One of the things you learn very quickly when working with recycled materials is to never expect the same result twice. This can be a great thing from an artistic standpoint, because you really learn to roll with it rather than get all wound up in it.
This became obvious as I was getting wildly differing results from different windows using the same techniques.
After spending a lot of time researching window glass, I discovered that the glass manufacturing technique has a huge impact on the final results. Also, if you can ferret out what the method was, you can use these idiosyncrasies to your advantage.
I made four seemingly identical plates with different kinds of window glass to show you what I mean. There will be additional posts in the near future exploring each different kind in greater detail and showing how to use the different characteristics in your design work. I’ve included a greatly simplified explanation of how each manufacturing process works.
1/4″ plate glass. Plate glass is a manufacturing technique that fell between drawing glass and float glass. The glass was poured and then machine polished on both sides. This gave a spectacularly clear optical class. Plate glass is typically a bit thicker than float glass and has a more green or yellow tint. At slumping temperatures, it maintains clarity, at fusing temperatures, it clouds and can wrinkle on the edges.
Right hand side:
1/4″ Float Glass. Float glass is the most current glass making technology. Molten glass is poured over a molten tin bath, giving a very clear smooth finish with a thin tin coating on one side. The tin side can be detected with a black light. Float glass typically slumps and fuses very smoothly, with a nice edge and very clear.
1/4″ Textured Plate Glass. This glass was rolled or poured over a textured plate and then the back was polished. The texture will remain at slumping temperatures, although it does still have a tendency to cloud or frost. Fusing temperatures will cause the texture to melt out.
Left hand side:
2 layers single strength sheet glass. Drawn glass is a manufacturing technique where a bar was dipped into a molten glass bath and drawn upward, bringing the glass with it in a thin sheet. Most of the glass that I get made with this technique comes from houses built prior to 1910. This is the glass that has a “wavy” look to it, and changes thickness across the sheet. This glass will keep it’s clarity at slumping temperatures, but will wrinkle badly at fusing temperatures. In addition, the layers don’t completely fuse together and often remain visible even at full fuse.
If you are really interested in glass manufacturing processes, I highly recommend acquiring a copy of Fay Tooley’s “The Handbook of Glass Manufacturing”.