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What difference would it have made to our species鈥� technological development if glass wasn鈥檛 transparent?
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Pat French
Longdon-upon-Tern, Shropshire, UK
As with any major innovation of long standing, we must assume that, in the absence of transparent glass, other avenues would have been explored to a similar degree for the various industries that employ glass today. Animal horn, hide, various crystals, paper and ice are materials that have been used where window glass was not available, and technologies might well have developed around these substances. Once transparent plastics started to become available, presumably much of today鈥檚 technology would have followed or already been bypassed. Were the same resources invested in natural materials as have been allocated to glass and other ceramic research, who knows what might have emerged by now. One can imagine organic and crystal alternatives to glass lenses and fibre optics.
Opaque glass could still fulfil many of the functions of clear glass, if not always so conveniently. Presumably, it would still be possible to mould and blow opaque glass and it would still have its insulating properties. But gothic horror films would be very different without coloured liquids seen bubbling in flasks.
Alex McDowell
London, UK
In a universe with no transparent material, lenses wouldn鈥檛 be possible, and cameras would have to be of the pinhole type. Instead of corrective lenses, one could use 鈥減inhole glasses鈥� with lots of small holes in them.
The use of glass also revolutionised chemistry: chemists could use small amounts of reagents and see colour changes in test tubes. Before the advent of glass, they had to use cauldrons and large amounts of chemicals so that they could see colour changes. Glass has the advantage of being inert, but so do some metals, including gold and platinum.
Sam Edge
Ringwood, Hampshire, UK
Glass is used for many other reasons than its transparency. Some of its other useful properties are hardness and non-porosity when cold, ductility when hot, heat resistance, lack of chemical reactivity, longevity and surface smoothness.
These have led to its use for storage of things that must be kept clean and, in some cases, dry and even hermetically sealed. For this, transparency is sometimes convenient but not vital. Indeed, much glass used this way is merely translucent or even opaque to protect the contents from light damage. These properties also led to its use scientifically and industrially. While performing a laboratory titration might be tricky with a non-transparent burette or flask, heating a test tube over a Bunsen burner doesn鈥檛 really require transparency.
The use of glass also revolutionised chemistry: chemists could now see colour changes in test tubes
Before the modern float glass process was developed, a lot of glass used for windows was less than fully transparent. Window glass is mostly there to allow natural light in and to keep the weather out without degrading. Windows as viewports to the outside are nice but not essential in most cases. Many other materials are translucent enough for this purpose. Paper was used for internal walls in many places, such as Japan, to provide privacy while still allowing light through. Paper can be waterproofed without becoming opaque, so it could be used for external windows as well, even in wet climates. Igloos are sometimes fitted with a window of thin, smooth ice that has formed on a water surface.
There are other naturally occurring and synthetic translucent and transparent materials, such as some plant fibres and thinly sliced woods, crystals such as quartz, polymers like Perspex and so on. Without glass, I imagine these would have been pressed into service, and their use refined. Without transparent glass, other solutions may have been discovered by necessity.
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