Silkscreen Printing is a printmaking technique that traditionally creates a sharp edged image using a stencil and a porous fabric. A screenprint or serigraph is an image created using this technique.It began as an industrial technology, and was adopted by American graphic artists in the 1930s; the Pop Art movement of the 1960s further popularized the technique. Many of Andy Warhol’s most famous works were created using the technique. It is currently popular both in fine arts and in commercial printing, where it is commonly used to put images on T shirts, hats, ceramics, glass, polyethylene, polypropylene, paper, metals, and wood.In electronics, the term screenprinting or screenprinting legend often refers to the writing on a printed circuit board. Screenprinting may also be used in the process of etching the copper wiring on the board.Graphic screenprinting is widely used today to create many mass or large batch produced graphics, such as posters or display stands. Full color prints can be created by printing in CMYK (Cyan, Magenta, Yellow and Black). Screenprinting is often preferred over other processes such as dye sublimation or inkjet printing because of its low cost and ability to print on many mediums.

Screenprinting has its origins in simple stencilling, most notably of the Japanese form (katazome). The modern screenprinting process originated from patents taken out by Samuel Simon in the early 1900s in England. This idea was then adopted in San Francisco, California, by John Pilsworth in 1914 who used screenprinting to form multicolor prints in much the same manner as screenprinting is done today.Screenprinting took off during First World War as an industrial process for printing flags and banners. The use of photographic stencils at this time made the process more versatile and encouraged wide spread use. The term silk screen has not been in use within the industry since the mid 1940s when the use of silk was discontinued because of its use in the war effort. Since that time, screenprinting has used polyester material for the screen mesh.Screenprinting was pioneered at the Jepson Art Institute by printmaker Guy McCoy, who was among the first to develop the techniques of silk screen printing as a fine art medium. Herbert Jepson was also the founder of the Western Institute of Serigraphy.

A screen is made of a piece of porous, finely woven fabric (originally silk, but typically made of polyester or nylon since the 1940s) stretched over a wood or aluminum frame. Areas of the screen are blocked off with a non permeable materialâ€"a stencilâ€"which is a negative of the image to be printed; that is, the open spaces are where the ink will appear.The screen is placed on top of a piece of dry paper or fabric. Ink is placed on top of the screen, and a squeegee (rubber blade) is used to push the ink evenly into the screen openings and onto the substrate. The ink passes through the open spaces in the screen onto the paper or fabric below; then the screen is lifted away. The screen can be re used after cleaning. If more than one color is being printed on the same surface, the ink is allowed to dry and then the process is repeated with another screen and different color of ink.

While the public thinks of garments in conjunction with screen printing today there are tens of thousands of items being screenprinted, including birthday cake designs, decals, clock and watch faces, the electromagnetic faces of Palm Pilots and so much more. The vast majority of the time there is one ink color per screen.

A macro photo of a silk screen with a photographically produced stencil. The ink will penetrate where the stencil does not cover the fabric.
There are several ways to create a stencil for screenprinting. The simplest is to create it by hand in the desired shape, either by cutting a piece of paper (or plastic film) and attaching it to the screen, or by painting a negative image directly on the screen with a filler material which becomes impermeable when it dries. For a more painterly technique, the artist may choose to paint the image with drawing fluid, wait for the image to dry, and then ’scoop coat’ the entire screen with screen filler. After the filler has dried, a hose can be used to spray out the screen, and only the areas that were painted by the drawing fluid will wash away, leaving a stencil around it. This process enables the artist to incorporate their hand into the process, to stay true to their drawing.

A method that has increased in popularity is the photo emulsion technique:

The original image is placed on a transparent overlay. The image may be drawn or painted directly on the overlay, photocopied, or printed with a laser printer, as long as the areas to be inked are opaque. A black and white negative may also be used (projected on to the screen) However, unlike traditional platemaking, these screens are normally exposed by using film positives.

The overlay is placed over the emulsion coated screen, and then exposed with a strong light. The areas that are not opaque in the overlay allow light to reach the emulsion, which hardens and sticks to the screen.

The screen is washed off thoroughly. The areas of emulsion that were not exposed to light; corresponding to the image on the overlay â€" dissolve and wash away, leaving a negative stencil of the image attached to the screen.

Photographic screens can reproduce images with a high level of detail, and can be reused for thousands of copies. The ease of producing transparent overlays from any black and white image using a photocopier makes this the most convenient method for artists who are not familiar with other printmaking techniques. The low resolution and size limitations of a photocopier make film positives necessary in professional screen printing environments. Artists can obtain screens, frames, emulsion, and lights separately; there are also preassembled kits, which are especially popular for printing small items such as greeting cards.

Screenprinting is more versatile than other traditional printing techniques. The surface does not have to be printed under pressure, unlike etching or lithography, and it does not have to be planar. Screenprinting inks can be used to work with a variety of materials, such as textiles, ceramics, metal, wood, paper, glass, and plastic. As a result, screen printing is used in many different industries, from clothing to product labels to circuit board printing.

This information was taken from wikipedia