkscreen methods used there,