We started our business printing primarily with discharge inks. When I found out that I could get a bright color without using an underbase while printing on a manual press, I was sold. Over the years we have learned a ton of lessons. Occasionally we will have a new press operator printing a discharge job and realize the things we have learned from experience that we forgot to teach to them including…
Mixing Discharge: When looking at the ink formula for discharge, never use the full amount of white that is suggested. Start with 25-50% of the white that is suggested. White and black are both color killers. Once you add too much, you cannot remove it, so be very careful.
Discharge Agent: The more agent you use, the more pastel the color tends to look after discharging. Especially when we are discharging red inks, we use less agent. Usually around 3%.
Cleaning Screens on Press: This is a fun one. If you need to wipe down a screen on press, there will end up being discharge ink in places that you cannot see, but when you start printing again it will show up on your shirts in weird places. The biggest problem is often that discharge ink will build up around tape lines. Make sure to clean all of the tape lines well with a shop rag or a scrap shirt. Also always have a couple extra test shirts ready to print on, so that if there is any residue left, it will only screw up the test shirts.
Pot Life: Nothing to do with marijuana. Discharge ink has a limited life once the activator is added. It only lasts in the “pot” for six to twelve hours, depending on the heat and humidity. Some folks say up to 24 hours, but you really should not push your luck past one printing day at best. A trick related to that is that if you have white or light shirts to print in the run, save them for last and the ink will work on those even when the discharge agent has expired.
Print Order: If you are printing wet on wet, always put your white screen last. White discharge is the thickest and tends to build up on other screens really badly. In the pictures below you can see what happened when we setup a job recently in the wrong order. We printed white before other colors causing the white to build up on the following screens. After the white caked up, it came off in chunks on the following shirts. Not a good look as you can see.