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 small-scale commercial printing, where it is commonly used to put images on T-shirts, hats, ceramics, glass, polyethylene, polypropylene, paper, metals, and wood. Today, this service has been adapted for the web and there are many companies featuring online printing and quoting services.

In electronics, the term screenprinting or screenprinting legend often refers to the writing on a printed circuit board. Screenprinting printing may also be used in the process of etching the copper wiring on the board.

Printing technique
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 material—a stencil—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.

Stenciling techniques
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.

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 — 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.

Versatility
Screenprinting is more versatile than 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.

Information from Wikipedia, the free encyclopedia about screen printing equipment