`Jenna Germany historical window`

200-year-old plate glass window with visible chemical-inhomogeneity distortion; modern replacement pane (float glass) in same frame shows undistorted reflection. Used to illustrate pre-stirring vs post-stirring glass quality.

If you want to see a picture, probably from the 19th century — here's a picture of making plate glass. You start with a metal table — slightly inclined, that was an invention in the 1800s, to use an inclined table — and here's your steel roll, and they take this molten stuff and roll it out flat. The problem is, there are inhomogeneities in the glass, and that type of plate glass, unless you ground it and polished it, and even then, still had a lot of distortion. This is an old window in Jena, Germany. Here's a piece of modern glass — which is not plate glass, it's actually what we call float glass, I'm going to talk about that — and you can see the reflection of a tree in that glass. Here is some of the old plate glass in the rest of this window, and you can sort of see the black outlines of the tree, but it's been distorted. Someone broke the glass up here and they had to replace it.

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