What is Glass?
1. MOTHER NATURE WAS MAKING GLASS LONG BEFORE HUMANS EXISTED
Lightning strikes on the sand of beaches and deserts is one way we see glass in nature. These glass rods are called fulgurites. Volcanic eruptions also create glass, when lava flows hit sand and rocks, these heat sources turn them into obsidian ( the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded.). Scientists have even found glass of extraterrestrial origin, most likely carried to Earth by meteorites or comets.
2. GLASSMAKING MAY HAVE BEEN DISCOVERED BY ACCIDENT BY ANCIENT PEOPLES
Roman author and natural philosopher Pliny the Elder suggested that ancient traders may have accidentally discovered a rudimentary technique for glass making. In his Historia Naturalis, written around 77 AD, he relates a story of sailors stopping on a beach to prepare a meal, and using lumps of soda to support their cooking cauldrons. When the heated soda mixed with the sand of the beach, according to the story, the first manmade glass was formed. Ancient Egyptians or Mesopotamians may have also discovered how to make glass even earlier, in the process of firing clay to make pottery.
But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or ancient Egypt.[2] Because of Egypt's favorable environment for preservation, the majority of well-studied early glass is found there, although some of this is likely to have been imported. The earliest known glass objects, of the mid-third millennium BCE, were beads, perhaps initially created as accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing
3. GLASSBLOWING IS AN ANCIENT ART
The earliest known evidence of glassblowing was found by archeologist Roman Ghirshman in the Chogha Zanbil ziggurat complex in the Khuzestan province of Iran. During the excavation of the site, which dates back to the 2nd millennium BC – more than 3,000 years ago, numerous glass bottles were found. The technique by which these bottles were made isn’t known, so it’s difficult to say if they were created using techniques we now know as glassblowing.
Encyclopedia Britannica
Glassblowing was invented by Syrian craftsmen in the area of Sidon, Aleppo, Hama, and Palmyra in the 1st century BC, where blown vessels for everyday and luxury use were produced commercially and exported to all parts of the Roman Empire. At first, glass was blown into decorative molds; vessels shaped as shells, clusters of grapes, and human heads were common early Syrian products, but later Syrian gaffers (blowers) executed natural, spherical forms, without the use of molds.
From “working the flame”
After much debate, most historians agree that the true manufacturer of glass and discipline of glassworking likely began in ancient Egypt around 1500 BC and was adopted shortly thereafter by the people of Mesopotamia. The Egyptians made small glass items such as beads, figurines, and tiles. These tiles were considered both decorative and functional and covered the walls and floors of most temples.
Shades of royal blue and turquoise were some of the most popular colors for glass because they resembled the semi-precious stones lapis lazuli and turquoise that held great value in early civilizations. The colors and general appearance of the tiles had aesthetic value but also protected the surfaces of temples from damage.
“Malqata Kateriskos” Vessel, circa 1450 and circa 1350 BC (New Kingdom of Egypt.)
Ancient glassworkers developed and refined their craft over an extended period of time through experimentation with silica sand and quartz pebbles. It is likely that the work of other craftsmen like potters and metalworkers inspired early glass artists to experiment with heated glass.
Glassworking in ancient times did not resemble glassblowing as we know it today. The process began by making hunks of glass that were then shipped to faraway workshops to be crafted into finished products. Once in the workshops, craftsmen used molds, fusing, grinding, and core-forming techniques to form the rough glass pieces into functional and decorative items. Artisans added copper oxide and cobalt oxide to the glass to create the shades of blue that were so popular during this period.
Making glass is described on a clay tablet from the library of King Ashurbanipal (668-627 b.c.). Zunkir / CC BY-SA
What we know of the glassmaking process during the time of the ancient Mesopotamians is found on clay tablets, many of which from the library of King Ashurbanipal (668-627 b.c.), now located in the British Museum. The 3,300 year old instructions for making glass detail the materials needed and the entire glassmaking process. Sand, soda ash, an unknown “white plant,” and a copper compound were listed as necessary ingredients in the ancient glass recipe.
4. THE ROMAN EMPIRE SPREAD GLASSBLOWING THROUGH THE ANCIENT WORLD
Glassblowing as it is known in the modern world was invented during the Roman Empire in the first century BC. The art was developed and spread with the support of the Roman government, with the first large glass workshops established by the Phoenicians on the eastern borders of the empire, in areas which are now Israel and Lebanon. Glass objects became more common during the Empire, as both functional devices and works of art.
Blown glass jug, among the first examples of Ancient Roman colourless glass.
The Romans recognized the profits to be made from glass. Although relatively cheap to make, glass could be traded with gold.
By the 2nd century CE, glass products spread throughout the Middle East as a popular trade item. The Greeks honed the technique of producing glass on a pipe (the glassblowing practice still done today) and glassmaking became a competitive market.
Glassworking Throughout the Middle Ages
An example of blown glass from the island of Murano, Italy. Vassil / CC0
After the fall of the Roman Empire, glassworking continued to gain popularity in medieval Italy. By 1200, Venice dominated the glassmaking industry. The city had access to high-quality sand and abundant forest for raw materials and fuel.
At one point in the height of their success, the Venetians decided to move production to the island of Murano to safeguard their glassmaking secrets. Word made its way around Europe regardless, and by 1400, the French, Germans, and others across the continent were making glass.
In the later middle ages, glassworkers developed several important innovations. Flat glass was invented by creating a glass cylinder, cutting off its ends, and then flattening it to create one continuous sheet of glass. Thus, windows were born!
The process of making crown glass window panes was perfected by French glassmakers in the 1320. böhringer friedrich / CC BY-SA
Cathedral workers in France learned how to produce new colors for their windows, building on previous knowledge about glass additives and colors.
As science and the study of experimental science became mainstream in the 17th century, new uses for glass included the invention of microscope lenses and laboratory glassware.
This forced glassmakers to experiment with new additives to create stronger, heat and chemical resistant glass. In 1676, lead glass was invented. By adding lead to glass, craftsmen produced a glass that proved stronger and shinier than its counterparts. The mixing of glass with other materials became common in the 17th century and would continue to be a popular practice in the glassmaking industry moving forward.
Glassblower with a Hessian crucible in the background, as per historical descriptions of the Jamestown colony.
Glass made its way to the New World in the 1600s on the ships of colonists. Glass production started in America shortly after and the abundance of sand and timber on the continent encouraged glassworkers to make and sell a variety of items.
Studio Glass Movement of the 1960s
Dominick Labino (pictured), and Harvey Littleton, contributed hugely to the studio glass blowing movement.
The attitude toward glass shifted in the 1950s and into the 1960s as craft media gained popularity across America. Old-fashioned and handmade items regained interest after World War II. In 1958, a ceramics professor at the University of Wisconsin-Madison named Harvey Littleton started experimenting with glassblowing on a small scale.
Dominick Labino, an inventor and fellow glass artist, helped Littleton create the first personal glass blowing furnace. It was small enough to sit in independent workshops and studios and heated to the proper temperature for artistic glass blowing projects.
In 1962, with help from Labino and the Toledo Museum of Art, Harvey Littleton hosted the now-famous studio glassblowing workshops that marked the beginning of the studio glass movement.
Harvey Littleton created sculpted glass that defied decades of purely functional glass products. Sailko / CC BY
Littleton started the United States’ first college glass program at the University of Wisconsin-Madison and some of his first students included Dale Chihuly and Marvin Lipofsky. Littleton and his students experimented with glass in ways never seen before.
TYPES OF GLASS FOR GLASS BLOWING
General Glassblowing & Lampworking Glass
Glass without additives is called quartz glass. Petar Milošević/ CC BY-SA
Standard glass is made by melting sand or quartz. Glass without additives is called quartz glass and has a very high melting point, making it expensive and difficult to work with. Additives called fluxes are used to lower the melting point of glass. Common fluxes are soda ash, potash, and lime.
While helpful in creating more workable glass, fluxes can make glass unstable and prone to forming unwanted crystals. Stabilizers like limestone and zinc oxide are added to glass to counteract the negative side effects of fluxes.
The two most common types of glass used in glassworking today are borosilicate, or “hard” glass and soda-lime or “soft” glass. Each are readily available and have their own pros and cons when used for glassblowing, lampworking and other glass art techniques.
1) Borosilicate Glass (“Hard” Glass) Expensive but Durable
Hedgehog from borosilicate glass. Photo by Amanda WalkerCC BY-SA
Borosilicate glass is made of silica with at least 5% boric acid in its overall composition. It has a high melting point and is very resistant to temperature changes and chemical corrosion. Borosilicate glass melts at around 820 degrees Celsius and is easily worked at 1,200 degrees Celsius.
Borosilicate glass is a moderately priced glass due to its method of production and its durability. It is commonly used to make laboratory ware, bakeware, microscopes, and telescopes when used commercially. Lampworking artists use borosilicate glass for a variety of projects such as jewelry, marbles, sculptures, and decorative lighting.
2) Soda-lime Glass (“Soft” Glass) 90% of Glass Production
The most common and inexpensive glass used in glass art is soda-lime glass, or soft glass. Made from 60%-75% silica, 12%-18% soda, and 5%-12% lime, this glass is chemically stable, hard, and workable. It also has the ability to be re-melted, making it very versatile in the studio.
The softening range for soda-lime glass is 696 degrees Celsius and the working range for this type of glass is 1,000 degrees Celsius. These relatively low temperatures make soda-lime glass a great option for lampworkers using torches. Soda-lime glass can be used for almost any project, and can be found at glass retailers for affordable prices.
Glass Colorings
By Anne Marie Helmenstine, Ph.D. Updated on July 27, 2018
Early glass derived its color from impurities that were present when the glass was formed. For example, 'black bottle glass' was a dark brown or green glass, first produced in 17th Century England. This glass was dark due to the effects of the iron impurities in the sand used to make the glass and the sulfur from the smoke of the burning coal used to melt the glass.
Man-made Glass Coloration
In addition to natural impurities, glass is colored by purposely introducing minerals or purified metal salts (pigments). Examples of popular colored glasses include ruby glass (invented in 1679, using gold chloride) and uranium glass (invented in the 1830s, glass that glows in the dark, made using uranium oxide).
Sometimes it is necessary to remove unwanted color caused by impurities to make clear glass or to prepare it for coloring. Decolorizers are used to precipitate out iron and sulfur compounds. Manganese dioxide and cerium oxide are common decolorizers.
Special Effects
Many special effects can be applied to glass to affect its color and overall appearance. Iridescent glass, sometimes called iris glass, is made by adding metallic compounds to the glass or by spraying the surface with stannous chloride or lead chloride and reheating it in a reducing atmosphere. Ancient glasses appear iridescent from the reflection of light off of many layers of weathering.
Dichroic glass is an iridescent effect in which the glass appears to be different colors, depending on the angle from which it is viewed. This effect is caused by applying very thin layers of colloidal metals (e.g., gold or silver) to the glass. The thin layers are usually coated with clear glass to protect them from wear or oxidation.
Strange behaviors in Glass led to Photography…specifically
Silver compounds such as silver nitrate and silver halides can produce a range of colors from orange-red to yellow. The way the glass is heated and cooled can significantly affect the colors produced by these compounds. Also photochromic lenses and photosensitive glass are based on silver. Glass using silver halide and silver nitride will reveal the shadow of what was inside if it is heated to 500F (250C) after exposure to UV light.
Glass Pigments
Compounds | Colors |
iron oxides | greens, browns |
manganese oxides | deep amber, amethyst, decolorizer |
cobalt oxide | deep blue |
gold chloride | ruby red |
selenium compounds | reds |
carbon oxides | amber/brown |
a mix of manganese, cobalt, iron | black |
antimony oxides | white |
uranium oxides | yellow-green (glows!) |
sulfur compounds | amber/brown |
copper compounds | light blue, red |
tin compounds | white |
lead with antimony | yellow |
Frit
Frit is a common material used in lampworking. Frit is created through physical alterations instead of the addition of certain chemicals. It is essentially just colorful, ground up glass.
Despite its simplicity, frit has important uses in creating decorative, multidimensional beads and jewelry elements. Frit comes in a variety of colors and is added to hot glass to make bright, unique swirls and spotted designs.
Dichroic Glass
Photo by Julie Redmond CC BY-SA
Another variation of borosilicate and soda-lime glass is dichroic glass, which is commonly used for beads, jewelry-making, and vessels. This glass shows up as two different colors depending on the lighting. Color changing glass has been around since the 4th century.
Today, dichroic glass is made by layering metals such as titanium, aluminum, and magnesium and vaporizing them in an electron beam in a vacuum chamber. Finished dichroic glass can be made of 30 to 50 layers of metals.
TOOLS of the Trade
1) Furnace/Glory Hole
Most glassblowers rely on furnaces as their sources of heat. Furnaces used today are typically gas-powered and reach temperatures of 2,000 degrees to 2150 Fahrenheit (1180C). Each furnace has a glory hole and an opening in the furnace where glass is gathered and reheated.
2) Benches
Photo by amanderson2 CC BY-SA
The bench is the place where a glassblower performs much of his or her work. Benches are usually made of a mix of wood and metal. Benches have arms to support the blowpipe and glass project and hold the other small tools glassblowers use through the glass making process.
3) Yokes
Photo by Bruce Tuten CC BY-SA
A yoke is a stand that is placed in front of a glassblower’s furnace to support pipes as they enter the glory hole. The pipe is set on the yoke to keep it steady and guide it into the furnace to gather glass.
4) Annealer
An annealer slowly cools a finished glass product so it does not shatter. The annealer creates a controlled environment in which the glass can very slowly cool and harden to room temperature generally around 900F or 480C. Without the annealer, glass would cool too quickly and break. Annealers can be compared to kilns used by pottery artists.
Small Equipment Used in Glassblowing
The precise nature of glassblowing requires many small tools with unique functions. Depending on the type of item being created, only a few of these tools will be used at any given time. For more detailed glass blown products, artisans may rely on many of the following to achieve the desired outcome.
Most glassblowers are familiar with a wide range of tools and how to use them. The more experienced a glassblower is with different tools, the more items he or she can create and the more valuable he or she is within a studio or workshop. The following is a comprehensive list of the most popular small tools used by glassblowers and lampworkers.
5) Blocks
A block is a wooden tool used for shaping gathers of glass. After a glassblower gathers hot glass from the glory hole, he or she takes the glass over to a bench to begin working it. Blocks are soaked in water to create a layer of steam when in contact with hot glass. They help form glass into a rounded, even shape to prepare it for inflating and further shaping.
6) Blowpipe
Photo by Craig Hatfield CC BY-SA
Blowpipes are used to blow air into glass and inflate it. Used during the beginning and middle stages of the glassblowing process, blowpipes are hollow and metal with a mouthpiece on one end and a place for hot glass to gather at the other.
7) Torches
Photo by endlesspics CC BY-SA
Torches are the equivalent of furnaces for lampworkers, but can also be used in glassblowing while moulding the workpiece.
In terms of lampworking, because they work on a much smaller scale, lampworkers rely on the heat of torches to soften and shape glass. While any torch technically works for lampworking projects, serious artisans use torches specifically made for glassworking. These torches have more precise flames and heat to the appropriate temperatures.
8) Jacks
Photo by Craig Hatfield CC BY-SA
Jacks are a pair of metal blades held together at the end with a curved handle. They look like large tweezers and are used to shape glass as it is rotated at the workbench. Jacks can be used to shape glass as it is being inflated, separate glass from the blowpipe towards the end of the work process, and widen the opening of glass vessels.
9) Shears
Shears are used to cut or constrict hot glass. They come in two types: straight and diamond. Depending on the type of project being completed, glassblowers will favor one over the other.
10) Paddles
Photo by Anne Jacko CC BY-SA
Made from wood with a handle at the end, paddles are used to form the bottom or other flat edges of glass pieces. The glass is carefully pressed onto the paddle to create a flat surface.
11) Molds
Photo by Dennis Jarvis CC BY-SA
Molds are used to shape glass into preset shapes and items. Molds are generally made from brass or wood and can be custom made to suit the needs of individual glass blowing projects.
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INTERESTING COCKTAIL FACTS
5x Stronger Than Steel
A flawless fiber of glass pulled lengthwise is five times stronger than steel! Although glass is quite strong, it's also very brittle and the brittleness explains why glass breaks so easily.
But windshields in cars and airplanes are much more resistant to breaking than regular glass.
What Makes Windshield Glass So Tough?
Glass is commonly made more resistant to breaking in one of two ways: by tempering or by laminating it. Tempered glass is first heated just below melting, then exposed to bursts of cold air. The cold cools and shrinks the surface of the glass faster than the inside, compressing the surface inward.
This more dense, inwardly compressed surface makes the glass stronger, so it takes a lot more force to break it. Tempered glass shatters into tiny bits, rather than large, jagged shards like regular glass. If you've seen little squares of a car windshield scattered on the street, you've seen how tempered glass shatters.
Laminated Glass
Car windshields are also commonly made from laminated glass, which has a tough, thin layer of plastic sandwiched between two layers of glass. If laminated glass shatters, it remains sticking to the plastic rather than scattering in splinters or shards.
Airplane windshields and bullet-resistant glass take this concept to a whole new level, with several layers of plastic layered with, and bonded to, layers of glass. That makes a composite material strong enough to withstand high pressures, varying temperatures, and even the impact of a bullet or an unlucky bird.
Glossary:
Fulgurites: glass made by lightning
Glory Hole: glass reheating and collecting furnace for glass
Soda glass: a common form of soft glass which is relatively easy to melt and easy to form. 90% of which is used in everyday household items.
Blowpipe: a stainless steel pipe for collecting and forming glass.
Murano: the island near venice where glass blowers were kept hidden from the world to practice the craft of glass-blowing
Lampworking: the creation of glass art using an oil-lamp though torches are used today, may be traced to 5th century BC as well as during the times of the Murano glass factory
Tempered glass: heat treated glass that takes advantage of the amazing tensile strength of glass to form safety critical items like glass windshields.
NOT Glassblowing but interesting…
19th Century Glassworking & Glass at the Turn of the Century
Crockery and glass journal (1875).
The industrial revolution in Europe and America altered and automated glass production. In 1820, the mechanical press was invented, making it easier and cheaper to make glass products than ever before. As soon as two decades later, glass became a common household item among people of all social classes.
In the 1880s, the Germans invented borosilicate glass, or Jena glass that could withstand high temperatures and a range of harsh chemicals. Beakers, bottles, and other laboratory glassware was blown thin to prevent thermal shock when used in lab settings.
The invention of Pyrex popularized bake-ware and baking Image from American cookery (1915)
Outside of the scientific community, glass innovations made strides in resolving economic demands and social issues. 1903 saw the invention of the automatic bottle blowing machine, which cut production costs by 80% and helped end child labor in the glass industry.
The development of heat-resistant Pyrex in the 1920s popularized glass bakeware and other cookware. Now, every home uses glass items for cooking and dining. While glass art existed during the early 20th century, most people viewed glass items as necessities to be used daily for practical things.
References:
Historical
Most of the material in this piece is from this site:
Cocktail facts
Color science
Helmenstine, Anne Marie, Ph.D. "Colored Glass Chemistry: How Does It Work?" ThoughtCo, Aug. 25, 2020, thoughtco.com/the-chemistry-of-colored-glass-602252.
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