Sometimes, there can be a sort of hazy look to windows if you catch the light at the right angle. It almost looks like there is something on the glass, or maybe it has some sort of residue from the window cleaner? Well. glass is clear right, so of it looks like there is a distortion right over the pane, it means something has been done badly by the window cleaner – right?

Sorry – wrong.

Architectural glass today is more complicated than you may think. Various things can affect the look of the glass and the article below explains why this can sometimes happen – and it’s not the window cleaner’s fault 🙂 The article is by Pilkington, a wold leader in glass manufacture and the main glass manufacturer for household window panes in this part of the world.



Why have I got a haze/milky appearance on my windows?

Haze is an optical phenomenon which makes the glass look like it is covered in a very fine, uniform layer of dust when viewed from an oblique angle or viewed under strong light incident on the glass at an oblique angle. Our original Pilkington K Glass™ can, under certain lighting conditions, display this phenomenon to a limited extent.

The reason for this is that the Pilkington K Glass™ coating is not as smooth as the glass surface. While this is not obvious to the eye when examining the glass, some people who regularly handle Pilkington K Glass™ can tell which side the coating is on by the feel of it.

The optical effect of the slightly rougher surface is to scatter a small proportion of the light incident on it (in exactly the same way as a thin layer of dust would, which is why it looks similar).  With Pilkington K Glass™ the amount of scattered light is generally less than half of one percent of the light coming through the window, so under most viewing conditions it is not obvious. However, when incident sunlight is at an oblique angle and the view through the glass is of a shaded area, then the scattered light can become more visible, giving rise to the appearance of haze.

Nowadays low-emissivity glass is coated using alternative technologies so that our latest low-emissivity glass products; Pilkington K Glass™ S and Pilkington Optitherm™ do not suffer from this phenomenon to such a noticeable degree.

Article Copyright © Pilkington Glass

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