What glazes did Sheier use?
Edwin and Mary Scheier created custom glazes for their pottery, and they might layer more than one glaze on a single piece; however, we are having trouble locating what those glazes were made of. Their use of glaze was often minimal and they would purposefully allow the texture of the clay beneath to show through.
What do the three faces represent?
I am not sure that the three faces represent anything necessarily but we do know that much of Edwin and Mary Scheier's work (they were married and both created pottery) showed people-within-people or figures in womb-like shapes. They often use symbols of birth and the cycles of life in their art. They were also inspired by Chinese art, I don't know enough about Chinese art and motifs to say for sure, but possibly this was something that comes out of that inspiration. And here's an interesting fact: they first worked together as puppeteers, before they began collaborating on pottery!