Glass is a material that humans have used since the beginning of their history. First, they used what nature produced spontaneously. Later, they learned how to make it themselves. Glass elements are everywhere – in construction, vehicles, furniture, fashion, electronic devices, in the kitchen, bathroom, and bedroom... It's worth knowing the history of this everyday material and learning how and from what glass is made!
Glass in human history
Scientists confirm that glass has accompanied humans for at least six thousand years. Archaeologists have discovered that civilizations that developed near volcanoes knew and used natural glass. Legends say that human production of glass began with accidentally throwing sand into a fire, but this has never been confirmed.
Interestingly, glass factories existed as early as the 13th century BC! Initially, these were colored, impure vessels or decorative glass pieces. Later, the Romans developed a method for producing clear, colorless glass. The Egyptians applied glass coatings to ceramic vessels and then blew complex forms, such as flasks and goblets. They noticed that if they applied a drop of glass to one end of a thin, long tube and blew from the other side, a bubble would form. Later, they learned how to shape the glass bubble appropriately.
Towards the end of the Middle Ages, the first window panes began to be created. They were called "gomółki" (rounds) and were also made by blowing. The bubble was flattened and attached to an iron rod, which was then rapidly spun. The glass transformed into a circle. This was then cut to the appropriate size. This technique was refined. Dyes were added to the glass to create beautiful stained glass, which can still be admired in European churches today. Furthermore, glass was used to make vessels, ornaments, jewelry, and vases and flasks. Despite inexpensive materials, the production process was time-consuming, and the objects made from it were only available to the wealthiest. It's no coincidence that there's a superstition about seven years of bad luck after breaking a mirror – mirrors, like other glass products, were simply a huge expense for a family.
It wasn't until the turn of the 19th and 20th centuries that a method for cheap industrial glass production was invented. First, in 1913, Émile Fourcault invented a method for producing drawn glass by pulling a thin ribbon of glass using a nozzle from a glass-filled tank, forming it, and then slowly cooling it. Soon, an improved method, called the Pittsburgh process, was developed – in a new, slightly more complex machine, nozzles were no longer needed. Drawn glass is still produced in some places. Although the sheet is very thin, it has defects related to waviness, bulges, and other distortions. This affects the image seen when looking through this type of glass.
Despite its flaws, glass could finally reach the masses, being used on a large scale for the production of windows, ornaments, jewelry, dishes, everyday objects, and in many other industries. Today, the Pittsburgh method is being replaced by the float method ("Pilkington process"), and clear and flat glass is the standard, even with low product prices. How is glass made today?
Glass components
What is glass made of? Its production primarily requires quartz sand and high temperatures. Quartz sand is the most common sedimentary rock on Earth, extracted for industrial production from special deposits. For the production of traditional glass, various additional chemical compounds are also added to ensure its colorlessness or to affect its durability and strength. However, to obtain glass of a specific color, metal oxides must be added, e.g., iron and chromium for green, manganese for violet, or cobalt for blue. This is how both colorful glass vessels, including beautiful decorative vases, and stained glass are created. Glass cullet, or recycled glass, is also used in glassworks.
Types of glass
Glass is divided into several types – some are suitable for windows, others for glasses and goblets, still others for light bulbs, spectacles, or lamps. Window glass is used in construction. It is transparent, unlike colored glass or opaque glass, which is used for things like architectural tiles. Tempered glass is resistant to sudden temperature changes – it is used, for example, for heat-resistant dishes. Laminated glass is used in the production of car windshields. Reflective glass is used on facades. Glass can also be electrically conductive. Ceramic glass is used in electric stoves and fireplaces. Finally, glass is also used to create glass wool or glass fibers – so important in the production of optical fibers.
Production and forming of glass vessels
What is the glass for vessels such as goblets, glasses, decanters, vases, or platters made of? Glass processing begins with preparing the appropriate proportions of ingredients. These are: sand, sodium carbonate, dolomite, aluminum oxide, and clarifying or coloring agents. Glass cullet can also be used.
The mixture is placed in a furnace for 24 hours at a temperature of 1500 degrees Celsius. The liquid leaves the furnace through special pipes and, still hot, in the portion needed to form the vessel, goes to another part of the machine. There, a bubble is mechanically blown. Then it goes into a mold, which gives the vessel its appropriate shape – what a human once painstakingly did with a straw, today is done by machine parks. Molds can have embossments – a logo, company sign, or decorations that appear as raised patterns on the final product. After forming, the glass is heated and then very slowly cooled. In the most modern machine parks, a special camera system performs quality control of the vessels – checking for bubbles and irregularities. The glass production process concludes with one more check, during which faulty products from the series that the machine missed are eliminated by a human.
Handmade glass
There are still factories, such as Krosno Glassworks, that produce hand-formed glass. This allows for the creation of unique products that reflect artistic visions and the individual needs of the end user. This way, one can obtain glasses, goblets, or candle holders with unusual forms that cannot be achieved with automatically formed glass. Similar materials are used for its production, but the process itself is much more time-consuming, and the series of final products are short. Thanks to the "handmade glass" label, users can be sure that they are using original vessels that no one else possesses.
