Plate Glass was the original method of producing completely flat glass for windows and mirrors. The method consisted of pouring molten glass onto flat metal tables and rolling it flat before cooling.
Plate glass was initially created in France in the 17th century. The manufacturing went through a number of improvements and until it got to the buicheroux process, which was developed in Germany in the 1920s where a tonne of glass is melted in a pot and hauled to the table, where it gets poured through a pair of rollers.
The quantity of grinding required for flatness was lowered by rolling the sheet.
Plate glass was commonly used for windows, doors and storefronts until the 1950’s when the float process was invented. In modern times, a lot of people still refer to ordinary annealed glass as plate glass when it was actually manufactured using the float process.