What is a window? Simply, it’s a hole in a wall to let light in (or an arrow out!). The drawback with just a hole is that it does not just let light in, it lets heat out, lets the weather in and may let unwanted visitors in. Early “windows” in the Bronze and Iron Ages countered these downsides by using wooden shutters and even scraped and stretched animal hides (similar to drum skins) which were dipped in oils to make them translucent and waterproof. The invention of glass took things a step further by providing a cover for windows which lets in light at the same time as keeping the elements out.

The use of glass for architectural purposes began at the end of the first century AD when the Romans discovered that adding manganese oxide to the mixture made clear glass, albeit with poor optics. This glass was only used in the most important buildings. The pane production method, which was basically casting, remained largely unchanged until the eleventh century, when two techniques were developed. Both of these involved blowing a ball of molten glass into a bubble. The bubble was then either, pierced and spun into a disc, or the bubble was swung to form a cylinder, which was then slit and laid out flat. The panes were then cut from the parts of the plate with the best thickness and clarity.

At the end of the seventeenth century the French developed a method of producing larger plates of higher clarity. This was achieved by pouring the molten glass onto a special table. The glass was then rolled flat and the surfaces ground with fine abrasive powder. It was not until the nineteenth century that glass production became mechanised and mass production began. The early twentieth century saw a number of advances in plate production. Two methods for continuous plate production were invented in Belgium around the time of the First World War. These involved drawing ribbons of molten glass from tanks. The later version then drew the ribbon through rollers to obtain a consistent thickness and finish. Further drawing processes were developed in America between the First and Second World Wars, but the next major leap was the invention of the float process in Britain in the 1950s. This is whereby molten glass is poured across the surface bath of molten tin. The glass spreads and flattens before being drawn off in a continuous ribbon. The process is able to produce very large panes of extremely good quality and remains largely unchanged to the present day.

The development of window glass production methods to produce larger, flatter pieces with better clarity has had an enormous influence on the design of windows through history. It is the limitation of the size of a windowpane that gives us leaded lights and astragal bars. It is curious that some modern, expensive, glass effects are actually recreations of what would have been seen as faults, or even waste, in old glass.

Early glass production techniques of casting, blowing and spinning were such that only small panes of consistent thickness and clarity could be produced. These then had to be joined together with lead strips to produce a reasonable area. As glass production technology developed, larger panes could be produced which gave rise to the window designs of the age using the maximum size of pane to give the clearest view.

The Romans in England 43 to 409 AD used small pieces of glass in windows.

The Dark Ages from 410 – 1065 AD do not provide much evidence of windows but there are Saxon churches from the period which utilised early glass technology.

1399  –  1484  AD,  the  Late  Middle  Ages,  introduced Perpendicular Gothic and the Baroque styles, both highly decorative and intricate styles. They are distinctive from earlier windows in the form of the arches at the top. Early gothic arches were ‘two centred’ tall arches whereas the later perpendicular form has a low ‘four centred’ arch.

1485 – 1602 AD, the Tudor Period, saw the extension of substantial building from the ecclesiastical/royal/military areas towards domestic buildings, examples of which still exist.

1603 – 1713, the Stuart Period, showed little architectural development and instead concentrated mainly on war. The Great Fire of London in 1666 necessitated large scale re-building and introduced the neo-Classical style, with for instance, Christopher Wren (St. Paul’s Cathedral).

As often said and as stated in our introduction “beauty is in the eye of the beholder” and no one can say whether an individuals choice of style is right or wrong. However, hopefully the information in this guide has demonstrated that by avoiding a few obvious pitfalls, and by following some well-researched principles of proportion, it is possible to satisfy the eye of most people.

The British Plastics Federation Windows Group has a wide range of standards and codes of practice to assist all those involved in PVC-U windows and doors. More information is available from  www.bpfwindowsgroup.com

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