And then calcium, and its revelation, I'm persuaded, of a medieval knowledge of materials and what they can give. Alabaster, a.k.a gypsum, is a combination of calcium, sulfur, oxygen, and water: thus the beautiful hieroglyph: CaSO42H2 (dang, can't do subscripts here, that's where you'd put the numbers). Lots of calcium there. What I need to ask my colleagues is whether or not calcium is "responsible" in some way for the porosity. For guess where else calcium shows up in huge amounts? Ivory. Calcium phosphate to some. Favorite medieval carving material to others. Hardness level? 2. This calcium commonality may be a bigger whoop for us moderns, because it likens two separate disciplines - we realized we needed a vertebrate biologist at the table when ivory emerged. A medieval sculptor existing within no such disciplinary divides could desire both equally for their give to touch, pigment, and gold. I'll confess that it's the presence of calcium in the human body, too, that thrills me here. A chemical commonality that reformulates these works of art as material extensions of the human. Or human participation in their materiality. Scientific facts, medieval practices, modern desires - let's see how this goes.