Shortly after we got home, I was working on trying to get the stain out. While going through the various laundry cleaning supplies, I accidentally dislodged the cap on a bottle of bluing solution. In case you didn't know, bluing is blue. Very blue. Normal use is to dissolve a tiny amount in a large bucket of water. Spilling directly on clothing is a Bad Thing. Now I had a large blue blob on the front of the shirt below and to the right (from my point of view) of the WSFS logo. Worse, it also immediately soaked through and splotched a bunch of places on the back of the shirt.
The instructions on the bluing said that in case of this sort of accident to soak the clothing in an enclosed container with a generous amount of ammonia and water. We didn't have either a sealed bucket or ammonia, so we went to Big R and bought both. Soaking the shirt overnight seemed to help, but it was still stained. We refreshed the ammonia-and-water solution and left it soaking some more. After a couple of cycles of this, it appeared there was no more progress to be made with ammonia. The last round was to rub a stain remover on the blue stains and run it through the washing machine (adding more ammonia). Again, it made a tiny difference, but there was still blue stains front and back. Time to try something different.
Ammonia having reached the limits of usefulness, I decided to try bleach. Yes, I know you must never mix ammonia and bleach!. I put the ammonia away, and after the last round of laundering the shirt with an ammonia mixture, tackled the stain with bleach. That means both household bleach in the bleach dispenser of the washing machine, and also a bleach pen. The bleach pen said to wash the shirt right away after applying, so I did so. This did actually make some difference, but it was still blotchy. On the grounds that the shirt was a write-off anyway, I applied more bleach-pen solution very liberally to the stains front and back and left it to sit overnight. The next morning, I was pleased and surprised to see that most of the stains were gone, even before washing. I ran the shirt through the washer again (bleach, soap, hot water, presoak), and then applied the bleach pen one more time and left it to sit for another day.
After multiple rounds of bleach-pen and washing in hot water and bleach, I finally succeeded in getting rid of the stain.
There might be a tiny little spot on this shirt, and another one on the back, but you'd have to know they were there and go looking for it with a magnifying glass. Somewhat to my surprise, the multiple trips through the laundry didn't cause the WSFS logo printed on the shirt to fade away either.
This was a lot of work, and it's possible that it would have been less expensive (counting the costs of cleaning supplies and all the runs through the washing machine) to just buy another shirt, which I think I could still do if I could dredge up the site where we put those logos back during the 1994 Worldcon, but I'm still happy I got it done.