Screenprinting

By far the most recent of the print media, screenprinting is basically a stencil process. A stencil is applied to a fine mesh (the screen) which has been stretched over a frame. Ink is then pushed, with a flexible-bladed squeegee, through the remaining areas of open mesh onto the paper below.

The screen can be prepared in many different ways. Here are three of the most common methods:

Hand-painted stencils can be made using propriety screen fillers. Interesting effects can be obtained by thining the fillers with water to form washes which can print as a half-tone.

Photo stencils are the most commonly used. An image is transferred or painted directly onto a sheet of grained acetate using photopaque paint. As a seperate acetate sheet has to be used for each colour, these sheets are known as 'separations'. A screen is coated with light sensitive emulsion which, when dry, is placed on top of the separation which has been laid on a glass topped table. A flexible rubber sheet is pulled over the table, screen and separation and air is evacuated by a vacuum pump ensuring a perfect contact. The screen is then exposed to ultra-violet light which passes through the glass and acetate to harden the emulsion. The opaque painting protects the emulsion behind it from light, allowing it to remain soft. The screen is then washed out with water and the soft parts of the emulsion dissolve away, leaving areas of open mesh through which ink can pass.

Photographic stencils are prepared in the same way, with a film being used instead of a painted separatin.