Pretreament is a liquid solution used by Direct-to-Garment printers to allow the printing and washability of white ink, or full color images on a variety of colored shirts, most commonly black shirts.
The concept is simple. Just as drywall is primed with primer before painting, this primer allows the colored paint stay on top of the drywall and not soak in. If the paint soaks into the drywall, the color selected will be muted and off color.
The same is true with pretreating any DTG shirt. The pretreatment acts just like the primer in the drywall example. It allows the white ink printed through the DTG printer to adhere to and sit on top of the shirt. If the white ink soaked into the shirt, it wouldn't be white – more of a grey, and not give a smooth surface for the CMYK inks to print on, resulting in a really bad looking, unsellable shirt.
Pretreatment also reacts with the white ink. This reaction is similar to when a screen printer uses a “flash” unit to semi-cure the plastisol ink so the next colors printed on top don't smear or mix together (a result of printing wet-on-wet). The pretreatment “flashes” the white ink causing it to change properties and become more or less a semi-solid surface so when you print CMYK on top of the white ink, it doesn't mix and look muddy.
Pretreatment is the cornerstone of direct to garment printing. It is the foundation of your garment. A proper application of pretreatment will help yield better results for any white ink direct to garment printer.
Pretreatment is an aqueous solution, usually milky or clear in color, and designed to help the white ink sit on top of the shirt. Though it will not necessarily cause a reaction if you touch it, it is recommended to wear protective gloves, a respirator and other protective clothing just in case.
Pretreatment can be applied in two methods. The first is to apply the pretreatment by hand, using a Wagner type power sprayer. The issue with this application technique is that you are doing it by hand – resulting in less consistent application and amounts of pretreatment on the garment. The second is to utilize an automatic pretreatment machine (such as the Viper seen in the picture to the right) which allows the user to set the amount of fluid to be applied to the garment. The machine then applies the correct amount each time to the garment. This allows for much more consistent results and better DTG printing.