Screen Print
Basics
A screen is basically a stencil held together by mesh, so with each screen you can apply just one colour at a time. To pring multi-coloured designs, each colour requires a separate screen.
Screens we use for t-shirts are usually 48dpcm, screens for graphic printing tend to be around 92dpcm. Keep this in mind when you start your design!
The first thing is, of course, to choose a design. We may take pictures, make sketches, and exchange them between the main artist, the graphic designer, and the printer, discussing the possibilities.(
Color Separation
To prepare a design for screen print, it needs to be reduced to a limited colour palette first. Take for example this picture of Frank E. (Lonesome Cowboys from Hell):
In this case, we reduce the image to two colours only. The easiest way to do this is with image editing software (such as The Gimp, Photoshop, etc.). There is a function called "posterize". In our case, the image got reduced to only two colours (red, and white) on a pitch black background:
When screen printing on a black t-shirt, we need to print white and red separately. So from the above picture, create two pictures, one per channel.
Note that the white channel here includes the red channel? The resaon is, that we will be printing the white layer first, and then the red one on top. So in this particular layout, the red will be on top of a white background print. That will make the red strong and bright.
In a last step, we convert these layers into pitch black. We must do this because the actual screen gets created by photographic exposure. Since we're not printing the background, we don't need it any more. Anything that is to be printed, we turn black. After that the channels look like this.
That's pretty much it. With these we can go to a print service place and get them printed out onto acetate - don't forget registration marks!