Screen-printing

Screen-printing, also known as silkscreening or serigraphy, is a printmaking technique that creates a sharp-edged single-color 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. 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 and hats.

In electronics, the term silkscreen or silkscreen legend often refers to writing on a printed circuit board.

History

Silk screen printing has its origins in simple stencilling, most notably of the Japanese form. The modern silk screen 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 a silk screen to form multicolor prints in much the same manner as silk screening is done today.

Silk screening took off during the First World War as an industrial process for printing flags and banners. The use of photographic stencils at this time further increased the processes versatility and encouraged wide-spread use.

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 aluminium 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 spread the ink evenly across the screen. 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

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.

The most popular and flexible technique is to transfer a pre-drawn or printed image onto a screen using a type of photographic emulsion:

1. 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)
2. The overlay is placed over the emulsion-coated screen, and then exposed to a strong ultraviolet light. The areas that are not opaque in the overlay allow light to reach the emulsion, which hardens and sticks to the screen.
3. 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 hundreds 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. 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.

External links

• Museum of Modern Art information on printing techniques and examples of prints
• How does silk-screening work? from HowStuffWorks.com