Discharge printing has seen a little coverage in this blog already, but deserves its own post.
If you remember, in the post about water-based inks, we discussed how water-based inks dye fabric, rather than laying ink over them. Discharge printing is a variation on water-based inks.
A chemical discharge agent is added to the dye, which removes, or discharges, the original dye of the fabric. All fabrics have a natural color in their undyed state. The discharge agent brings the fabric back to that state, but only in the dyed area. The effect is a lot like bleaching cloth.
Simultaneously, the ink is adding its own color to the discharged area. With plastisol screen printing, an underbase of white ink is often used to provide a light background on which darker colors appear more vibrant. The discharge process accomplishes a nearly identical effect.
Just as other water-based inks only work on hydrophilic fabrics like cotton, discharge printing only acts on the same fibers. The best discharge results happen on pure cotton garments, but the process can be used on cotton/polyester blends. Print quality decreases as the percentage of polyester rises. The result is that with blended fabrics, the print never has the vibrancy it would show on a cotton shirt.
There are some additional limitations. Not all cotton fabric dyes are reactive with discharge inks. The information is pretty easy to find in most cases, but if there is any doubt, the fabric should be tested before production.
The discharge process looks somewhat different than plastisol screen printing as well. The process of screen printing is more or less the same, though water based inks are much harder on screens, and need to be washed immediately, before the ink clogs the screen.
Discharge doesn’t just happen at any temperature. The process only starts to work between 350 and 370 degrees Fahrenheit. That’s a pretty warm day at the beach. After applying the discharge ink, the shirts are placed in a gas dryer, which pushes the temperature up to discharge range.
What makes discharge printing so popular?
Instead of seeing this as a limitation, printers exploit the interesting effects of seemingly unpredictable interactions. Printers are pretty familiar with the complex mix of variables that includes the original dye, the discharge agent, and the water-based replacement ink.
Of course, discharge prints aren’t for everybody. There are some drawbacks to discharge printing.
Discharge printing shouldn’t be considered an alternative to plastisol prints. There are some things that plasitsol does better, like detailed gradients. Instead, look to discharge printing to create unique prints with a classic look and feel.