Sometimes a glass window can have marks that may initially look like dirty, but are not. These are often due to chemicals that have bonded with, or reacted with the silica in the glass, or even with the thin layer of tin that remains on float glass [1].

These may be from a variety of sources, the most common being:

  • Clouding from hard water.
  • Clouding from chemicals/mineral leaching from the concrete surround.
  • Windows in direct line of a boiler flu.
  • Windows not cleaned for a very long time (usually years since the last clean).
  • Silicon sealant left on the glass (often from the installation of the window). This can be a blob or very fine layer of sealant.
  • Rust on the glass – often because of very small pieces of ferrous[2] metals that have gotten embedded, or stuck to the glass for a long time, then rusted.
  • Discolouration in small patches or spots. Often from cement splatter that has stuck to the windows during building work, then left on the glass. The concrete reacts with the glass over time, and can cause discolouration where it is in contact with the glass.


Some of these issues can be corrected with treatments to restore the glass either fully or to greatly improve it. I can perform these different treatments if requested. Prices vary, though often the average household window will cost about £10 to restore. If the restoration process doesn’t work – you don’t pay. I will only restore the glass at your request / permission and will not do it without your prior approval.

It is difficult to show pictures of worth that has been done, as most attempts by me to photograph the glass doesn’t come out well. Though here are a few examples photographed as best I could:



Discoloured Glass Window This window has been discolored from two main sources. It hasn’t been cleaned for a very long time, and it was near the flu exit of a boiler. No amount of normal cleaning was going to make any impact on this. The glass surface was no longer glossy, but now matt and rough with chemical damage. The photograph here was taken ‘after’ the window was thoroughly washed and scraped with a very sharp specialist window cleaner’s glass scraper!
 Top Window Now Treated  This is the same window as above. The top piece of glass has now been treated. You can see that it is now clear like a normal window. The glass below is in the process of being restored. You can see some of the bonded layer has been removed.



Silicone Sealant on Glass WIndow There is a mess of silicone sealant along the bottom of this pane of glass. It was probably done when the glass was fitted, as the sealant was used to seal in the glass pane. But it was not cleaned up afterwards. This silicone has been on the windows for a number of years now.
Silicone Sealant Removed From Glass Window The sealant has now been removed from the glass, and it looks much better. Special chemicals and tools were used to remove this, and great care was taken to leave the actual glass seal untouched.



Discoloured Pained Metal Wndow Frame This is a very discoloured painted metal window frame. This was near a boiler flu outlet and not touched for years. Specialist acids were required to strip the discolouration, yet leave the paint work intact. You can see the process is still taking place, the left has been cleaned, the right is still to be treated. The whole frame has already been cleaned with conventional cleaning materials.



During Glass Treatment of Hard Water Damage The glass on this window had been damaged with hard water. You can see that I am in the middle of treating it. There is a vertical area down the middle of the glass which is now clear as I restore it.


These are just a few examples as taking pictures of glass damage is actully tricky – well, I find it difficult as I am not a photographer. So, I have only a few pictures that I can use.




[1] – Float Glass is the common process for producing sheet glass used in normal windows. See this wikipedia article on float glass for more information.

[2] Ferrous Metal is a metal that contains iron in it’s mix. Iron is the part of metal that rusts, which is why some metals rust and others don’t. Here is an article from Castle Metals on non-ferrous and ferrous metals.

Treatment of Discoloured Glass Windows