Problems printing onto ceramic coasters

[Map1984]

Hi, I'm having some issues printing ceramic coasters. I get on fine if it's a simple design without too much ink, the lines are clear and vivid, but on designs with large blocks of dark colours I get a patchy and mottled effect. Any thoughts would be great, thanks in advance.

[ZoeCF20]

Hi, what kind of press are you using and what time/temp?

[Map1984]

Hi, it's a stahls /hotronix clamshell, fiddled around with settings a bit and using 205 deg C for 3 mins (with silicone mat), the results are getting there, sometimes great, but I'm still getting a weird effect, generally on black parts, where the ink seems to go a bit lighter, almost speckled green towards some of the outer edge. Thanks for your help

[gazfocus]

Are you pre-pressing the coasters for a few seconds? Are they glossy or matte?

[JMugs]

I always printed mine upside down on a foam base (I can't remember what the foam was called), also did the same with ceramic tiles.
The heat spreads more evenly when working upside down. You would need to juggle with the time / temp but it always worked for me. This came about as a result of a chat with some very charming lady at Conde in the US, she also said said lower temperature and longer gave more consistent results then hot and quicker, and she was right!

Janners

And a silicone mat on top.