The Origins of Glass Making

Natural glass has existed for a long time. Glass can appear naturally in nature, like the glass made by volcanoes called obsidian. Humans have used this type of glass for many purposes, including weapons and jewelry. Lighting strikes also create a kind of glass called fulgurites, which are quite beautiful to behold. 

It is believed that the Egyptians around 2500 B.C made the earliest known human-made glass objects. First, the Egyptians designed non-transparent glass beads. This eventually led them to create glass pots. These pots were made by dipping molded and compacted sand into molten glass. The mold was turned, causing the sand to mold to adhere to the molten glass.  Then it was rolled on a stone slab while still soft and malleable. 

Around the first century B.C., there was a significant leap forward in glassmaking when the Syrians introduced glass blowing. By using a long thin metal tube and inserting it into molten glass, the Syrians created the first blow glass objects. It was inserted into molten glass and removed. Then artisans would blow into the tube, giving a hollow shape to the glass. Sometime after that, the ancient Romans began blowing glass inside of molds, significantly increasing the variety of forms for hollow glass items. Amazingly, these methods are still used by glassmakers today. Simultaneously, the Romans started to utilize glass for architectural purposes, although the windows were thick cast blocks and weren’t very clear. As the Roman Empire expanded, so too did their skill of glass making.

In the middle ages, the Italian city of Venice became the leader in glass production. The Venetians experimented with different raw materials, like crystal, to create a more transparent glass type. The Italians did not want their craftsmen or technology to be duplicated. Hence, they forced the glassmakers to work and reside on Murano Island, enabling the Venetians to ensure that no trade secrets were exported. The Venetians were also at the forefront of using glass to make trade beads. These glass beads were used as currency and are still valued today.

In 1674 clearer lead crystals were developed by an Englishman, George Ravenscroft. Ravenscroft was able to find an alternative to the highly prized Venetian crystal, composed of pure quartz sand and potash. By changing the ratio of lead oxide to potash, he produced a sparkling glass with high reflectivity. Because of the high lead count, this softer glass was well suited for deep cutting and engraving.

Another major development in glass production happened in France in the late 1600s. The French invented a new process for the manufacturing of plate glass. The molten glass was poured onto a unique table and rolled out flat. After cooling, the plate glass was ground on large round tables utilizing rotating cast-iron discs. Fine abrasive sands were used to grind surface imperfections from the plate surface. Subsequently, the plates were polished using felt discs. The result was flat glass with superior optical qualities, which became an industry standard at the time. Known globally as French panes, this term is still used in the industry today to describe multiple small windows in a single frame. Besides being suitable architectural glass, these plates were also coated on one side with a reflective low melting point metal to create high-quality mirrors.

It wasn’t until the latter stages of the industrial revolution that mechanical technology led to glass’s mass production. Glass blowing machines, automated rollers, and tank furnaces all saw their debut during this period. Simultaneously, scientific research was being conducted to figure out the relationship between glass composition and its inherent physical properties.

The glass manufacturers were funding this research in a quest to improve and diversify their product offerings. In France, Edward Benedictus started strengthening glass through lamination, a celluloid material layer sandwiched between two glass sheets. He patented this process in 1910 under the name “Triplex.”

The last significant advancement in flat glass’s mass production was the float process developed after the second world war by Britain’s Pilkington Brothers Ltd. Introduced in 1959, it enabled manufacturers to combine the brilliant finish of sheet glass with plate glass’s optical properties. Molten glass is poured across a bath of molten tin. There it’s spread and flattened before being drawn into an annealing lehr oven where it is cooled at varying rates. By changing the cooling temperatures, manufacturers can alter the strength of the glass. This is the primary method of glass production in use today.

Types of Glass

As discussed in the History of Glass section, the amount of heat used in the glass manufacturing process affects the type of glass produced. The more heat used during the glass production process, the stronger the final glass product will be. The following provides a breakdown of different glass types, starting with the lowest amount of heat used (Annealed) and working up to the hottest method (Tempered).

Annealed Glass – This is the most common type of glass used today and used in most home windows. Using the float method of manufacturing, molten glass is poured continuously onto a bed of molten tin. Because the tin’s melting point is less than glass, the glass solidifies as it cools on top of the tin. Increasing or decreasing the rate of molten glass flow onto the tin can control thickness levels. Once the glass becomes solid, it is then cooled in an annealing oven to remove any residual stress. Annealed glass is the most fragile type of manufactured glass because of the relatively low amount of surface heat compression. When glass breakage occurs, it does so in many small and irregularly shaped pieces.

Heat-Treated Glass – Heat-Treated Glass is twice as strong as annealed glass. This process takes the annealed glass and heats it to its softening point (1200 degrees F), controlled, and cooled using water. Water cools the glass’s surface quicker than the interior glass, thus providing an extra degree of surface compression. An increase in the rate of cooling will result in a more substantial surface compression. Heat Treated glass is stronger than standard annealed glass and is more resistant to stress caused by heat, wind, and flying objects (but not as strong as safety glazing products).

Thermally Tempered Glass – When the heat-treatment method is increased to provide the highest amount of surface compression, the result is Thermally Tempered Glass (TTG). This glass type is four times as strong as annealed glass and is very resistant to thermal temperature changes that cause cracking. When tempered glass is broken, it breaks into smaller pieces (shards) that are less dangerous than larger fragments created by the annealed glass. Tempered glass is beneficial to glass breakage areas, such as car windshields and commercial storefronts. An etching label is generally on the corner of most tempered glass. This is to ensure that the glass is fully tempered.

Laminated Glass - Any one of the above types of glass can be laminated. The most commonly used finished product is two sheets of toughened glass, laminated together with a 1.52mm thick Polyvinyl Butyral (PVB) interlayer.

Laminated glass offers many advantages. Safety and security are the best known of these, so rather than shattering on impact, laminated glass is held together by the interlayer. This reduces the safety hazard associated with shattered glass fragments and, to some degree, the security risks associated with easy penetration.

You can read more about laminated glass in the section below.

Types of Glass Construction

There are three types of glass construction:

1. Monolithic Glass – Monolithic glass is the most basic form of glass. It is a single piece of glass constructed using one glass thickness. Monolithic glass is created using one of 3 methods: annealed, heat-treated, or tempered glass float.
2. Laminated Glass – Laminated glass is made by combining two panes of glass fused with a middle layer of Polyvinyl Butylenes Film (PVB). PVB behaves like a bonding agent to hold broken glass in place. This feature creates a significant deterrent against forced entry and reduces the chances of flying pieces of broken glass. Car windshields and buildings/homes in hurricane-prone areas (e.g., Florida) often use laminated glass.

If a glass panel breaks or shatters, it is improbable that both laminated panels will break simultaneously, which means that the remaining panel and interlayer will support the broken glass and keep it in place as edge protection until it is replaced or secured suitably.

Another increasingly common interlayer is the SGP Interlayer (SPG stands for SentryGuard Plus Interlayer, crated by American brand Dupont). The product offers five times the tear strength and 100 times the rigidity of standard PVB. In the unlikely event of both panes of toughened glass failing, then the SGP will generally hold the glass in place. SGP offers an enhanced impact performance and greater protection against severe weather.

A variety of other interlayers are available which apply a range of different technologies to the application. Structural interlayers can be used to enhance the strength of the glass, where high loadings are required. Colored interlayers can be used for privacy or purely decorative purposes. Other properties, such as sound-dampening and fire resistance, can also be incorporated into the interlayer.

3. Insulated Glass – Insulated glass is used to describe two pieces of glass separated by airspace. Airspace is created using spacers or edge seals found at the top and bottom of an Insulated Glass (IG) unit. Additionally, a sealant is applied to the edge seals to absorb excess water vapor that moves across the seal. The airspace between the glass layers dramatically reduces heat transfer through conduction and convection. Heavy and inert gases like Argon and Krypton are sometimes added to the airspace to slow down convection and minimize heat transfer. As a window film installation company, we know that insulated glass units are highly susceptible to thermal stress fractures. This happens when improper films with high heat absorption (e.g., dyed films) are applied. This is why we only used approved window films based on the customer’s glass type.

There are a few different types of glass construction. This includes patterned, textured, and wired. It’s important to note that the aforementioned types of manufacturing processes usually create surface and edge flaws. This increases thermal stress, which is not the desired combination for window film applications. 

What about bullet-resistant glass? This thick glass is made using multiple laminates of glass and polycarbonates. The numerous layers increase the chance of thermal stress fractures. This is because they will heat and cool at varying temperatures. Therefore, solar control films are not recommended for bulletproof glass. A transparent film can be applied to the interior surface to hold glass shards together at impact to augment them.

Frame Types

The type of material used to construct a frame is critical. It’s used to measure the size, weight, and durability of a window. It also helps determine a window’s overall thermal performance.

There are 5 different types of window frame materials. Individual frame types include aluminum windows, composite windows, vinyl windows, fiberglass windows, and traditional wooden window frames. The window style, energy efficiency, and durability of each frame differ slightly. We will discuss the differences below.

Aluminum Frames – Aluminum frames are the most common frames used for residential windows. There are several reasons why aluminum frames are so popular. Aluminum is light and robust, making it easy to work with. It does not corrode and is generally a low-maintenance product. It’s an ideal metal for doors, including sliders, because of its durability and lightness. The one disadvantage of aluminum is that it's highly conductive and increases the U-value of a window. In colder climates, condensation problems can occur as frost or moisture builds up inside the frame. To minimize condensation and heat loss problems, aluminum frame manufacturers have developed better technologies utilizing “thermal breaks.”

Wood Frames – Long ago, wood frames were used because the material was readily available. With the emergence of new cost-effective frame technologies, wood frames are considered a high-end window frame purchase. Wood is very durable and lasts longer than other frame materials. Wood frames have a natural aesthetic appeal, and they blend in well with traditional home designs. However, wood frames are high maintenance products. They need unique treatments to reduce warping and prevent decay. As for thermal protection, wood frames perform well. The thicker the wood frame, the more heat insulation it provides.

Vinyl Frames – The vinyl frame market has grown quicker than any other framing material. Vinyl offers excellent insulating value and superb resistance to abrasion, corrosion, environmental pollutants, and insect pests like termites. It also maintains its original color since the color is part of the material. Similar to wood frames, vinyl frames provide strong heat insulation.

Hybrid Frames – Today, many window frames use a combination of materials. Wood frame manufacturers often utilize vinyl and aluminum clad materials to minimize maintenance. Similarly, vinyl frame producers sometimes use wood veneers to improve the overall look. New hybrid frames—including wood composites and fiberglass—are becoming popular as manufacturers look to enhance window frame strength, insulating value, and longevity.

Make Your Glass Better with ClimatePro

This comprehensive discussion of glass at least proves one thing: ClimatePro loves talking about glass, especially windows. We’ve been helping our San Francisco Bay Area neighbors to improve their glass windows for over 40 years. We believe that window film can make your windows. Try our Window Film Selector Tool to get a head start. Or you can contact us today for a free consultation and we’ll help you get started. We serve the entire San Francisco Bay Area. Reached us at 707-755-7337.