I wrote the following essay as a freshman after taking a glass blowing course. It was a very inspiring afternoon and afterward I wanted to learn more about the history of the material.
Alchemy of glass
Shockingly intense light and heat poured from beyond the door. Hands of flame leapt from the white-hot inferno, and the skin on the left side of my face felt like it was about to be set ablaze. Then the man closed the furnace door and the white-hot light dimmed. I was in the Diablo Glass School in Boston, and had just dipped the end of my glass working tube in to a two-foot diameter crucible full of molten glass heated to two thousand degrees Fahrenheit. The experience of glass making would cause anyone to wonder about the magic of glass and its fascinating combination of history, art and science.
Imagine a place where the conditions in the furnace at Diablo’s School happen in nature. For millions of years these volcanic environments have created a naturally occurring glass called “obsidian”. Obsidian is fluid lava that cools so quickly that it doesn’t have a chance to form into the crystal structure of a specific mineral. All rocks consist of mixtures of various crystalline minerals. When crystallization occurs, the atoms arrange in regular, geometric patterns. Obsidian consists of about 70 percent or more non-crystallized silica. Because obsidian is not a mineral crystal, technically it is not a true "rock." It is really a congealed liquid. This means that it has irregular, random non-crystalline structure.
Obsidian was found by our ancient ancestors and was exquisite for making stone tools. For this reason it was highly sought after and traded. Perhaps early people recognized the molten process in nature and tried to recreate it. Glass droplets were found in Egypt dating back from 3000 BC, but some scientists think that they may have been the accidental byproduct of metalworking or the glazing of pottery. The first intentional man-made glass was found in the Middle East in Nippur near Mesopotamia and dated back to 1,400BC.
All glassmakers, past and present, have to include three components in their formulas:
· Silica (sand) or silicon dioxide. It is made of silicon bonded to oxygen. Silica has a very strong crystalline structure and requires very high temperatures to melt because the strong bonds must be broken.
· Adding a flux can reduce the high melting point. In glass the flux is sodium carbonate.
· Calcium carbonate is added to glass as a stabilizer, which prevents the glass from dissolving in water.
There are five basic types of glass in use today: glass made for bottles and windows, glass made for lab and bake wear, glass with an even higher heat tolerance, high optical and lead glass, and ancient Roman glass.
Adding different elements to the glass will give it different colors, or properties. The type of glass made for windows and bottles (1) has many different components. Lab and baking wear (2) has much more boronic oxide in it to make it heat resistant. Optical and high leaded glass (3). Glass that has an even higher heat threshold (4) is about 96% silica with barely any flux. Ancient Roman Glass (5) has a little bit of everything, but not as much metal oxides as modern glasses.
Different elements added to the glass can cause dazzling colors to arise. For instance, cadmium and selenium make red, copper and chromium make emerald green, cadmium and sulfur make yellow, and gold makes a ruby red. Boron and aluminum make glass heat resistance and lead gives it properties that are ideal for blocking radiation.
Leaded glass has found a role in art as well as science. In the 12th century “art glass” was developed with the addition of lead to make fine crystal. When light particles pass through leaded crystal it is divide into the many colors of the spectrum because of lead’s high refractive index: causing the crystal to sparkle. Refraction should not be confuesed with reflection. Reflection is the phenomenon when ligh hits and and bounces off and oject at the same angle. Refraction is the phenomenon causesd when light passes through a medium and changes the speed and angle it is traveling at. The refration index is a number given to a medium which represnts how much it slows down light particles. Light does not slow down in a vacum so it has a refraction index of 1.000, while light passing through air slowes slightly and has a RI of 1.0029. Essentially, when light waves hit a medium the waves of light slow down and bend. The more it slows or bends, he higher the RI number. The incident angle is the angle that the light waves hit the surface of the medium. (Any angle other than perpendicular.) The refraction angle is the angle (off perpendicular) that the light is bent at, differing from the angle it came in at. The lead added to the glass makes it very dense which causes the light to slow more dramatically and refract at a far more acute angle than unleaded glass.
Because many of the glass products used in the world today take advantage of the way glass treats light energy, I think it is important to elaberate on the properties of light that have relevence in this paper. Light is the most important part of our reality. Everything we persive and almost everything that grows is all thanks to the reaction of light waves. The most improtant aspect of light on earth is the way it bends breaks up, reflects, and is obsorbed by objects around us. I find it interesting that what we see as a color in anything we look at is really the particular wave lenghth that bounces off and reaches our eye. For instance an apple is not really red. It just absorbes all the other wave lenghths of light and the red is reflected and taken in by our eye.
White light contains all the visible wave lengths of light. When we see the white highlighted spot on a shiny apple it is merely the point where all the waves of visible light are bouncing off the apple at an angle to reach our eyes.
The higher frequencies of light (violet to blue) are refracted more than the low frequencies (reds and oranges). One of the strangest things about light is that it behaves as both a wave and a particle. These two behaviors are key to understanding the discussion of refraction index. Most forms of energy have to have a medium in order to work, like sound, (sound is the compression of air paricles) but light needs no medium. In a vacume light is the fastest speed in the universe.
In the early 20th century it was discovered that the dense lead molocule could also be used to shield us from radiation. Leaded glass is a crucial part in the production of television because it allows us to make the tv tube safely. Inside of a TV is a device called a “cathode ray tube”. This is what produces the picture on the screen and along with that process comes harmful x-rays. Inside the Television is a heat source, like the filament of a light bulb that produces electrons, which are aimed in a focused beam towards the screen. This beam of electrons hits the phosphorescent glass of the screen and turns the energy into light and creates the picture. Black and white TVs only have one electron gun, but a color TV has three electron guns, one for each color that the human eye can detect: green, blue, and red. On the outside of the ray tube is a cone of glass with 23% lead content that protects the viewer form the harmful radiation produced in the process.
Unfortunately, with the advent of flat screen TVs we now have millions of older tube-style TV’s ending up in the landfills. However, one cannot just throw out one of these devices because the tube is considered “hazardous waste”. It must be carefully taken apart and the sections disposed of or recycled separately. Fortunately, several new ideas are being developed to recycle the leaded glass. The most promising seems to be its use as a ground up component of concrete, to be used in the building of rooms in hospitals that need radiation-proof walls.
Glass was paramount to other great technological advancements throughout history. Without the infinite potential of glass there would be no Sears Tower, no PBS, humans would not know the secrets of the cosmos, and there would be no way of texting my grandma about how much fun the Diablo Glass School was. It has an amazing role in history art and science. Above all else my hands will never forget the feel of the glass as I twisted and shaped it into the beautiful paperweight that is sitting on my desk right now.