Float Glass

Approximately 90% of the world's flat glass is manufactured using the float glass process, a technique developed in the 1950s by Sir Alastair Pilkington. In this method, molten glass is poured onto a molten tin bath at one end, where it floats, levels out, and forms smooth surfaces on both sides as it spreads along the bath. As the glass cools and solidifies while moving over the molten tin, it transitions into a continuous ribbon and is then annealed in a cooling oven known as a lehr. This results in glass with nearly perfect parallel surfaces.

During this process, a very small amount of tin becomes embedded on the side of the glass that contacts the tin, making this side preferable for creating mirrors due to its ease of treatment. This characteristic facilitated the transition from plate glass to float glass. Additionally, the tin side is softer and more susceptible to scratches. The glass is available in standard metric thicknesses such as 2, 3, 4, 5, 6, 8, 10, 12, 15, 19, and 22 mm.

The molten glass, when floating in a nitrogen/hydrogen atmosphere on the tin, naturally spreads to a thickness of about 6 mm. Adjustments for thinner or thicker glass involve stretching the glass or restricting its expansion as it cools, respectively.