Glass Sleep Facts

If you’re looking for a relaxing deep dive into something both fragile and oddly durable, this episode about glass should do the trick. From its sleepy silicate beginnings to its many transparent moods, there’s plenty here to lull your brain into a gentle stupor. Perfect for fans of insomnia relief, bedtime stories, and long, slow explanations of materials you never think about.

Transcript

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-crystalline solid,

Because it is often transparent and chemically inert.

Glass has found widespread practical,

Technological,

And decorative use in windowpanes,

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 3600 BC in Mesopotamia,

Egypt,

Or Syria.

The earliest known glass objects were beads,

Perhaps created accidentally during metalworking,

Or the production of faience,

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 manufactured 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.

Extruded 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-crystalline 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 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 17th to 10 to the 18th pascals 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 adiatic 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 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 where 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 moldivite 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 fulgurides.

Trinitide is a glassy residue formed from the desert floor sand at the Trinity nuclear bomb test site.

Etioi glass found in South Australia is proposed to originate from Pleistocene grassland fires,

Lightning strikes,

Or hypervelocity impact by one or several asteroids or comets.

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.

Glass making 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 in the coastal north Syria,

Mesopotamia,

Or ancient Egypt.

The earliest known glass objects of the mid-3rd millennium BC 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.

Early glass was rarely transparent and often contained impurities and imperfections,

And is technically faience rather than true glass,

Which did not appear until 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 stone-working,

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 Týr,

Located in current-day Germany,

Where the late Latin term glaesum 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-glass windows of churches,

And cathedrals,

With famous examples as Chartres Cathedral and the Basilica of Saint Denis.

By the 14th century,

Architects were designing buildings with walls of stained glass,

Such as Saint-Chapelle,

Paris,

1203-1248,

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 in 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,

Ship's 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-etch 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 the 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 in touchscreens,

For smartphones,

Tablet computers,

And many other types of information appliances.

These include Gorilla Glass,

Developed and manufactured by Corning,

AGC Inc.

's Dragon Trail,

And Schott 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 in 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 Abbe number,

Which characterizes dispersion,

Of 15 to 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 induced in many glasses by maintaining them for a long period at a temperature just insufficient to cause fusion.

In this way,

The crystalline,

Vitrified material,

Known as Raymer'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 cut-off at 4 microns,

Heavy metal fluoride and chalcogenide 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 into forms 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 corrodes.

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.

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 gigapascals,

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 stuffing,

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 timescale 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 sodalime silica 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 timescale.

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 degrees Celsius,

And viscosity make it difficult to work with.

Therefore,

Normally other substances,

Fluxes,

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.

Sodalime glasses plus lime plus magnesia plus alumina account for over 75% of manufactured glass,

Containing about 70 to 74% silica by weight.

Sodalime 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.

Sodalime 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 car headlamps.

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 glassware more brilliant and causing noticeably more specular reflection and increased optical dispersion.

Lead glass has a high elasticity,

Making the glassware 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,

Hence its frequent use as an additive in vitreous enamels and glass solders.

Reviews

I will never look at glass the same way again, Benjamin! Next time I'll try to stay awake more than a few minutes. 😆Thank you!

Here's to glass! 🔎🥛🥂👓🤓

Hearing this gives me a new appreciation for this everyday, ubiquitous substance that I totally overlook and take for granted. But it's been with humanity for many millennia and it's both beautiful and utilitarian.

I really love your readings! They are by far my favorite thing on Insight Timer. I've been falling asleep to these for years now. And also learning. These little readings inspire my curiosity about the world we live in, and encourage me to maintain that childlike sense of wonder at all the interesting and amazing people, places and things in this vast, wild universe. All that while, paradoxically, indeed boring me right into the world of sleep 😴

Thank you so much Benjamin! Kind greetings from Germany
😊🦋💖✨

My ears perked up when I heard "Murano Glass". I was just there recently for my 2nd time, I love it. Burano too. Thank you once again, Benjamin.