I was told old glass windows were thicker on the bottom because of how the glass was made. A big bubble of glass was blown, opened at the bottom and spun flat, resulting in a big pancake of glass with thick edges and a punt in the center. Rectangles were then cut from this. Another version was that a glass cylinder was blown, the top and bottom removed, a slit cut down the side and the glass flattened while it was still warm. Regardless of the manufacturing method, if the glass was thicker on one edge, the glazier would install that edge on the bottom so water flowing down the glass would be directed toward the outside of the building.
Dragging the thread back on track, when I was in college I made some microtome knives for a biology lab I was in. The process involved breaking a piece of 1/4" thick glass about 2" square across the diagonal. The cutting edge was the tip of the 45 degree corner. You had to inspect the edge with a magnifing glass because even if you broke it correctly, only about 2/3 of the edge was sharp enough to be usefull. The smoothness of the edge was important otherwise "grooves" would be left in the specimen slices.
Dragging the thread back on track, when I was in college I made some microtome knives for a biology lab I was in. The process involved breaking a piece of 1/4" thick glass about 2" square across the diagonal. The cutting edge was the tip of the 45 degree corner. You had to inspect the edge with a magnifing glass because even if you broke it correctly, only about 2/3 of the edge was sharp enough to be usefull. The smoothness of the edge was important otherwise "grooves" would be left in the specimen slices.