That shouldn't be there....

[Get Canvas & Sublimation]

I experienced this before and the paper was picking up ink as it went through the printer, being an Epson ( top sheet feed) the heads must have left a very slight amount on ink on the paper as the carriage passes. I used different paper which solved this.

Also check your pressure, clamping in the mug at medium pressure to transfer

good luck

[Drix Productions]

Hi guys, thanks for all the advice and sorry for my late reply. I contacted my mug supplier after also finding that the ink was coming off in the dishwasher, even though it was guaranteed not to. They agreed that was caused by a bad batch of mugs but not the random black bits. They also said that any tiny hairs would be pressed into the mug and not be absorbed by the paper. So I guess I need to wipe and check every single mug very carefully to make sure no dust has fallen on them while I'm sticking the paper on! Its very time consuming but seems to be working! Thank you!