The printing technique involves the application of a non ink-soluble emulsion over a fine woven fabric stretched across a flat rectangular frame and tensioned very tightly, so that when the printing ink is pressed down using a squeegee, the ink passes through the holes in the mesh where there is no emulsion onto the substrate.
Traditionally, Silk was used for the mesh, today, a strong polyester mesh is used.
To get the artwork onto the mesh, Negative Film is used, and the image is 'burnt' onto the mesh when exposed to UV light. Just like traditional photography, the emulsion is exposed, then the un-exposed regions are washed away. Leaving the hardened emulsion (areas that will not print), and some clean mesh areas (areas that will print).
Screen Printing has more 'start' costs and 'set up' costs compared to other sign making techniques, however, once these cost are approved, the actual production speed is faster. When large numbers of signs or garments are required these cost are quickly dissipated.