What if glass had never been invented?
Imagine waking in a world where glass had not been invented. All glass utensils have vanished we cannot have clocks or watches because they cannot exist without the protective facing of glass. We can’t have light bulbs without glass, we can’t have windows without glass: if we suffer from short or long sight there are no contact lenses or spectacles to help us. There is no mirror in the bathroom to shave with, no bottles or jars for ointment, no glass for your toothbrush. There is no television in the living room – without a screen, they cannot exist. When we look out of the window we see no cars, buses, trains, or airplanes for without windshields none of them can operate. The shops in town have no window displays and our gardens have no glasshouses. Our understanding of astronomy and biology would be very limited because there would be no telescopes and no microscopes. It is hard to conceive of the scientific revolution without barometers, thermometers, vacuum flasks, retorts, and a whole panoply of other glass instruments. The artistic and aesthetic world would be entirely different there would be no photographs no films no television no Gothic cathedral windows and no stained glass masterpieces by Louise Comfort Tiffany, John La Farge, or Frank Lloyd Wright.
Samuel Johnson Muses About Glass
“Who when he first saw the sand and ashes by a casual intenseness of each melted into a crystalline form, rugged with excrescences and clouded with impurities, would have imagined that in this shapeless lump lay concealed so many conveniences of life as would in time constitute a great part of the happiness of the world. Yet by some such fortune which is liquefaction was mankind taught to procure a body at once in a high degree solid and transparent which might admit the light of the sun, and exclude the violence of the wind; which might extend the site of the philosopher to new ranges of existence, and Charm him at one time with the unbounded extent of material creation and at another with the endless subordination of animal life; and, what is of yet more importance, might supply the decays of nature and succor old age with subsidiaries sight. Thus was the first artificer in glass employed, go without his knowledge or expectation. He was facilitating and prolonging the enjoyment of light, and enlarging the avenues of science, and conferring the highest and most lasting pleasures; he was enabling the student to contemplate nature, and the beauty to behold herself. “
Dr. Samuel Johnson 1750.
The nature of glass – a super-cooled fluid
The material glass is not as simple as it looks. Although it is rigid and therefore acts like a solid, the internal molecular structure is disordered and random – more like a liquid. This is unlike the ordered arrangement of atoms and molecules in metals and crystals.
In molten glass the atoms of silicon and oxygen are tied together so loosely as to make the glass transparent. This disarray takes place during the melting process and before the atoms can reorganize themselves into regular patterns, the glass is cooled and all movement stops – producing a kind of frozen relict of liquid glass.
The very randomness of the molecular structure gives glass what technicians refer to as its formability – the ability to be made into thick flat sheets strong enough to stop a bullet and into very fine fibers capable of being woven into flexible objects or able to transmit light in fiber-optic cables. There is glass finer than a human hair, thick glass for transparent staircases, colored glass for stained glass windows, heat resistant pyrex for cooking: there is ground glass, cut glass, frosted glass, and milled glass.
Ductility of glass: an urban legend
The fact that glass is a type of super-cooled liquid lead some observers to speculate that glass could continue to flow, albeit very slowly, over historical time periods of centuries or millennia. Close examination of the small pieces of colored glass in the great Medieval Cathedrals of Europe showed that many were slightly thicker at the base and thinner at the top. Since some of this glass is almost 1000 years old, it was speculated that very slow viscous flow, under the force of gravity, had caused this thickening.
This theory has subsequently been shown to be false: theoretical calculations show that glass is much too rigid to be deformed at atmospheric temperatures and systematic, detailed measurements show statistically that many of the glass lites are thicker at the top. It was a fun theory while it lasted!
Is a broken mirror 7 years’ bad luck?
The famous superstition that a broken mirror means 7 years of bad luck is believed to date back to the Romans who believed than periods of bad health tended to occur after a seven year period. They therefore felt that after 7 years the average person would be ready for a bout of sickness, heart problems, biliousness and disease and that this was announced by the cracking of a mirror. A better explanation is that mirrors were extremely expensive back then and the curse was a threat made to slaves and servants to make sure they took great care of the precious mirrors.
In any case, a broken mirror had the same status as a black cat in ancient folklore and even Tennyson was aware of the danger – as he explained in these immortal lines spoken by the fabled Lady of Shalott:
She left the web, she left the loom,
She made three paces thro’ the room,
She saw the water-lily bloom,
She saw the helmet and the plume,
She looked down to Camelot.
Out flew the web and floated wide;
The mirror crack’d from side to side,
“The curse is come upon me,” cried
The Lady of Shalott.