I Can’t Sleep - Glass History for Peaceful Sleep Learning

Episode Date: June 2, 2025

Tonight, we quietly explore the mesmerizing world of glass—from ancient volcanic obsidian to the delicate artistry of modern glassblowing. We'll drift through thousands of years of human ingenuity, discovering how sand transforms into windows, vessels, and works of art that have shaped civilizations. Benjamin Boster gently guides us through the peaceful science of melting, cooling, and crafting this remarkable material that surrounds us in our daily lives. Happy sleeping! Want More? Request a topic: https://www.icantsleeppodcast.com/request-a-topic Listen ad-free & support the show: https://icantsleep.supportingcast.fm/ Shop sleep-friendly products: https://www.icantsleeppodcast.com/sponsors Join the discussion on Discord: https://discord.gg/myhGhVUhn7 This content is derived from the Wikipedia article on Glass, available under the Creative Commons Attribution-ShareAlike (CC BY-SA) license. Read the full article: Wikipedia - Glass. Learn more about your ad choices. Visit megaphone.fm/adchoices

You're listening to a Glassbox media podcast. What if I told you that most of the modern day self-help advice you've been hearing could actually make you worse? The key to a better life isn't about feel-good gimmicks that sound catchy. The Mentally Stronger Podcast gives you access to a licensed therapist who shares science-backed tools that will actually change your life. Hi, I'm Amy Morin, psychotherapist, mental strength trainer, and international best-selling author. In each episode, we cover research-back strategies, like how to stop relying on willpower and start creating habits for lasting change. And the five mental strength-building exercises you can do from your couch.

I also speak to world-class experts like Dr. Nicole Kane, who shares how to permanently heal anxiety by addressing the root cause. With over 200 episodes in our catalog, this podcast is for you if you're ready to crush self-doubt, conquer challenges, and become stronger than ever with therapist-approved strategies that can change your life. Listen to Mentally Stronger with Therapist Amy Morin, wherever you get your podcasts. Welcome to the I Can't Sleep Podcast, where I help you learn a little and sleep a lot. I'm your host, Benjamin Boster, and tonight let's fall asleep learning about glass. Glass is an amorphous, non-crystalling solid, because it is often transparent and

chemically inert. Glass has found widespread, practical, technological, and decorative use in window panes, tableware, and optics. Some common objects made of glass are named after the material, e.g. a glass for drinking, glasses for vision correction, and a magnifying glass. Glass is most often formed by a rapid cooling, called quenching, of the molten form. Some glass, such as volcanic glass, are naturally occurring, and obsidian has been used to make arrowheads and knives since the Stone Age. Archaeological evidence suggests glass making dates back to at least 6,600 BC in Mesopotamia, Egypt, or Syria. The earliest known glass objects were beads, perhaps created accidentally during metalworking. Or the production of faeance, which is a form of pottery,

using lead glazes. Due to its ease of formability into any shape, glass has been traditionally used for vessels, such as bowls, vases, bottles, jars, and drinking glasses. Soda lime glass containing around 70% silica accounts for around 90% of modern manufacture glass. Glass can be colored by adding metal salts or painted and printed with vitreous enamels, leading to its use in stained glass windows and other glass art objects.

The refractive, reflective, and transmission properties of glass make glass suitable for manufacturing optical lenses, prisms, and optoelectronics materials. Extruted glass fibers have applications as optical fibers in communication networks, thermal insulating material when matted as glass wool to trap air, or in glass fiber-reinforced plastic or fiberglass. The standard definition of a glass or vitreous solid is a non-crystalling solid formed by rapid melt quenching. However, the term glass is often defined in a broader sense to describe any non-crystalline

amorphous solid that exhibits a glass transition when heated towards the liquid state. Glass is an amorphous solid, although the atomic scale structure of glass shares characteristic characteristics of the structure of a supercooled liquid. Glass exhibits all the mechanical properties of a solid. As in other amorphous solids, the atomic structure of a glass lacks the long-range periodicity observed in crystalline solids. Due to chemical bonding constraints,

glasses do possess a high degree of short-range order, with respect to local atomic polyhedra. The notion that glass flows to an appreciable extent over extended periods well below the glass transition temperature is not supported by empirical research or theoretical analysis. Though atomic motion at glass surfaces can be observed and viscosity on the order of 10 to the 17, to 10 to the 18th pascales can be measured in glass.

Such a high value reinforces the fact that glass would not change shape appreciably over even large periods of time. For melt-quenching, if the cooling is sufficiently rapid relative to the characteristic crystallization time, then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at t sub g

the tendency for a material to form a glass while quenched is called glass forming ability this ability can be predicted by the rigidity theory Generally, a glass exists in a structurally metastable state with respect to its crystalline form. Although in certain circumstances, for example in adatic polymers, there is no crystalline analog of the amorphous phase. Glass is sometimes considered to be a liquid due to its lack of a first-order phase.

phase transition, where certain thermodynamic variables, such as volume, entropy, and enthalpy, are discontinuous through the glass transition range. The glass transition may be described as analogous to a second-order phase transition, the intensive thermodynamic variables, such as the thermal expansivity and heat capacity, are discontinuous. However, the equilibrium theory of phase transformations does not hold for glass, and hence, the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.

Glass can form naturally from volcanic magma. Obsidian is a common volcanic glass with high silica content formed when felsic lava extruded from a volcano cools rapidly. Impactite is a form of glass formed by the impact of a meteorite, where Moldavide found in central and eastern Europe and Libyan desert glass found in areas in the eastern Sahara. The deserts of eastern Libya and western Egypt

are notable examples. Vitrification of quartz can also occur when lightning strikes sand, forming hollow branching root-like structures called Fulgarites. Trinotide is a glassy residue form from the desert floor sand at the Trinity nuclear bomb test site. Etiope glass found in South Australia is proposed to originate from Pleistocene grassland fires, lightning strikes, or hypervelocity impact by one or several asteroids or commons.

Naturally occurring obsidian glass was used by stone age societies as it fractures along very sharp edges, making it ideal for cutting tools and weapons. Glassmaking dates back at least 6,000 years, long before humans had discovered how to smelt iron. Archaeological evidence suggests that the first true synthetic, glass was made in Lebanon and the coastal North Syria, Mesopotamia, or ancient Egypt. The earliest known glass objects of the mid-third millennium BC were beads, perhaps initially created as accidental byproducts of metal-working slags, or during the production of faeons, a pre-glass vitreous material, made by a process similar to glazing.

Early glass was rarely transparent and often contained impurities and imperfections, and is technically phaence rather than true glass, which did not appear into the 15th century BC. However, red-orange glass beads excavated from the Indus Valley civilization, dated before 1700 BC, possibly as early as 1900 BC, predate sustained glass production, which appeared around 1600 BC in Mesopotamia and 1500 BC in Egypt. During the late Bronze Age, there was a rapid growth in glass-making technology in Egypt and Western Asia. Archaeological finds from this period include colored glass ingots, vessels, and beads. Much early glass production relied on grinding techniques borrowed from stoneworking,

such as grinding and carving glass in a cold state. The term glass has its origins in the late Roman Empire, in the Roman glass-making center of deer, located in current-day Germany, where the late Latin term glausum originated, likely from a Germanic word for a transparent, lustrous substance. Glass objects have been recovered across the Roman Empire in domestic, funerary, and industrial contexts, as well as trade items in marketplaces and distant provinces.

Examples of Roman glass have been found outside the former Roman Empire in China, the Baltics, the Middle East, and India. The Romans perfected cameo glass, produced by etching and carving through fused layers of different colors, to produce a design and relief on the glass object. In post-classical West Africa, Benin was a manufacturer of glass and glass beads. Glass was used extensively in Europe during the Middle Ages. Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. From the 10th century onwards, glass was employed in stained-glassed windows of churches and cathedrals, with famous examples at Chartres Cathedral and the Basilica of St. Dennis. By the 14th century, architects were designing buildings with walls of stained glass,

such as Saint-Chapelle, Paris, 1203 to 1248, and the east end of Gloucester Cathedral. With the change in architectural style during the Renaissance period in Europe, the use of large stained glass windows became much less prevalent. Although stained glass had a major revival with Gothic revival architecture in the 19th century. During the 13th century, the island of Murano Venice became a center for glass making, building on medieval techniques to produce colorful ornamental pieces and large quantities. Murano glassmakers developed the exceptionally clear colorless glass Cristallo, so-called for its resemblance of natural crystal,

which was extensively used for windows, mirrors, ships lanterns, and lenses. In the 13th, 14th, and 15th centuries, enameling and gilding on glass vessels were perfected in Egypt, and Syria. Towards the end of the 17th century, Bohemia became an important region for glass production, remaining so until the start of the 20th century. By the 17th century, glass in the Venetian tradition was also being produced in England. In about 1675, George Ravenscroft invented lead crystal glass. with cut glass becoming fashionable in the 18th century. Ornamental glass objects became an important art medium during the Art Nouveau period in the late 19th century.

Throughout the 20th century, new mass production techniques led to the widespread availability of glass in much larger amounts, making it practical as a building material and enabling new applications of glass. In the 1920s, a mold-edged process was developed, in which art was etched directly into the mold so that each cast piece emerged from the mold with the image already on the surface of a glass. This reduced manufacturing costs and combined with a wider use of colored glass

led to cheap glassware in the 1930s, which later became known as depression glass. In the 1950s, Pilkington Brothers, England, developed the float glass process, producing high-quality distortion-free flat sheets of glass by floating in molten tin. Modern multi-story buildings are frequently constructed with curtain walls made almost entirely of glass.

Laminated glass has been widely applied to vehicles for windscreens. Optical glass for spectacles has been used since the Middle Ages. The production of lenses has become increasingly proficient. aiding astronomers, as well as having other applications in medicine and science. Glass is also employed as the aperture cover in many solar energy collectors. In the 21st century, glass manufacturers had developed different brands of chemically strengthened glass for widespread application and touchscreens, for smartphones, tablet computers,

and many other types of information appliances. These include Gorilla Glass, developed and manufactured by Corning, AGC Inks Dragon Trail, and Shot AG's Sensation. Glass is in widespread use in optical systems, due to its ability to refract, reflect, and transmit light following geometrical optics. The most common and oldest applications of glass and optics are lenses, windows, mirrors, and prisms.

The key optical properties refractive index, dispersion, and transmission of glass are strongly dependent on chemical composition, and to a lesser degree, its thermal history. Optical glass typically has a refractive index of 1.4 to 2.4, and an oboe number, which characterizes dispersion of 15. 100. The refractive index may be modified by high-density refractive index increases or low-density refractive index decreases additives. Glass transparency results from the absence of grain boundaries, which diffusely scatter light in polycrystalline materials. Semi-opacity due to crystallization may be be induced in many glasses by maintaining them for a long period at a temperature just insufficient to cause fusion. In this way, the crystalline divitrified material known as Raymmer's glass porcelain is produced. Although generally transparent to visible light, glasses may be opaque to other

wavelengths of light. While silicate glasses are generally opaque to infrared wavelengths, with a transmission cutoff at 4 microns, heavy metal fluoride and calcogenide glasses are transparent to infrared wavelengths of 7 to 18 microns. The addition of metallic oxides results in different colored glasses, as the metallic ions will absorb wavelengths of light, corresponding to specific colors. In the manufacturing process, glasses can be poured, formed, extruded, and molded, and deforms ranging from flat sheets to highly intricate shapes. The finished product is brittle, but can be laminated or tempered to enhance durability. Glass is typically inert, resistant to chemical attack,

and can mostly withstand the action of water, making it an ideal material for the manufacture of containers for foodstuffs and most chemicals. Nevertheless, although usually highly resistant to chemical attack, Glass will corrode or dissolve under some conditions. The materials that make up a particular glass composition affect how quickly the glass corrods. Glasses containing a high proportion of alkali or alkaline earth elements are more susceptible to corrosion than other glass compositions.

The density of glass varies with chemical composition, with values ranging from 2.2 grams per cubic centimeter for fused silica to 7.2 grams per cubic centimeter for dense flint glass. Glass is stronger than most metals, with a theoretical tensile strength for pure flawless glass, estimated at 14 to 35 gigapescal, which is equivalent to 2 million to 5.1 million pounds per square inch due to its ability to undergo reversible compression without fracture.

However, the presence of scratches, bubbles, and other microscopic flaws lead to a typical range of 14 to 175 megapascals, or 2,000 to 25,400 PSI in most commercial glasses. Several processes, such as toughening, can increase the strength of glass. Carefully drawn flawless glass fibers can be produced with a strength of up to 11.5 gigapascals. The observation that old windows are sometimes found to be thicker at the bottom, than at the top, is often offered as supporting evidence for the view that glass flows over a time scale of centuries, the assumption being that the glass has exhibited the liquid property

of flowing from one shape to another. This assumption is incorrect, as once solidified, glass stops flowing. The sags and ripples observed in old glass were already there the day it was made. Manufacturing processes used in the past produced sheets with imperfect surfaces and non-uniform thickness. The near-perfect float glass used today

only became widespread in the 1960s. A 2017 study computed the rate of flow of the medieval glass used in Westminster Abbey from the year 1268. The study found that the room temperature viscosity of this glass was roughly 10 to the 24th Pascals, which is about 10 to the 16th times less viscous than a previous estimate made in 1998, which focused on Soto-Lyme-Silicate Glass. Even with this lower viscosity, the study authors calculated that the maximum flow rate of medieval glass

is one nanometer per billion years, making it impossible to observe in a human time scale. Silicon dioxide is a common fundamental constituent of glass. Fused quartz is a glass made from chemically pure silica. It has very low thermal expansion and excellent resistance to thermal shock. Being able to survive immersion in water while red-hot, resists high temperatures and chemical weathering, and is very hard. It is also transparent to a wider spectral range than ordinary glass.

extending from the visible further into both the UV and IR ranges, and is sometimes used where transparency to these wavelengths is necessary. Fused quartz is used for high temperature applications, such as furnace tubes, lighting tubes, melting crucibles, etc. However, its high melting temperature, 1,723,000,000,000. degrees Celsius and viscosity make it difficult to work with. Therefore, normally other substances flexes are added to lower the melting temperature and simplify gas processing. Sodium carbonate is a common additive and acts to lower the glass transition temperature. However, sodium silicate is water

soluble, so lime, calcium oxide, generally obtained from limestone, along with magnesium oxide, and aluminum oxide, are commonly added to improve chemical durability. Soda lime glasses plus lime plus magnesium plus alumina account for over 75% of manufactured glass, containing about 70 to 74% silica by weight. Soda lime silicate glass is transparent, easily formed, and most suitable for window glass and tableware. However, it has a high thermal expansion and poor resistance to heat. Soda lime glass is typically used for windows, bottles, light bulbs, and jars. Borosilicate glasses, e.g. Pyrex, Turin, typically contain 5 to 13% boron trioxide. Borosilicate glasses have fairly low coefficients of thermal expansion. They are therefore less subject to stress caused by thermal

expansion and thus less vulnerable to cracking from thermal shock. They are commonly used for labware, household cookware, and sealed-beam carhead lamps. The addition of lead oxide into silicate glass lowers the melting point and viscosity of the melt. The high density of lead glass results in a high electron density and hence high refractive index, making the look of glass wear more brilliant and causing noticeably more specular reflection

and increased optical dispersion. Lead glass has a high elasticity, making the glass wear more workable and giving rise to a clear ring sound when struck. However, lead glass cannot withstand high temperatures well. Lead oxide also facilitates the solubility of other metal oxides and is used in colored glass. The viscosity decrease of lead glass melt

is very significant, roughly 100 times in comparison with soda glass. This allows easier removal of bubbles and working at lower temperatures ends its frequent use as an additive in vitreous enamel and glass sodders.