discharge printing

for screen printing with water-based inks on dark materials, printers will often use color discharge to remove the color beneath the ink to make the ink brighter. if you print white on black, for instance, you need to use discharge or you will have to lay down such a thick layer of ink that the shirt will likely stand on it’s own (you know that thick rubbery feel some shirts have? well i hate that).

i’ve found that discharge is useful for other reasons, but have had some time finding the right discharge. our shirts like the claw machine and got dirt use discharge to remove the black color from a screened on pattern. we then tie dye to create a unique design. we also sometimes use discharge to remove some tie-dye from a shirt like unicorn on rainbow. in those kind of shirts, the process is to tie dye first and then screen print with the discharge. here i’ll discuss some of the things we’ve found with discharge.

specs that shouldn't be there

specs that shouldn’t be there

dharma trading has a number of discharge products. one that i tried first was discharge paste. this stuff is a fairly good consistency for screen printing and does a decent job. one thing i noticed was if you don’t get the paste to penetrate the fabric, you won’t get as clear or consistent a white. also i noticed spots on some shirts. this might have been caused by inadequate washing (some fabric softener or something still on the fabric). since i saw the spots i started washing black shirts with the “extra rinse” setting on. this also seemed to work ok on some tie dye colors, but not really at all on others. colors like blue seemed to turn a strange grey instead of just a lightened blue. this forced me to re-think our logo shirt design. originally, i wanted it to have a darker blue sky area and then bring a white border around the image to set the color apart from the blue sky background. the grey color it turned really didn’t work so i had to go with a much lighter blue sky area in order to see the contrast of the green tree and the multicolor shirts.

later, i found some stuff from ryonet. their discharge base came in two parts, the base and the activator. oddly, you use 6% activator for the base but they sell the activator in quart sizes just like the base. also, the activator looked alot like the soda ash i use in printing. this stuff worked great, but had to be mixed and, once mixed, had to be used within 6 hours. this is a major problem for me since i make very few shirts at the same time. this means i’d be wasting much of the discharge every time i printed.

screen ink discharge

screen ink discharge

recently, while poking around the dharma site, i found screen ink discharge. as with the ryonet stuff, this is made for printing see through inks on a dark shirt. it is concentrated so that you can add 7% of it to your ink and then print in one step. once this stuff is activated by heat, it removes the existing color then the ink cures to create bright colors.

blue and green turns to an odd grey

blue and green turns to an odd grey

i got some and decided to try it out so i mixed it with some sodium alginate thickener and printed. the results were amazing. not only did it go lighter than the other products, but since i could make the paste any thickness i wanted, it really penetrated the material so it removed the color all the way through. i’m very impressed with this stuff. it still had the same problem with blue and green fiber reactive dye, but i’m excited to see how it does on oranges and reds. here is the recipe i use to mix up a 25% strength discharge for printing through a 110 mesh screen:

first, i make 2 quarts of thickener (i use this sometimes with tie dye so i always keep some around in the fridge):
1 ½ cup urea
5 tbs sodium alginate
2 quarts water

then to make the discharge paste, i mix 3 parts of the thickener above to 1 part of the discharge, so 2 cups would be:
1 ½ cup thickener
½ cup discharge

i’m not sure how long i can store this solution, but i wouldn’t guess it would go bad any sooner than the thickener would by itself.

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