Thank you for answering my inquiry. I am working with an artist that uses commercial tiles and has a formula for the grout. That is all figured out. I will be making hand made clay tiles to add to the mural. The thing I need to figure out is the clay and glaze. I would like to use Laguna #66 and amaco celadons or HF glaze. How do you know if the clay is fully vitrified and that the glaze fits?