Once your done with printing you need to heat set the ink for permanency so your print will last (hopefully) longer than your actual tee will. In screen printing jargon we call this “curing” the ink.
What you need:
Heat emitting object – iron, heat gun, flash unit
A fan – because it gets kinda warm
Depending on the type of paint you use (water-based or plastisol) you might need to run a few tests to determine the ideal ink-set temperature and time. I’ve used both water based and plastisol but have over time gone water-based exclusively. Water based inks heat sets faster, softer to the touch without additives, and is better for the environment. Whereas plastisol contains oil and requires higher temperatures to heat set (check with your ink supplier for the recommended temp), but is also cheaper and I can pretty much leave the extra ink on my screen overnight as it doesn’t dry up compared to water-based inks.
For my water based inks, I use a heat gun for the initial curing process. Once my image is dry enough, I place an iron over the image for another 25-30 seconds for good measure.