Work continues on silver stain. It's been my primary focus for the past few weeks. Tonight, after my birthday dinner, I started grinding some brick dust to try as a binder:
A little research suggests that before the 14th century almost all brick was what we'd call terracotta. I bought a small terracotta pot, set it on a ledge, and aimed a laser pointer at it. Gravity and a cat with a hair trigger gave me shards to grind into my dust. For testing my various binders (What was mostly planned to be "part 1"), I've been using silver nitrate and each binder (1:6). For what I meant to be my compound tests ("part 2") I've been using gum arabic. I've found no indication that it is a period binder for this purpose, but I trust it not to fire onto the surface of the glass.
Copper Sulfate is supposed to give an amber color to the glass. It's proving difficult and I think I will have to try it at a higher temperature. Silver sulfate and silver nitrate are both working as expected. I've purchased some "name brand" red ochre to try again; the 'generic' stuff I used before appears to be way off and now the line between phases of my project is quite blurred.
I'm presently up to four binders, three of which are mentioned in the period formula, and four compounds, one of which is mentioned in the period formula. Once I have some confidence in the binders I will smash up the materials needed to actually try the period recipe.