Online coatings are applied directly to glass during production, before the glass has cooled. The coating is applied by vaporising a chemical compound over the semi-molten glass.
The online process, known as CVD (Chemical Vapour Deposition) is the more traditional form of applying coatings but the process cannot be used for applying all types of compounds. Another problem with the traditional form of online coating is that it cannot be applied with the same precision possible in the latest offline processes. The metallic layers in online coated glass are therefore thicker which gives the finished glass a slight tint - making white curtains, or white Georgian bars, appear grey.
The online coating process can also cause small indentations on the surface of the glass before it sets, which gives doucle glazing window a ‘hazy’ or dusty looking appearance.
Online coatings are, however, highly durable and especially suitable for use where coatings are positioned on face 1 (the exterior facing outside pane) – such as for self-cleaning glass.