A close friend went to a large academic library for a lecture, and very kindly had them pull a rare glass book for me. Inside was an essay on silver stain, about 25 pages long. The library offers free scanning/emailing and photocopies of texts, so I now have the essay in PDF.
I've gone from 1 confirmed period recipe to 3 or 4. For some of these, I had the primary source but I didn't recognize the recipe because it referred to a stone we think of as blue. The ancients didn't. I had another primary source and couldn't find a recipe within it. After this new text detailed exactly where it should be, I found out my copy of the primary source is actually only the first quarter of the full text. There was also a recipe from a source I hadn't read before. I will have great fun trying all of them now!
I bought a hand foiling tool. I thought it would let me quickly and perfectly foil glass. I WAS WRONG, and while copper foil isn't period in the slightest, it's how most of us learn and what most of us do most of the time. I had been warned they were not that great, and I am now passing along the warning. I did modify the directions' procedure in a way that allows me to more easily load the foil, however it requires wasting about a foot of foil instead of the 4" or so normally called for. The design needs to have the stripping slot at the opposite end of the handle from where it is. Also, I haven't figured out how you can cleanly cut the foil without a third hand, and the crimping part of the tool leaves something to be desired. Foil by hand, it's easier.
And a completely modern piece...