I think using cullet made from window glass as a a frit in a glaze is one of those things that is possible in a realm of infinite possibilities, but could be more trouble than it’s worth if you’re trying to build a glaze for functional use. Since the OP is referencing a mug, that’s what I’m assuming we’re after. Float (window) glass has less alumina and silica than bottle glass does, and contains lots of sodium from a couple of sources which are germane for refining bubbles out, but not ceramic purposes. It’s also got lime, so some calcium and magnesium. There’s no boron in it, so I’m not sure how it’d act as a borosilicate frit. (For borosilicate, you’d need older Pyrex, or lab glass). You’d have to do a lot of testing to fine tune window glass cullet in a recipe, given you don’t know the exact proportions of the materials used. Plus, it’s a LOT of hot, sweaty work in a respirator to pound it into powder. The COE of window glass is approximately 8.4. Ceramic glazes tend to be somewhere in the 6-7 range, depending. If you’ve got chunks of glass in a glaze as in the picture the OP provided, they’re going to pull away from each other, creating stress fractures in the work. I bet that mug in the example picture weeps if they used window or bottle glass. Or even some of the colouring stuff sold for use in a glassblowing studio.
If we’re talking about a sculptural effect, go right ahead and do whatever wild and whacky thing that makes your experiment hungry heart happy. Science is cool.
