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The History of Double Glazing
Sourced from American articles on American Solar Passive housing in the 1950’s American mass-produced double glazing become a crucial component in the design of efficient housing from that point forward. It is not widely known that the “double glazed” window had been patented 154 years ago but did not become popular until the Americans commercialised the product in the mid -20th century. As manufacturers of double glazing at Climateframe Double Glazing we believe that to know where we are going then it is very important to know where we are coming from. Therefore, we feel it is important to provide a brief overview of the technology prior to discussing its development as a efficiency necessity in the 20th century.
Glass was originally made out of volcanic obsidian which was used in decorative pieces and ceremonial weaponry, this can be traced back to as far back as 5,000 BC by the Phoenicians, man made glass would not find any true use until the development of “blown” glass discovered as a technique by the Syrians glass makers of the first century AD, this then led to Romans being the very first to adopt glass for window technology. They came across the technology by way of conquest, which is widely documented by many historians and details of which can be easily found from other sources.
Romans made their glass windows with glass that was blown, spun and then cut into a flattened disc. The next step of the process was to lay the newly blown glass onto an iron tray and then cut into small plates. These small plates could then be utilised as windows by the Romans to essentially retain heat (how similar to our requirements for double glazing today). Glass was extremely expensive to produce because early crown glass was often uneven and unclear due to glass cooling too quickly for the plate to be flattened. This led to an additional process of grinding and polishing the glass to provide greater transparency.
Clear polished glass came to Europe in the 16th Century by the migration of Venetian glass makers to northern Europe in the late 15th century. This clear polished plate was a refined clearer product than its predecessors. 1674 leaded glass was developed in England making glass easier to work with and flatten for longer periods, the Crown’s policy of “daylight robbery” from 1695 to 1851 reduced the application of glass in windows and probably significantly set back the technology during this period. It wasn’t until 1834 with the emergence of cylinder sheets which allowed for production costs to be reduced and larger panes and therefore larger windows to be produced. It wasn’t until tax was cut later that resulted in a boom for the glazing industry afterwards.
“Double Glazing” itself was patented in 1865 by Stetson via a sash window system, this was designed to work around thermal loss and acoustic transfer. The patent details a clever construction of timber spacer bar separating two sheets of glass by a gap this was adhered via a putty made of whiting and oil. This putty increased production time due to it taking a couple of weeks to harden properly prior to shipping.
It may have been the costs, as mentioned above that meant double glazing was not greater in its popularity at the time of the original patent, or it may have just been a simple case of too much technology too soon.
It was realised during this time that there would be expansion and contraction due to changes in thermal conditions between the interior and exterior glass sheets. This caused stress on the inner components which broke the bonds with the sealing coat. It was favoured to dehydrate the air rather than fill it with gas (we fill the cavity with argon gas today) to avoid product failure. This design became very successfully throughout the 1950’s and 1960’s all throughout the United States of America.
In the early 1930’s it was recorded that only 10% of homes in the United Kingdom had double glazing prior to the oil crisis in 1973. Pilkington developed float glass in 1957, this was formed on a molten layer of tin which flattened under its own weight eliminating the production process of polishing, this reduced cost (which was a huge prohibitor at the time). During the crisis there were efficiency limits on windows, and this combined with Pilkington’s invention allowed demand for double glazing to flourish in the UK.
In the 1970’s it was discovered that the early aluminium double glazing experienced condensation rotting out the timber sill underneath. Aluminium framed double glazing was widely replaced with UPVC by the 1980’s and now represents 50% of the double-glazed market. Wood and aluminium have 25% market share each. And this remains true for the most part right to this day.
