Architectural Glass: What It Is and How It’s Evolved
Architectural glass is glass used in buildings. Most of the time, it’s the clear stuff you see in windows and exterior walls. But it’s not just for the outside. You’ll also find it inside, dividing rooms or used as a design feature. In buildings, glass usually needs to be strong and safe. So it's often reinforced, toughened, or laminated to keep it from breaking easily.
How Architectural Glass Has Changed Over Time
Back in 1226, a type called “Broad Sheet” was first made in Sussex. By 1330, people in Rouen, France were making “Crown glass” for things like art and vessels. They also kept producing Broad Sheet. Both kinds were sent out for trade too.
In the 1500s, glassmakers in Venice figured out how to make mirrors. They did it on the island of Murano by covering the back of plate glass with a mercury and tin mix. This gave a clean, accurate reflection, which was new at the time.
In the 1620s, “Blown plate” glass showed up in London. It was used for mirrors and coach windows. Then in 1678, Crown glass was produced in London for the first time. This method stayed popular until the 1800s.
By 1843, Henry Bessemer came up with an early version of float glass. He poured molten glass onto liquid tin. It was a clever idea but too costly to take off commercially.
Tempered glass came in 1874. A French inventor named Francois Royer de la Bastie made it by cooling hot glass in oil or grease. This made it much tougher than regular glass.
In 1888, machines started rolling glass with patterns, opening the door to decorative styles.
Then in 1898, Pilkington made the first wired-cast glass. It added safety and security by holding together even when it broke.
Finally, in 1959, float glass as we know it today was launched in the UK. It was invented by Sir Alastair Pilkington and became the standard for smooth, clear panes.
What Is Cast Glass and How It’s Made
Cast glass is made by pouring molten glass into a mould. Once it cools and hardens, it takes the shape of the mould. This method goes way back to ancient Egypt. Today, there are a few different ways to cast glass. Some use kilns. Others pour into sand, graphite, or metal moulds.
In ancient Rome, cast glass was used in important buildings and fancy homes, like the villas in Herculaneum and Pompeii. The quality wasn’t great for seeing through, but it did the job and added a unique look.
Crown Glass: One of the Oldest Flat Glass Methods
Crown glass was one of the first ways people made flat glass for windows. The process started by blowing molten glass into a bubble. Then, while the glass was still hot, workers cut it open on the side opposite the pipe and spun it fast on a table. The spinning used centrifugal force to spread the glass into a round, flat sheet.
After shaping it, they’d snap it off the pipe and trim it to fit into a rectangular frame. The center of the sheet kept a thick bump where the pipe had been. That bump was called the "bullseye." It often distorted the view through the glass. To fix that, they sometimes ground the glass surface to reduce the distortion.
One reason diamond-shaped panes became common in old window designs was that you could easily cut three regular diamonds from one sheet of crown glass. It saved glass and kept distortions minimal.
Crown glass was expensive and couldn’t be made in large sizes. That’s why it was eventually replaced in the 1800s by cylinder, sheet, and rolled plate methods. Still, crown glass is sometimes used today in traditional buildings and historic restorations.
Cylinder Glass: A Step Toward Flat Glass
The cylinder process started with blowing glass into a long iron mould shaped like a tube. After forming the cylinder, they’d cut off both ends. Then they’d slice down one side of the tube.
That open cylinder was reheated in an oven. Once it softened, it would unroll and flatten out into a sheet. This method gave a larger pane than crown glass and was a key improvement in glassmaking.
Drawn Sheet Glass: The Fourcault Method
Drawn sheet glass was made using a process called the Fourcault method. It worked by dipping a starter rod or leader into a vat of molten glass. The leader was pulled straight up, and a thin film of glass came with it. As that glass cooled, it hardened into a vertical ribbon.
Tractors pulled the glass up by both edges to keep it straight. Once about 12 meters were drawn, the glass was cut off the ribbon and tipped over for further cutting.
This glass looked clear, but temperature changes during cooling caused small thickness differences. That led to faint distortion lines in the glass. You can still spot these lines in older homes today.
Irving Wightman Colburn came up with a similar method on his own. He started experimenting in 1899 and began production by 1906. The early versions had flaws, and he eventually went bankrupt. But Michael Joseph Owens bought the rights, kept refining the process, and finally opened a working factory in 1917.
Cast Plate Glass: Hartley’s Rolled Plate Innovation
In 1838, James Hartley patented a way to make rolled plate glass using a casting method. Here’s how it worked.
Glass was scooped out of the furnace using large iron ladles, suspended on overhead rails. The molten glass was dumped onto a flat cast-iron table. Then, a heavy roller spread it out into a sheet, kind of like rolling out dough. This was similar to how plate glass was made, but at a smaller scale.
While the sheet was still hot, workers trimmed off the rough edges. These edges were the parts that had touched the ladle and usually got ruined. After trimming, the soft sheet went into a long heated tunnel called a lehr. The lehr controlled the cooling, helping the glass harden without cracking. Rollers pushed the sheet slowly through the tunnel until it cooled down fully.
Polished Plate Glass: From Distorted Sheets to Smooth Mirrors
Polished plate glass starts off as rough sheet or rolled glass. This early version isn’t flat and often looks warped. You’d get weird visual distortions when looking through it, kind of like funhouse mirrors. To fix that, the glass would be ground down to flatten it, then polished to make it clear. But doing all that took time and money.
Before float glass came along, mirrors had to be made from plate glass. Sheet glass just wasn’t clear or accurate enough.
In 1918, a Belgian engineer named Emil Bicheroux came up with a better method. He poured molten glass between two rollers, which made the thickness more even and got rid of a lot of the waves and ripples. That meant less polishing and less waste. Later, the process got refined even more in the United States.
Rolled Plate Glass: How Figured or ‘Cathedral’ Glass Is Made
Figured glass, sometimes called cathedral glass, is made with a version of the rolled plate glass method. The difference is that the rollers used to shape it carry a pattern. Sometimes both rollers are patterned, but usually it’s just one. As the hot glass passes through, the roller stamps a raised design into the surface. A printing roller can also press into the sheet right after it comes through the rollers while the glass is still soft. That’s what creates the bold, high-relief look.
After that, the glass is cooled slowly in a long oven called a lehr to relieve internal stress.
This type of glass is usually whiter than regular clear glass. The cleaner tone helps the pattern stand out more.
Whether this kind of glass can be made into safety glass depends on the pattern’s depth. If the design is shallow and only on one side, the glass can sometimes be laminated to improve safety. But when patterns are on both sides, it’s called double rolled figured glass. That kind can’t be turned into safety glass because of the raised texture on both faces. It’s usually made thicker to handle that dual embossing. How thick it ends up depends on how deep the design is pressed in.
Float Glass: The Standard for Flat Glass Today
Float glass is how most flat glass is made now. About 90 percent of it, in fact. This method was invented in the 1950s by Sir Alastair Pilkington of Pilkington Glass.
Here’s how it works. Molten glass is poured onto a bath of molten tin. The glass floats on the surface and spreads out until it’s flat and level. Both sides come out smooth. As it moves along the bath, the glass cools and hardens into a ribbon. Then it goes into a lehr, an oven that slowly cools the glass down and removes internal stress.
The result is glass with almost perfectly even surfaces. But the side that touches the tin picks up a tiny bit of it. That side is slightly softer and easier to scratch. On the flip side, it also makes it easier to coat, which is helpful when turning the glass into a mirror.
Float glass is made in standard metric thicknesses. Common sizes are 2, 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 millimeters. Out of all those, 10 mm is the most used in architecture.
Left alone, molten glass on the tin spreads out naturally to about 6 mm thick. That’s due to surface tension. To get it thinner, the glass has to be stretched as it floats and cools. To make it thicker, the flow is slowed down or pushed back while it’s still over the tin.
Toughened Glass: How It Works and Why It's Safer
Toughened glass, also called tempered glass, starts off as regular float glass. But it goes through a special process that makes it much stronger and safer. If you break a standard float glass pane, it snaps into sharp, dangerous shards. Toughened glass, on the other hand, breaks into small, dull pieces that are far less likely to hurt you.
The process begins once the glass is cut into shape. The panels go into a toughening furnace, where they’re heated to over 600 degrees Celsius. Right after that, cold air hits the surfaces fast, cooling them down quickly. This rapid cooling creates tension between the inside and the surface. The outside hardens first while the inside is still hot. As the surface shrinks, it pulls on the softer inside, building up stress in the glass.
These stresses are what make the glass so strong. It can take a much harder hit than regular glass. And if it does break, the pieces won’t be sharp or jagged.
Prism Glass: Bending Light to Brighten Dark Spaces
Prism glass is made to bend and spread light. Around the early 1900s, it was often used to bring daylight into places that didn’t have direct window access. Think basements, shops below street level, or rooms tucked far from the building’s exterior walls.
One common use was vault lighting, where prism glass tiles were set into sidewalks to light the rooms below. In buildings, you’d find prism tiles in windows, canopies, and partitions. On old sailing ships, deck prisms brought sunlight into the lower decks. These tiles weren’t just practical either. Some were highly decorative. Frank Lloyd Wright even designed over forty different styles.
Today, you don’t see glass prisms used as much in buildings. Instead, many modern designs use clear window glass with a thin plastic film to get that same light-bending effect.
Glass Block: Letting in Light Without Giving Up Privacy
Glass block, also called glass brick, is used when you want light but still need some privacy. It lets natural light pass through, but the view is distorted. That makes it great for spots like public bathrooms, underground garages, and pool buildings where you don’t want people to see in clearly.
Glass block came onto the scene in the early 1900s. Back then, it helped brighten up industrial buildings. Factories got daylight without giving up security or privacy. That same idea still holds today.
Annealed Glass: Why It’s Not Safe for All Uses
Annealed glass is regular glass that’s cooled down slowly during production. This slow cooling removes internal stresses. It doesn’t go through extra heat treatment like toughened glass does. Float glass is already annealed when it’s made, but toughened glass takes that float glass and heats it again for added strength.
The downside to annealed glass is how it breaks. When it shatters, the pieces are big and jagged. That makes it dangerous in certain settings. Because of that, building codes in many places limit where you can use it. In areas where glass could easily break and hurt someone (like bathrooms, doors, fire exits, or low windows in homes and schools), it’s usually not allowed.
In those spots, safety glass is required. That means laminated or tempered glass, which doesn’t break into dangerous shards. It helps reduce the risk of cuts or serious injuries if the glass ever fails.
Laminated Glass: How It’s Made and Where It’s Used
Laminated glass is made by pressing two or more sheets of glass together with a layer of plastic in between. That plastic layer, usually PVB, sticks to the glass using heat and pressure. The result is one solid piece. If the glass breaks, the plastic holds it together so it doesn’t fall apart. That inner layer also helps block out sound, so laminated glass can be good for noise control too.
There are different kinds of laminated glass. The type of glass used and the kind of interlayer both affect how the glass acts when it breaks.
Laminated glass made from regular annealed glass is common where safety matters, but where you can’t use tempered glass. Car windshields are a good example. If a rock hits the windshield and it cracks, the PVB holds the glass in place. You’ll usually see a “spider web” pattern where it breaks, but the glass doesn’t fall apart.
Tempered laminated glass is made to break into tiny pieces to help reduce injuries. If both glass layers shatter, it creates a soft, drooping effect. The whole piece can fall from the frame, kind of like a heavy wet blanket.
Heat-strengthened laminated glass is tougher than annealed but not as strong as fully tempered glass. It’s often used for security purposes. When it breaks, it doesn’t collapse like tempered glass. It stays in place and can take more hits over a longer time, which makes it harder to get through.
Laminated glass and ballistic glass may sound similar, but they’re not the same. Both use a PVB layer, but ballistic glass is much stronger. Each one meets different safety standards and breaks in different ways.
Heat-Strengthened Glass: What It Is and How It Breaks
Heat-strengthened glass is made by heating glass and then cooling it quickly to build up pressure on the surface. This makes it stronger than regular glass, but not as strong as tempered glass. When it breaks, it doesn’t shatter into tiny pieces like tempered glass does. It cracks into sharp chunks that are smaller than what you'd see from broken annealed glass.
This type of glass can handle a solid hit to the face without breaking. But the edges are weak. If you hit the edge with something hard, the whole pane can break. So while it’s stronger in the middle, you still have to be careful around the sides.
Chemically Strengthened Glass: What It Is and How It Works
Chemically strengthened glass is made to be much stronger than standard glass. But when it breaks, it still shatters into long, sharp pieces like regular float glass. That means it doesn’t count as safety glass. If safety is a must, it has to be laminated. This type of glass is about six to eight times stronger than basic annealed glass.
The strengthening process involves dipping the glass into a hot bath filled with potassium salt, usually potassium nitrate, at around 450 degrees Celsius. In this bath, the smaller sodium ions on the surface of the glass get swapped out with larger potassium ions. That change builds pressure at the surface, which makes the glass much tougher.
One big difference between this and toughened glass is that chemically strengthened glass can still be cut after the treatment. But there’s a catch. If you cut it, the strength around the cut drops off within about 20 millimeters. Deep scratches also weaken those areas and cancel out the extra strength.
This type of glass has been used in certain military aircraft canopies, where strong but optically clear material was needed.
Low-Emissivity Glass: How It Saves Energy
Low-emissivity glass has a special coating that reflects infrared heat but lets visible light pass through. That coating helps keep radiant heat where it started. So, in the winter, heat from inside your home gets reflected back in. In the summer, it blocks heat from the sun, keeping the inside cooler.
This kind of glass makes windows more efficient. It helps with heating in cold months and cuts down on cooling during hot months. That’s why it’s used a lot in modern buildings that aim to save energy.
Heatable Glass: Warmth Built Right In
Heatable glass is a newer product used in both buildings and vehicles. The basic idea is simple. You take energy-efficient glass, usually low-emissivity silicate glass, and coat it with thin layers of metallic oxides. Then it can be powered to produce heat.
You can use this glass in almost any standard frame, whether it’s wood, plastic, aluminum, or steel. It opens up new options for design, especially in cold climates or in places where keeping windows free of fog or ice is important.
Self-Cleaning Glass: How It Keeps Itself Clear
Self-cleaning glass came onto the scene in 2001, developed by Pilkington Glass. It was designed for buildings, cars, and other technical uses. The secret is a very thin layer of titanium dioxide on the outer surface of the glass. This coating does two things.
First, it reacts with sunlight. UV rays help break down organic dirt and grime on the surface. Second, the coating attracts water. Instead of forming droplets, water spreads into a thin sheet that washes away the loosened dirt. So when it rains, the glass basically cleans itself.
Insulating Glass: Double Glazing That Works
Insulating glass, also called double glazing, has two or more glass layers with a sealed gap in between. There’s a spacer along the edge that keeps the layers apart and creates a pocket of air or gas.
This space helps in two ways. It keeps heat from escaping and also cuts down on outside noise. If that gap is filled with inert gas, like argon, it makes the insulation even better.
That’s why insulating glass is used in energy-saving buildings and low-energy architectural designs. It’s a key part of keeping indoor temperatures stable without using too much power.
Evacuated Glazing: How It Works and Where It Fits
Evacuated glazing is a newer form of insulated glass. It came out in 1994 but is still mainly produced in Japan and China. The main draw is its thin profile. This makes it a good option for older buildings or projects where keeping the original look matters. It’s much more energy-efficient than traditional single-pane windows, so it’s a solid upgrade without changing the visual style too much.
To make an evacuated glazing unit, two sheets of glass are sealed together at the edges. Usually, a type of solder glass is used for this. Then the air between the sheets gets sucked out with a vacuum pump. Even though the gap between the glass layers is very small, the vacuum makes it a great insulator. That’s because no air means no convection or heat transfer through gas. So you get solid insulation in a unit that’s only about 6 mm thick overall.
The process sounds simple, but it’s not. Making evacuated glazing is tough. One key step is called outgassing. This means heating the glass to release any trapped gases on the inside surfaces. If this step is skipped or done wrong, those gases can leak out later and ruin the vacuum seal. But here’s the problem: this heating stage means the glass can’t be toughened or heat-strengthened. So if safety glass is needed, the glass has to be laminated instead.
That same high heat also messes with modern coatings. Most insulated glass uses low-emissivity coatings on the inside surfaces to reflect heat and cut down on infrared heat loss. These "soft" coatings don’t survive the outgassing step. So with evacuated glazing, you have to use "hard" coatings instead. They’re more durable but not as good at reducing heat loss.
There’s also a structural issue. Since there’s a vacuum between the glass sheets, outside air pressure pushes on the glass. Without support, the sheets could bend and touch. That would ruin the insulation. To prevent this, tiny spacers are added between the panes. These are usually small stainless steel discs spaced about 20 mm apart. They’re not easy to spot unless you’re standing really close, maybe within a meter.
But those spacers conduct heat. In cold weather, they can cause little circular patterns to form on the glass. Inside, it might show up as condensation rings around each spacer. Outside, if there’s dew, you might see dry spots where the spacers keep the glass slightly warmer.
Because of the heat transfer through the spacers, the overall insulation isn't perfect. Still, evacuated glazing holds up well compared to much thicker double glazing. And because the glass sheets are pressed together by air pressure, they act like a single thicker sheet. This makes them more resistant to bending and even better at blocking sound.
Heat Reduction Glass: How It Lowers Cooling Costs
Heat reduction glass is designed to keep buildings cooler by blocking heat. One version does this using radiative cooling. It works by letting visible light through while pushing heat away from the surface. This can bring down cooling costs by up to a third.
Here’s how it’s made. A thin layer, just 1.2 microns thick, sits on top of the glass. This layer is called a transparent radiative cooler, or TRC. It’s made from silica, alumina, and titanium oxide. Underneath, the glass is coated with the same polymer used in contact lenses. The TRC only allows visible light to pass through but reflects infrared heat. That’s what helps reduce indoor temperatures.
The design process wasn’t trial and error. The team behind it used machine learning and quantum computing to test a lot of options fast. This helped them find the right mix of materials and structure without wasting time or resources.
