The most common form of commercial T-shirt decoration is screen-printing. In screen-printing, a design is separated into individual colors. Plastisol or water based inks are applied to the shirt through mesh screens which limits the areas where ink is deposited. In most commercial T-shirt printing, the specific colors in the design are used. To achieve a wider color spectrum with a limited number of colors, process printing (using only cyan, magenta, yellow and black ink) or simulated process (using only white, black, red, green, blue, and gold ink) is effective. Process printing is best suited for light colored shirts. Simulated process is best suited for dark colored shirts. Very few companies continue to use water-based inks on their shirts. The majority of other companies that create shirts prefer to use plastisol due to the ability to print on varying colors without the need for color adjustment at the art level.
Specialty inks trend in and out of fashion and include shimmer, puff, discharge, and chino based inks. A metallic foil can be heat pressed and stamped onto any plastisol ink. When combined with shimmer ink, metallics give a mirror like effect wherever the previously screened plastisol ink was applied. Specialty inks are more expensive to purchase as well as screen and tend to appear on garments in boutiques.
Other methods of decoration used on T-shirts include airbrush, applique, embroidery, impressing or embossing, and the ironing on of either flock lettering, heat transfers, or dye-sublimation transfers. Laser printers are capable of printing on plain paper using a special toner containing sublimation dyes which can then be permanently heat-transferred to T-shirts. In the 1980s, thermochromatic dyes were used to produce T-shirts that changed color when subjected to heat. The Global Hypercolour brand of these was a common sight on the streets of the UK for a few years, but has since mostly disappeared. These were also very popular in the United States among teenagers in the late 1980s. A downside of color-change garments is that the dyes can easily be damaged, especially by washing in warm water, or dye other clothes during washing. At the turn of the 21st century, designing custom T-shirts online became more popular. Popular websites began to use digital printing (such as Direct to Garment or DTG printing) to allow customers to design their own T-shirts online with no minimum orders. In the beginning, DTG could not print well on dark garments; however, with the help of some online T-Shirt retailers, printer manufacturers such as T-Jet have all but perfected the process, providing consumers with many more printing options.
Source :http://en.wikipedia.org/wiki/T-shirt
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