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The Short History of Glass
How Glass is Made
1: Acquire silica sand.
Also known as quartz sand, silica sand(SiO2) is exactly what it sounds like: sand. You can go to the beach and grab a bag of it yourself, but it would be chock-full of impurities.
2: Add sodium carbonate and calcium dioxide.
Sodium carbonate lowers the temperature required to make glass. Why is this necessary? It makes is so that glass can be made commercially (in other words it lowers the cost of making glass). However, adding sodium carbonate has negative consequences; it allows water to pass through glass. Therefore, calcium dioxide is added to negate this property.
3: Add chemicals for the intended purpose of the glass you are making.
Glass is used for many different purposes today, from bulletproof glass, to bottles, etc, and each type of glass has its own chemical composition. In this stage, various chemicals are added for the intended purpose of the glass being manufactured. For example, lead oxide is added to make crystal glass, or to make the glass sparkle for decorative purposes. Lanthanum oxide is added to eye glasses because of its refractive properties.
4: Add chemicals to produce a desired color in the finished glass product
Various chemicals can be added for different colors. Iron oxides or copper oxides turn the glass green. Gold chloride turns the glass red. The addition of nickel can turn glass blue. So on and so forth.
5: The desired mixture is then placed into a heat resistant holder (such as a crucible) and melted in a furnace.
6: The mixture must be homogenized and the bubbles removed by stirring and adding other chemicals.
Homogenize simply means to make the now molten material uniform throughout, which can be done by stirring or adding chemicals. The same is true for getting rid of the bubbles.
7: Shape the molten glass and let glass cool.
There are many different ways to shape molten glass and an indefinite amount of things you can make glass into. Corning Glass Museum can show you more.
8: Anneal the glass, or temper it, for strength.
Annealing is basically heating the product beyond the critical point (the point at which no phase boundaries exist) and letting it sit at that temperature before gradually (or quickly) cooling the temperature down.
The Discovery of Glass and its Early Beginnings
No one knows for sure exactly when glass was discovered. Over time the origins of glass making have been lost to modern society. There is a historical account that suggests glass may have accidentally been discovered by Phoenician merchants, while others argue whether or not it began in the Stone Age (approx. 5000 BC) or the Bronze Age (approx. 3000 B). Most researchers, however, seem to agree that glass was first made by humans somewhere between 3000 and 2000 BC during the illustrious Bronze Age.
Glass making was believed to have begun in Mesopotamia, the cradle of society, where small objects were created by casting the glass in molds or shaping with simple tools. Though it cannot be known for sure, the art of making glass is believed to have been accidentally discovered while making bronze and other metals. Researchers came to this conclusions because the earliest known surviving examples of glass are small beads believed to be byproducts of metal work.
From there the art of glass making began. The original process was long, labor-intensive and laborious and often involved core forming. How core forming worked is still highly contested among archaeologists, but the basic concept is that glass was added to a core (a certain mold of various shapes) either by dipping or application with tools and then decorative pieces were pressed on. Everything was done by hand with delicate care, the process not only long, but expensive. Therefore, only the very wealthy could afford to buy anything made of glass and glass products were made specifically for the wealthy. Vessels to hold perfume or makeup (luxuries not afforded to the poor at the time) were created as well as intricate decorative pieces, such as glass busts of the pharaohs. Surely not something the average proletariat could ever hope to own.
For centuries little advances were made to the technique of making glass. It was until approximately 50 BC, in the Roman Empire just before the height of Ceaser’s rule, that a new and quicker way of creating glass was discovered, making it available for ordinary household use. While lavish and luxurious glass was still constructed with the utmost care and with intricate details and shapes, with the new technique everyone could own a piece of glass. This technique discovered was called glass blowing, still in use today. I won’t go into detail about glass blowing, but I did provide a video from Corning Museum on how glass blowing is done. The video is a little on the boring side, but I found it to be more informative than the others and of better quality. With this new technique glass could be made not only cheaper and quicker, but into a wider variety of shapes and for a greater number of purposes, such as candlesticks, ewers, vases, drinking horns, etc. No longer was it a material simply for the wealthy.
Glassblowing by Corning Museum of Glass
In modern times, limestone is often the source of calcium dioxide and soda ash is often the source of sodium carbonate. Recycled glass pieces can also be added to the mixture.The ancient Romans used calcium rich sand and mineral natron to make glass. The Muslims changed the recipe, using pant ash as the source of sodium carbonate instead of natron, which historians believe is because they did not have access to mineral natron.
Glass in Ancient Asia and Middle East
While glass thrived in Europe and later America, glass had a late start in Asia, especially China. Imported glass reached China long before the Silk Road was established, mostly in the form of glass eye beads, creating a demand for locally developed products. Early glass in China was made much the same ways as early glass in Europe, but with a vastly different chemical composition. The glass made was restricted to the wealthy as well, and consisted mainly as a cheaper alternative to jade objects, burial plaques and vessels mainly created for the wealthy.
After the collapse of the Roman empire in 476 AD, the art of glass making essentially disappeared. Little survived into the Middle Ages and the techniques still used were unsophisticated. It wasn’t until the 7th century, when Muslims began to conquer land and spread west, that Islamic glassmakers began to revive Roman techniques and develop new forms, such as glass cutting, mold blowing and lustre painting (adding a metal sheen to the glass vessel). Glass makers in the Islamic empire (modern day Turkey, Egypt, Iran, Syria, Israel, Lebanon, Persia etc) continued to revive and improve upon Roman techniques from the 7th to the 12th century.
The 12th century saw much turbulence in this area, however. The empire was fractured and punctuated by crusade wars with their European counterparts. Glass making in certain parts of the area stopped altogether for reasons unknown today. However, in Syria and Egypt glass making began to flourish. Finished glass products became an art form and various decorative traditions began in this time to accomplish such feats. Techniques such as marvering (a hard, flat surface of stone, wood, or metal, on which a mass of molten glass is rolled and shaped in glassmaking), enamelling, and gilding (essentially covering a glass piece in gold) were developed to create artistic pieces. To make glass in this area required both artistic creativity and a strong technical sophistication.
Glass During the Renaissance
But we’re not done yet. What was happening in Europe during all of this? Why the Renaissance of course. We’ve all heard of the Renaissance and maybe a few of you have had a small taste of what it might have been like at a Renaissance fair. The Renaissance was a widespread cultural movement that affected most of Europe from the 14th to 17th century. During the Renaissance intellect flourished as the Middle Ages faded away. Great changes and discoveries in science were made, politics changed, diplomacy was created, art began to take on a new form as creativity began to spread and as knowledge began to grow. The way we looked at the world changed. Glass making thrived with new technological advances. Lead, they found, when added to a glass mixture made the glass sparkle and gold chloride could turn the glass red. The designs were greater and more detailed and luxury glass making flourished. Entire paintings could be done on a glass, tiny details could be engraved into beakers and glasses and while more ordinary designs were still created for the masses, the lavish designs created for the wealthy had no limits.
By the 18th century, the Renaissance was over and many of the more lavish and ornate styles of making glass fell by the waste side. Stained glass, for example, was neglected. By the time the French Revolution came around, stained glass was being systematically destroyed or replaced. Very little remains from the Middle Ages or the Renaissance period. It wasn’t until the 19th century that stained glass was to be rediscovered. However, in the 18th and 19th century another form of glass making would come about. It was less a form of art, and more a commercialization.
Glass in Early America
The 18th century saw the birth of industrialization. Ever read the book The Jungle by Upton Sinclair? I have and it is disturbing. The Jungle is an accurate portrayal of industrialization and the fate of thousands of immigrants to the United States in the 18th century. As you can imagine, it is not pretty. Glass making, just like everything else, fell prey to industrialization. Consumers in America and Europe were increasingly demanding elegant glassware and soon glassware was mass produced for the needy masses. By the 1950s, the use of glass, thanks to industrialization, had spread from hand crafted art and elegant glassware to everyday use for everyday products, such as glass containers for Clorox bleach, soda bottles, beer bottles, candle holders, cups, plates, etc.
Corning Museum of Glass Demonstrations
Where to Learn More
There is so much more I didn’t include, but if you are interested in learning more yourself, I suggest you start with Corning Glass Museum’s website. The video on the right is a glassmaking demonstration from artists at the Corning Museum of Glass. I’ve wenter there once when I was a child and it was pretty awesome. You can also watch demos of glass making they do for live audiences at their website: http://www.cmog.org/glassmaking/demos.