Hello. Thanks for the useful advice. Frost would to my opinion only be detrimental if they would hold the water and freeze. Since this is not the case (as you mentioned) I don't see a problem but I'll check it out my self next winter.
Kris

Hi Kris,

Sorry, did not see any mentioning of the clay being fired hot enough to no longer absorb water!

You're right. There fired at 1050°c. The temperature for Raku.
It means that the inside (not glazed) will absorb some water.
If they need to be used outside in winter, a thin indelible transparent coating would solve that problem.
Kris