I have done a flip and fire and gotten rid of smaller bubbles. Doesn’t always work but worth a try.
I flip and fire
if the bubbles go away ..I fire again on the design side to get the glossy look.
I did accent tiles for my kitchen backsplash. I went and got the size of the plain tile from Lowes that I wanted to use and that is the size tile I made.
Mine are two layers thick. There may be a little difference in thickness but the grout lines hide that. They stay square as long as you don’t over fire them.