A warm or wintry welcome to all of our double glazing friends. Warm if you're sat cosily behind a newly installed double glazed window and a wintry welcome if the wind's roaring through the sides of your single glazed window sashes. Thanks for coming to see us. We should now be familiar with the ways those early glass makers crafted the glass sheets and the reason why lead was introduced into the glass window. Then we move over to the insulated or double glazing unit. What a luxury! Thirty years ago most homes and new window installations had only single glazing. Cold, damp and condensation was something that everybody had to deal with. Early innovators of the double glazing system came up with an idea of installing a secondary panel of glass to the inside of the window. This system was encased in a plastic type of framing. Another version was also available in an aluminium frame. Some forms of secondary double glazing are still being installed today. In its day it was a pretty smart way of preventing the warm air coming into contact with the cold air on the outside and creating volumes of condensation. It also kept in the heat and made the home much warmer than if only single glazing had been used.

Then there was Royal Doultons version of today's sealed units, these were called glass to glass units. Two panes of 4mm glass with a 5mm cavity between them. The units were held together with some kind of glass roll over and a plug seal to keep the air within the unit. That's my best description of them and they didn't last that long anyway. They were not that popular, but I do remember replacing a few of them full of water and totally steamed up. I know you won't believe this, but we went to replace a broken down insulated glass unit, it was full of water and a dead fish was inside the cavity. No way! I am serious, but have no idea how it got there. Modern day insulated glass unit making is not that far away from the early methods. My favourite has to be spending hour's hand cleaning two pieces of 4mm glass, clipping them together, only to see a bunch of hand marks inside the glass unit. Then there was that extra special job of mixing up the sealant and trowling it into the areas next to the spacer bar, sometimes the spacer bar bent in the middle because you hadn't put enough clips on.

I miss those days, what a carry on. Before today's modern windows, most sealed units were installed into existing wood window frames. This method required the existing glass to be removed and then replaced with an insulated glass unit.

Two or three years down the road the units would fail and begin to fog up. Sealed Units into wood frames, narrow rebates and no spacers or drainage, what would we expect? Most installations were guaranteed to break down before the glazier closed the gates. Butyl putty was the must of the day, but what good that did I will never know? Then they figured out that drainage was needed. If a glass unit sits in a pool of water for long enough, it's going to break down or steam up, in fact there is a chance you may find a fish in it. Now we're making glass units with aluminium spacer bar, no corner keys, and with desiccant and sealant that have 20 year life expectancy. They are installed in to PVC windows and doors and they also have drainage. So we have advanced a little.