Screen Printing
The screen printing process is one of the oldest forms of printing – and one of the forms with the greatest future ahead of it. That’s because it’s a really simple idea that is easy to transfer to a huge variety of materials.
The essential idea behind screen printing is that a screen is used to keep the ink applied from colouring areas of a surface being printed: i.e. only areas that have been cut out of the screen allow ink through onto the substrate. In its simplest form, this principle is known to children as stencilling. In recent years, screen printing has become an important commercial process, and its often used to produce designer or customised items such as printed t-shirts.
How does screen printing work?
When it was first developed, screen printing used screens made of silk, hence the term silkscreen printing; but nowadays, the screens are made of synthetic polyester mesh. You have to start by pre-processing the mesh, which needs to be immersed in a purpose-mixed light-sensitive emulsion and left to dry in a dark-room. Once this emulsion has set, you place a dark print-out negative of the pattern you want to print, or non-transparent stencil cut-outs of it, on the mesh and expose it to strong light: the light hardens the emulsion further, but the dark colour or stencil cut-outs prevent the light from reaching the areas through which ink will need to be pressed. You then wash the screen off in water, and these non-hardened areas are rinsed away, leaving non-coated membrane gaps which can hold ink, but through which ink can also be squeezed.
The mesh screen is now ready to be used, so you set it up in a printing press, taped at the edges so that no unwanted extra paint seeps over the sides. The press both holds the substrate under the screen on a solid base and fixes the mesh. Once you have clamped the press down just above the surface to be printed, you pour a small reservoir of ink onto the screen and use a bar to pull the ink across the screen so that it flows into the non-coated membrane gaps: now that just enough ink is in the gaps, you press the screen onto the substrate and use a squeegee to force ink through the membrane. The substrate is now printed and you can remove it.
What about colours?
Now, of course, with the screen printing process, you can’t print two colours at the same time on the same surface: well, you could, but the result would be an interesting and unpredictable mix of the two colours. So you always need to print different coloured areas of the design one after another: some presses offer you several colour stations so that you can layer colour after colour without needing to unclamp the press and remove the mesh.
It’s also important to think about your inks. Especially if you’re printing a t-shirt, you’ll need the right ink for the fabric – i.e. are you printing onto light cotton or dark Polyester? And there is a range of different stylistic effects to be considered (e.g. inks with a suede finish, gloss finishes).
How do I design for screen printing?
The most important thing to remember here is that your design needs to work as a negative: i.e. you need to be able to make a cut of it in a dark colour to apply to the screen mesh during pre-processing – or, if you have a multi-coloured design, you need to be able to cut out segments of it and apply them to a range of meshes. Simple is good – think of artists like Andy Warhol, pioneers of modern screen printing, and the bold, simple designs made up of monochrome blocks and areas they used.