I have been making tumblers for a while with sublimation, but have been having this problem only on this one design. I'm trying to sublimate a black background design onto a white tumbler. Every time I do it I get white spots around the top and bottom of the tumbler. I've tried it 4 times and it happens every time. I'm rapping it super tight and using shrink wrap to seal it, then I tapped the whole thing. Nothing works. Has anyone had this same problem and what can I do to fix this?