Designing your own T-shirts and other apparel is a fun process and can be pretty simple. The first thing you need to know is what printing method you will be using for your T-shirts. The second thing you need is the appropriate software. As a graphic designer, I highly recommend the Adobe software. For the methods outlined in this article, you will require Adobe Photoshop and Adobe Illustrator.
Types of T-shirt prints
Transfers is a simple but cheap method of T-shirt printing. It consists of printing on a special sheet of paper and then transferring the design onto the t-shirt using a heat source such as a house hold iron or T-shirt heat press. This method is cheap and the transferred design will not stay very long. Sometimes you will notice chips and cracks after just a few washes. The advantage of this method however is that you can print full color designs in raster format.
The best method of T-shirt printing is Silk Screening. Silk screening consists of ink being pressed through templates called screens and applied directly to the T-shirt. This process is done once per color, so if your T-shirt has 3 colors, it must pass through 3 color screens. Once all colors have been screened on, the T-shirt passes through an oven of sorts where the ink dries and becomes permanent. Since inks are applied individually, the silk screen process requires vector graphics with a pre-determined number of colors. Usually no more than 4 colors otherwise your T-shirt would take way to long to produce and your production costs would go up considerably. Silk screening is also the best method for mass production since large printing companies have large silk screen machines that can produce many shirts in sequence.
Designing for Silk Screen
As mentioned previously, silk screen method requires vector graphics. To create vector graphics, you need a vector imaging program such as Adobe Illustrator. The problem is, many designers prefer to design in Adobe Photoshop as opposed to Illustrator, but Photoshop is a raster imaging software, not vector.
Luckily, there is a workaround. You can design your t-shirt in Photoshop at a very high resolution, flatten your image, copy and paste it into an Illustrator canvas and then use the Trace tool to convert the graphic into Vector. From there, you can separate your colors and save it in a Vector format such as .AI or .EPS. The trace tool is not perfect but works quite well for this application.
When designing your T-shirt in Photoshop, make sure you stick to only a few colors. Avoid any shades and gradients in your T-shirt design.
When creating your canvas in Photoshop, fill the background layer with the desired color of your T-shirt
When using the Trace tool in Illustrator, set the amount of colors to the number of colors on your shirt + the background color. Once the design is vectorized, delete the background color.