Based on my experience, Speedball's Fabric Block Printing Ink (available through both Blick and Amazon) has performed well in the years since I originally printed the t-shirt. Especially considering that I made this shirt before I did a lot of testing in my printing process. For instance, I now always wash new fabric before printing and cure the ink in a hot dryer (I can't remember if I did either on this early t-shirt). I have a more recent shirt that I block printed after I honed my technique, which is holding up very well.
The shirts were always washed and dried with our regular laundry - no special care was taken with them. The intensity of the lino print still seems good to me. Like I mentioned in my original ink review, though, there is a little fading at the beginning. Don't be surprised when the intensity of the print's color is not as deep after you first wash it.
In my experience, after that initial fading, the ink's permanence holds up over the years. Given this, if the printed t-shirt is going to someone else, I recommend pre-washing the t-shirt once the ink sets, sort of like how companies pre-wash jeans before selling them. And, if you're looking for other printing tips, I have a whole page dedicated to the t-shirt printing process.
I hope this update has been helpful!