Glass is a beautiful and useful substance. It occurs naturally in the form of obsidian, tektites and other forms. It has been used by humans for thousands of years as tools and ornaments. It was well known in the ancient world and was highly prized because of its beauty and rarity. The Bible contains several references to glass such as, “Gold and glass cannot equal wisdom,” Job 28:17. While it has been known and used for millennia, prior to the common era it was generally only the wealthy that could afford it. Its usefulness was mostly aesthetic. During the Stone, Bronze, and Iron ages glass was a novelty.
So many new forms of technology have been developed in the last century alone we have multiple “age” names to describe it including atomic age, space age, computer age, information age, etc. While these names are descriptive of very important technologies and advancements, one substance has arguably made them all possible. Its use covers a much larger span of recent history and almost single-handedly made the scientific revolution possible over the past 500 years. What is this magical substance? Glass of course.
Many people are familiar with the beautiful intricacy of artisanal Roman glassware. Man-made glass stretches back long before the time of the Caesars and even before Alexander the Great. Glass beads were being made possibly as far back as 3000 BCE. Primitive glass making arose in India by about 1750 BCE and the first glass vessels were made around the 15th century BCE. Also by the 15th century, extensive glass production was occurring in Western Asia, Crete, and Egypt. Glass was primarily made by either pouring it into a mould or core-forming. Core-formed means the glass was heated and formed around a central core that provided the shape. These processes required great time and skill and so glass was so expensive it was accessible only to the upper classes. It would have been a fairly rare substance compared to other material such as stone, pottery or metal.
The Stone Age is often said to end around 550 BCE. The end date is not exact and varies widely by region. For example, Western and Central Europe are thought to remain in the Stone Age until about 50 BCE. This timespan aligns nicely with the transition to the glass age. While the main glass age would not begin until around the 13th century, we see several technological advances in glass making in the 1600 years prior to that. So I have termed this period the early glass age.
We can date the start of the early glass age to the rise of glass making in the Hellenistic period and the life of Alexander the Great (356-323 BCE). This era marks a major shift in the role of glassware, at least in the region around the Mediterranean. Wikipedia notes, “Glassmaking at this time was based on the technological traditions of the Classical antiquity and the Late Bronze Age, but was marked by transition from limited production of luxury objects made for the social elite to mass production of affordable glass vessels used by the broader public to satisfy everyday needs.”https://en.wikipedia.org/wiki/Hellenistic_glass?wprov=sfti1
So a major hallmark of the early glass age is the transition of glassware into common usage by the lower classes for everyday needs. This is thanks to improved production methods.
During the Hellenistic period many incremental techniques of glass production were introduced. Larger glass pieces, notably table wares, became possible thanks to some of these innovations. Wikipedia mentions some of the techniques developed during this period. They include, “'slumping' viscous (but not fully molten) glass over a mould in order to form a dish and 'millefiori' (meaning 'thousand flowers') technique, where canes of multicolored glass were sliced and the slices arranged together and fused in a mould to create a mosaic-like effect.” https://en.wikipedia.org/wiki/History_of_glass?wprov=sfti1
During the 1st century BC, glass blowing was discovered on the Syro-Judean coast, revolutionizing the industry. This technique helped bring the cost of glassware down. Glassware became cheap and expendable, a kind of Roman plastic. “the discovery of colorless glass (through the introduction of manganese dioxide), by glass blowers in Alexandria circa 100 CE, the Romans began to use glass for architectural purposes. Cast glass windows, albeit with poor optical qualities, began to appear in the most important buildings in Rome.”
Although they achieved relatively clear, de-colored glass, it was not perfect. It had a lot of inconsistencies resulting in low clarity. It looked more like quartz crystal than glass as we know it today. Some areas of a vessel may be cloudy whitish. There may be bubbles or lines that diffract light and obstruct the view. When used as a window it was ideal for letting light through but not for looking out of. https://www.nytimes.com/2020/07/31/science/alexandrian-glass-rome.html
Another innovation that came during the Roman era was the stained glass window. In the second or third century CE Christian churches began using colored glass to make artistic window pictures. These were likely modeled after the mosaics common in Roman villas that adorned walls and floors. https://www.thoughtco.com/stained-glass-4692208 Although not a major technological leap, it had important cultural significance. It helped unify Christian teachings and spread the stories of the Bible to an illiterate populace. It highly influenced architecture and art as well.
Around 1000 CE, potash-lime glass (sometimes called forest glass) was discovered in northwestern Europe. It was made by using potash from wood rather than soda and ever so slowly began to replace soda-lime glass. It has a higher melting point and is significantly stronger than soda-lime glass. Thus it was more desirable. One of its first major uses was in stained glass windows. Because of its improved durability, stained glass windows could be made wider and with larger pieces. This contributed to the rise of Gothic style stained glass art. https://en.wikipedia.org/wiki/Forest_glass?wprov=sfti1
Thus we see many important breakthroughs were made in the early glass age that were key to perfecting glass materials and science. In the next section we will look at the main glass age and see how glass technology revolutionized not only glassware, but also humanity’s fundamental ideas about the world.
Glass held an important place in Medieval Europe. Stained glass was central to European Catholic life from the 13-16 century as a key part of the cathedral, the center of society. It was a means of educating the illiterate masses through narrative mosaics. Mirrors also played a key role in European aristocratic life enabling people, especially women, to spend hours a day perfecting their appearance. Mirrors also seem to have played a significant role in spiritual matters.1 In fact, after Johannes Gutenberg lost his revolutionary printing press to debt collectors, he turned to making mirrors sold to pilgrims for use in spiritual rituals.
The main Glass Age could be considered to start with the invention of turely colorless, transparent glass around 1430.2 Although glassmaking had been around for millennia, the ability to reliably make colorless glass that's highly transparent is what has led to so many technical and scientific breakthroughs. Thus we need a distinction between the early and main glass ages. Around the same time as the perfection of colorless glass, the art of blown glass grew in earnest in Venice, Italy. Blown glass had been around since about 1 CE, but in Venice, several significant breakthroughs took place in a short time.
In 1271 the glassmaker’s guild was formed. In 1291, officials passed a law that required all glassmakers and glass artisans to move to the island of Murano. It also forbade them to leave or any foreign glassmakers to make or sell glass in Venice. This concentration of highly skilled craftsman led to Murano becoming the world leader in glass making and likely contributed to the major advancements in glass technology. Around 1430 a skilled glassmaker named Angelo Barovier invented a process for making extremely transparent glass.3 It was known as cristillo, and this unclouded see-through glass led to the development of many technologies.4
The most important glass tool resulting from the main Glass Age is the lens. The invention of transparent glass enabled better lenses to be manufactured for many applications. Eyeglasses were invented and became common in the 13-14th centuries, but these mostly used lenses made of quartz. Glass proved to be a superior material for making precise eyeglasses that suited the wearers needs.5 Alongside the invention of the printing press, spectacles were helpful in the spread of ideas through reading because about 75% of adults requires vision correction. Reading was a major cornerstone of the renaissance and the scientific revolution. Reading became so popular after the Gutenberg printing press the first spectacle specialty shop was able to open in Strausberg in 1466. 5a
In 1632 Galileo published his finding confirming the sun was the center of the solar system thanks to the telescope he perfected. In 1665 Robert Hooke first described and named the cell of living organisms after many years of observations with a microscope. The lens eventually led to the invention of the camera which enabled improved documentation. It led to revolutions in science, art, entertainment, education, history, and communication and is a central technology of the Information Age (20th - 21st century).
In 1514 Johannes Werner suggested the cross-staff, an instrument for measuring the position of celestial bodies, be used for sea navigation. It was widely adopted shortly after and played a key role in the Age of Discovery (15th – 17th century). The user was required to look directly at the sun in order to calculate its angle to help determine the ships position. Repeatedly looking directly at the sun was painful and so navigators began fixing smoked glass lenses on their cross-staff to reduce the brightness of the sun.6
Transparent glass improved navigation in other ways. The basic navigation compass had been used in primitive forms for millennia. Transparent glass enabled more sensitive and accurate forms to be protected inside wood boxes and brass bezels. One example is the dry compass which could be used accurately in swaying, rocking ships. The compass was also adapted for surveying and cartography. The compass was a key part of the theodolite invented in 1571 by Joshua Habermel, an instrument that is still a part of land surveying today.7 After Habermel’s death an optical scope was added to improve visual range and accuracy.
The surveyor’s compass, also known as the circumferentor, was another adaptation of the basic navigation compass that was central to surveying and cartography for centuries. It was eventually replaced by the more portable prismatic compass in the 19th century. The accuracy of the navigation compass was greatly improved with the invention of the liquid compass in 1690 which is nearly universal today.8
Glass prisms and lenses were incorporated into other navigation tools increasing their accuracy and ease of use. The sextant was invited in 1731 replacing the marine astrolabe and cross-staff. This major innovation allowed navigators to sight the nighttime celestial bodies and acquire their location even when the sun was not shining—a major advantage. These advancements, in turn, improved navigation accuracy reducing travel time thereby increasing trade and the spread of ideas.9
Another key area glass changed was timekeeping. The hourglass made timekeeping easier and more precise. The exact origins of the hourglass aren't clear, but it's generally accepted that it was widely adopted in Europe by the end of the High Middle Ages (around 1500 CE). The hourglass was a popular choice for sailors who used it to mark the passage of time, which allowed them to determine their longitude. The hourglass was preferred over earlier water clocks because their sand was unaffected by the rocking motion of a ship. They were used onshore to measure time for church services, cooking and work tasks. Eventually, mechanical clocks supplanted the hourglass, though it wasn't until the 18th century that a suitable marine replacement was found. Clocks became small enough to fit in pockets around the 16th century. These early pocket watches were prone to exposure to rain. The first pocket watch to be protected by glass was in 1611. Watch makers quickly caught on the the benefits of glass for making their products more durable. Watches have been covered with a clear lens ever since to protect their delicate insides. https://en.wikipedia.org/wiki/History_of_watches?wprov=sfti1
The window is another great example of how transparent glass improved the modern age. Of course, glass windows have been around since the time of the Romans. The true importance of see-through glass windows was not realized until the transportation revolution in the mid-19th and early-20th century. The see-through window enabled high-speed mechanized transportation in boats, trains, cars, and planes in the modern era. Glass windows have developed alongside the transport vehicles they enable. At first glass windows were small, flat, and prone to shatter. Many advancements by numerous individuals have led to modern glass windows that are large, able to be molded into curved shapes, while being shatter-resistant and even bulletproof.
Perhaps the most influential role of glass in the past 500 years is in the area of chemistry. Chemistry’s impact in all areas of life hardly needs mention. Most all the advancements of chemistry would likely have been impossible without glass in the lab. It is not just the transparency of glass that was important to chemistry. More critical is the inert property of glass which enables it to be in contact with nearly any chemical and not react. This allowed chemicals to be isolated and studied. Robert Boyle (1627-91) is known widely as the father of chemistry. Boyle used a large glass sphere to create a vacuum chamber. He observed that when he placed a burning candle inside and removed the air, the candle went out. This undermined the ancient idea that the four elements, air, water, fire, and earth combined in various ways to make up every substance. Boyle proposed a different definition for an element which we still use today and thus invented modern chemistry—all thanks to that glass vacuum chamber.10, 11
The thermometer was invented by Robert Fludd in 1638. It consisted of a long glass tube with a bulb at one end filled with a liquid such as water, alcohol or mercury. This instrument was important to discoveries in the fields of chemistry, medicine, meteorology, and many other disciplines. Although most modern thermometers no longer use glass, their glass ancestors contributed much to our understanding of the natural world.
Better light sources improved night-time activities and extended the usable hours in a day. Metal and glass lanterns became common in the 18th century.12 Advances in fuel types helped improve their brightness and reliability in the 19th century. Coal gas lanterns helped to make cities night-time friendly. Glass panes protected the flame from wind. The Fresnel lens was patented in 1822 and made lighthouses much brighter which meant ships could navigate coastal waters more safely.13 The handheld lantern with its glass globe or lenses was critical to the railroad which began running at night in 1848. Fresnel lenses were common in railroad signal lanterns. The handheld lantern also lit many homes until the electric light fully replaced it in the mid-20th century. Handheld lanterns are still an important tool for recreational camping today. The electric light bulb was invented by Thomas Edison in 1879. In fact, Edison blew his own glass bulbs for his experimentation.
Glass bottles and jars revolutionized food, beverage, and medicine storage and transportation in the 19th century. Canning was invented by a French chef in 1806. However, their seals frequently failed. The canning jar was perfected by John Landis Mason in 1858. Several companies were producing canning jars by the late 1800's which significantly improved food storage commercially and at home. Bottle making technology experienced many improvements also. Glass bottles were in such high demand by the end of the century that the first fully automatic glass forming machine was invented to make bottles. Work began on this revolutionary machine in 1898 by Michael Owens. It was completed in 1903 and could make more bottles in one hour than an expert glassworker could make in a day. Before long many types of glass products were made by machine instead of people.14
Glass also revolutionized mass communication. In the early 1800's the telegraph drastically sped up communication time. But it required a professional operator and allowed only two people to talk at a time. Telephone, radio, and recorded sound technology became available towards the end of the 1800's. But these all suffered from a major problem, their signal strength was faint and decreased with distance. Telephone and radio signals were only able to transmit a short distance. That all changed in 1907 when Lee De Forest invented the audion, more correctly called a triode. This device contained sensitive electrical components that could only operate safely inside a vacuum sealed tube made of glass. The triode allowed an electrical signal to be amplified or relayed to great distances. Amplification meant a radio could be played over a loud speaker rather than just headphones. Telephone signals could be carried across the country. Thus mass communication was born. By the 1920's people no longer had to depend on professional telegraph operators, they could receive news directly in their own home on the radio.14a They could call their friends or families directly and hear their voices. They could play recordings over a loud speaker as well. It was no longer necessary to wait for a famous musician to come to town or even for the songs to come over the radio.
These vacuum tubes made numerous electronics possible from long distance telephone and radio, to sound recordings, radar, television, and eventually, digital computers. The television is perhaps the most important means of mass communication invented. Television was made possible by two glass vacuum tubes. One, the Braun tube later known as the cathode ray tube or CRT which allowed electrical signals to project an image on a screen. Two, the triode mentioned earlier made it possible to amplify a visual signal so it could be projected. The Braun tube (CRT) was invented in 1897 by Karl Ferdinand Braun.14e The first electronic television was demonstrated by Philo Taylor Farnsworth in 1927.14f This technology became ubiquitous as TV's found their way into every home.
The first vacuum tube computer was produced in 1939 by John Vincent Atanasoff and Clifford Berry. These large digital computers made rapid calculations possible and were central to the war effort during WWII.14b Glass vacuum tubes were replaced only 20 years later by smaller solid state transistors that required no fragile glass. In 1959 IBM began to mass produce the first commercially successful fully-transistorized computer, the IBM 1401. These small machines helped bring the computer to the masses. No longer were they room-sized devices that only militaries or universities could afford. While glass was phased out of one part of the computer, it was not fully eliminated. It simply transitioned into the monitor.
The 1401 and other computers of the era were controlled through punch-card systems. Paper cards with specially placed holes were fed into the computer to input data, the computer then ran it's functions and output data on other punch-cards. That began to change in the 1950's when the U.S. military contracted with Michigan Institute of Technology and others to install the SAGE computer system. This is considered the first computer to use glass cathode ray tube monitors to display and input data. It was the brainchild of professor Jay Forrester.14c The cathode ray tube or CRT became the staple of visual display screens in both computers and televisions until the early 21st century.14d Although the CRT is gone for good, monitors and screens still contain glass today. Most flat screens in computers, TV's, and mobile computer devices use either LCD (liquid crystal display) or OLED (organic light emitting diode) technology. Glass is central to the operation of both.
Many of the important developments in glass technology in the past 170 years have been made by the Corning Glassware company. One of their important developments was borosilicate glass which was patented as Nonex. It was one of the first heat-resistant glasses available and was adopted nationally for railroad signal lights in 1908 improving railroad safety. Further research of heat-resistant glass by Corning led to the development of Pyrex in 1915 which is still widely used in cookware and many other applications. In the early 1930’s Pyrex was used to make some of the first glass globes on Coleman lanterns. This strengthened their popularity as a reliable and sturdy light source for rural unelecteified homes and later for the campsites of generations of campers.14e Corning is responsible for inventing many modern glass technologies which are central to the Information Age including fiber optic cables which transmit computer signals at the speed of light, and Gorilla glass which is on the surface of most smartphones, tablets, handheld GPS devices, and other electronic gadgets.15 They are also pushing the development of LCD and OLED screen technology.16.
It could be argued that other substances and technologies are important to our modern age. It is hard to pin one as more important than the others because many modern technologies would not be possible without the wide array of materials we have. So one could argue that the glass age ended and the modern era (1800-present) be termed the Composite Age.