Screen printing discharge ink is water based ink with an additive (Discharge Additive). You can add pigment (color) to your water based ink and also add the discharge additive to the ink to change the color of the fabric by "replacing" the color of the t-shirt with the color of the pigment in the water based ink. For example- a black t-shirt- to become a black t-shirt the factory used black "dye" to make the shirt black- and if we use red discharge ink- the red will bleach out the black dye and replace it with the red discharge ink. Discharge ink is mainly used for cotton shirts. But... we have used discharge ink on some 50/50 blend shirts. Using discharge ink has a very soft hand- plus you don't need to use an underbase white- you can print your colors directly onto the t-shirt.
Here are some pointers about screen printing with discharge ink.
Discharge inks require more air flow to dry or cure the inks than the standard plastisol inks do. To fully cure discharge ink you must force the water out of the inks before they can be cured by reaching the 320 degrees.
Discharge ink work best on dark cotton garments.
Discharge ink can be mixed with pigments to create specific pantone shades- but this can be very tricky, as some fabrics and dyes work well with discharge and others do not.
Discharge ink can "dry" in the screen- But there are additives to keep the ink "wet" longer- These additives have made printing with discharge inks much easier.
Discharge ink requires mixing