Cracking is usually caused by quick cooling. Did you crack the top of your kiln open with a stilt and let it cool down slowly?
> I just did a glaze firing and I experienced a tile project that cracked and
> one that broke in half. I have the option on my kiln to do a fast glaze - 5
> hours or a slow glaze cycle - about 7 hours. My thought is that the
> fast glaze heated up to fast and caused the cracking. Does anyone have some
> thoughts of why this happened?