We've all seen art, or obscure glass, even if only in those security panes set in the doors of public buildings we've been in.
Modern windows actually began with this type of glass. The first Roman windows were a matrix of glass pebbles set into a frame. During the middle ages, French glassblowers found a way to spin a hollow bubble of molten glass into a flat circle. The circles were assembled in frames to create a window. The shape that took advantage of these discs with the least waste was the diamond, which is why the diamond shape is still often seen in leaded glass windows.
Also called French Embossing, etching glass involved the use of wax to isolate areas of the glass from an acid bath that etched the remainder of the pane, making it non-transparent. Acid etching was created in the late 1800's, as a way of using glass to enrich and enclose private spaces, and is still used today, although it has been replaced, for many purposes, by the less expensive technique of sandblasting.