Ceramic tiles cracking

[ScotTs]

Hi, I've recently started printing on sub ceramic tiles and been quite pleased with the results.
But today I've had three crack on use although they were printed a week ago and have been handled since.
Any ideas on what I might have been doing or is it likely to be just applying too much pressure when printing?

[Paul]

They may be to cold when you press them. Or do you cool them by dunking in water?

[ScotTs]

heat them up for about 15 secs before pressing and leave to cool naturally.