I'd like to see the citation on this one, too. Your definition of "canon" seems to involve a lot of house rules and imagination...
I have to wonder if your "canon" rules on glass are equally unsupported by anything other than an equally creative leap between two otherwise unconnected sections of the rules.
Page 51, Covenants. As I wrote in a previous post in this thread. But maybe I imagined it.......
Just read it. Non-sequiter. That refers to using Rego to force a piece of existing glass into a finished product. Creo can be used to simply create glass in perfect ideal form, no roll needed. And glass is simply sand, so it isn't that hard to do at all.
I think you're refering to the statement in covenants that Rego craft magic cannot produce CLEAR glass. This refered to CLEAR glass requiring an alchemical process.
"Glass" is not clear in its "perfect" form, apparently.
You certainly imagined exactly what it said, what it applied to, and what it meant re the rules as a whole. 
But that seems to be a pattern that's forming.
However, in your defense, I'll say that's not an uncommon or difficult mistake to make, quite the opposite, unfortunately. With all the rules and all the details within the rules, often one gets lumped together with others and somehow that "lump" becomes "canon" in one's memory. That's why I try (try) to re-read any section before I quote it - I often find my own memory (often surprisingly!) mistaken regarding the specific point at hand.
(And that's why my sig reads as it does - as a reminder to me as well as anyone else.) 
Hermetic magic clearly can make transparent glass without much problems. A little CrTe and there we go. In fact, several spells (like the one creating a perfect lab equipment) require it. Far from the most difficult thing to achieve with hermetic magic 
I would expect most covenants to have glass windows.
Cheers,
Xavi
(Not according to the passage in question. Ysmv.)
Didn't imagine it, it's just an obscure bit mentioned in one place. It stuck in my head because I haven't encountered anything else in canon when it comes to craft where it says clearly, you can't do this with magic. Magic doesn't have a problem with clear, you can CrTe perfect gemstones. So why is it possible to have clear, Diamond windows, but your CrTe glass windows will be bubbly and dull, letting through a little bit of light? Maybe "clear glass" hasn't been incorporated into Hermetic Magic by Vulgar Alchemy yet. Maybe the dull bubbly fragile rock is the Platonic Ideal. What ever the case, magic has a problem with glass, and only glass, as far as I can tell. So it's a bad idea (in my mind) to use it when trying to form a pattern.
Except your CrTe glass windows WONT be bubbly and dull. But your ReTe made windows WILL. You mix up Re and Cr completely.
Reread above posts.
Most specifically:
And: