I was doing 'magic' WOW mugs several times, but only with new delivery from (cut) I have small problems. Some of the mugs are end up with brighter streaks after they cool down. When the mug is hot, everything is great, just when cooling down you can see not all mug change back to black.
I'm pressing them exactly the same like before, 180s 180C. Is it possible that I put to much pressure on them? I do mugs different sizes and the pressure is not always the same (adjust it manually).
I've done 10 mugs, 4 of them where with those stripes/streaks.
Any ideas much appreciated

New here... Any help will be appreciated :)