Screen printing is a printing technique with matrix, formerly called "crivellografia" from the “crivello- sieve “ (usually made of silk- hence the etymology), through which the ink passed.
The standard one colour process is roughly the following: having drawn the chosen picture on an acetate film, a robust and transparent plastic film, you put this sheet on the matrix made of a synthetic silk canvas, stretched over a frame, called "press", which in turn has already been coated with a photosensitive gelatin layer, distributed with the use of a special tool.
Then the outcome is put in a “vacuum bag” in order to guarantee the maximum grip between the two parts. This bag, in turn, is illuminated by a highly actinic light (5000W). This process is similar to the one used for the printing on offset plates.
The frame of the matrix is washed by a strong lukewarm water jet so that the gelatin, which was spread over the parts underlying the coloured parts of the picture, melts and sets the frame free.
Serigraphic
Art
Multiple color Screenprints need the use of multiple matrices (one per color) and a great precision in the overlay of the images, that can be obtained with the tracing of marks, which allow a very accurate printing.
The silkscreen technique normally produces flat images. You can get soft effects, using more sophisticated techniques and equipment. The press remains slightly in relief.
After drying the matrix, the frame is put in an automatic, semi-automatic, or manual silkscreen machine and you spread color print over it with the help of a rubber tool called “racla”. Where the matrix has been washed, the colour will pass through and impress on the paper. You can also print on a lot of other materials such as aluminium, steel, plastic, polypropylene, various fabrics, etc.