Sitting comfortably and got some time on your hands…?
The actual screen itself is an aluminium frame upon which a nylon mesh fabric has been tightly stretched & fixed onto. The flat “back” of the screen which sits on the printing surface is called the “print side” – or “paper side” – and the “front” of the screen, recessed inside the lip of the frame, is called the “squeegee side.”
Checking the screen first, prior to coating with emulsion (under light-safe conditions)
Each colour used within any screen printed design requires a separate stencil – with each stencil then requiring a separate piece of black artwork representing each individual colour separation. Screen printing only allows the printing of one colour at a time, so each sheet of paper has to be individually printed with each colour required.
Finished version of poster next to the separations used for printing each colour
The stencil is created by coating the screen with a photosensitive emulsion under a photosafe light in darkroom conditions. The coated screen is then left in the dark for 2-3 hours until it is completely dry. The artwork will be placed directly in front of this emulsion-coated screen, and to give as much close contact between screen and artwork as possible giving a clean, sharp image – a ‘print-down frame’ is used. This is a vacuum unit which enables the artwork to be held in perfect contact between a large sheet of glass and the screen, ready for the exposure process.
The screen exposed to UV light-source along with artwork in print down frame
The emulsion is hardened by exposure to UV light, so the artwork is used as a mask to block off certain areas on the screen from a controlled exposure to a high level, direct UV light-source. In areas where the emulsion hardens, ink won’t pass through. In those areas masked off from the light-source by the artwork, the emulsion remains soft and it will then subsequently be washed out of the screen, revealing areas of the fine nylon mesh through which ink can then pass.
It is through this process that an image can then be accurately reproduced onto paper by ink via a screen stencil.
The end of the first colour run, and the preparation (after exposure) of the screen – ready for printing the second colour of the poster
The screen is fixed in place (squeegee side up) to a printing bench – which is basically a counter-balanced, adjustable frame which is hinged along one side of a flat work surface – which can be easily raised up or lowered down to sit parallel with, just millimetres above, the work (or print) surface. The frame is counterbalanced to allow for an easy movement up and down and the print surface also incorporates a vacuum unit which prevents the carefully positioned sheets of paper slipping or moving during each print – which would cause mis-registration between each printed colour.
With the screen propped up slightly from the bench surface, a line of ink is applied along the top of the screen about 2 inches above the image to be printed. The stencil is then flooded with a coating of this ink, by pulling a squeegee down across the screen. The screen is then lowered and the first print is initially done onto a sheet of acetate, positioned & fixed onto the bench surface. This is used as a position guide for where the image will print – by accurately positioning the size of paper being used for the print run underneath the acetate. The screen is then slightly raised and immediately flooded with ink again to prevent the ink in the mesh areas from drying out and clogging the mesh.
Flooding the screen with ink, and initial pulls being checked for colour registration and image quality
With the acetate moved away, the screen is lowered to its printing position just above the carefully positioned sheet of paper, and the image is then printed onto the paper by pulling the squeegee across the screen at around a 45 degree angle – applying an even amount of firm pressure to allow the ink to pass through the screen. The screen is re-flooded with ink, and the printed image is then checked. The ink remains wet for approx 10 – 15mins, so each subsequent print is stacked in a drying rack to prevent contact between each one.
After all the preparation work involved, the actual print run is then just starting – with each print being done individually, and the whole process being repeated for each of the colours to be printed. Once dry, and the print run has been checked through, the posters are then trimmed to size and also signed and numbered.
