Float glass

[5] Modern windows are usually made from float glass,[6] though Corning Incorporated uses the overflow downdraw method.

If the glass could be set on a perfectly smooth, flat body, like the surface of an open pan of calm liquid, this would reduce costs considerably.

Between 1953 and 1957, at the Cowley Hill Works St Helens, Lancashire, Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers developed the first successful commercial application for forming a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity.

[15] The success of this process lay in the careful balance of the volume of glass fed onto the bath, where it was flattened by its own weight.

[16] Full scale profitable sales of float glass were first achieved in 1960, and in the 1960s the process was licensed throughout the world, replacing previous production methods.

The raw materials are mixed in a batch process, then fed together with a controlled proportion of cullet (waste glass) into a furnace, where it is heated to approximately 1,500 °C.

To prevent oxidation, the tin bath is provided with a positive pressure protective atmosphere of nitrogen and hydrogen.

Once off the bath, the glass sheet passes through a lehr kiln for approximately 100 m, where it is cooled gradually so that it anneals without strain and does not crack from the temperature change.

[20] Due to both its high quality with no additional polishing required[21] and its structural flexibility during production, it can easily be shaped and bent into a variety of forms while in a heated, syrupy state.