a brief description of what is involved in screen printing
Screen Printing T-Shirts: the Process
a) The Screen
At one time this process was known as silk screen printing, because the screens used were made from silk. It was a popular printing technique in China, hence the silk, but modern polymer fibres now enable us to use synthetic screens which are considerably less expensive.
Although the artwork is needed before the screens can be made, an explanation of the technique will be necessary so you can understand the limitations in your design. First, a mesh is required with holes large enough to allow the ink to be squeezed through it. An average mesh will be 110 (110 threads/inch), with lower for thicker inks and block images, and higher for thinner inks and more definition.
The mesh is coated with a light-sensitive emulsion, and the artwork placed under it. Light is exposed up through the screen, and where the light hits the screen, the chemical solidifies and covers the mesh. The design area stops the light, so when the screen is washed, the area of the design is clear of emulsion, while the rest is solid. This is true whether screen printing t-shirts or any other item.
b) The Printing
The screen is mounted in a box, and the garment is placed under the box. Ink is poured into the box and a tool known as a 'squeegee' is pulled across, forcing the ink through the mesh. The ink is then dried, leaving the image on the t-shirt.
As you can imagine, this process is suitable only for a single colour per printing because only one colour can be poured in the mesh box or they would run together. For more colours, the process has to be repeated. Only delineated areas of individual colour can be printed, so it is not possible to merge one shade into another when screen printing t-shirts.
It should be apparent that a new screen is needed for each different colour unless the pattern is exactly the same. This adds to the cost, and screen printing t-shirts is expensive for individual garments. There is a fixed set-up cost and then an additional cost for each colour. The more t-shirts that are printed in a run, then the cheaper it gets for each individual garment.