What you have is either left over ink but its probably stain from the pigment.Don't panick!Try a citrus based ink cleaner before you strip the screen and if there is still a stain put some more citrus cleaner on and let it sit for awhile.I hope your using a power washer because it's going to help get that stain out easier.I use a Speedball Diazo emulsion kit and a generic waterbased textile ink for right now. I just bought a screen from dickblick and have made a couple sloppy prints (learning) but there is a black ink residue all over my screen. I can't get it off! My ink is waterbased, so it should wash off with water but it doesn't. On my emulsion remover bottle it says that leaving ink residue on the screen while using the remover will ruin the screen. Oh boy. Money is tight and I would hate to see a $25 dollar screen ruined.
Has anyone been through this?