The silica, soda and lime are fused together at extremely high temperatures. By adding other substances during the process, the properties of the glass can be altered, including its color, how reflective it is, how brilliant or sparkling it looks, how well it acts as an insulator and more. Bits of old or broken glass from previous manufacturing, called ‘cullet’ is usually recycled into the mix. However, it is not just these additives alone that affect the final piece of glass, but also the way in which it is heated, cooled and formed.

First, the silica/soda/lime mixture is heated in melting furnaces to approximately 2,500° Fahrenheit, sometimes for as long as 24 hours. The molten glass is then cooled several hundred degrees, to a temperature at which it can be worked. At this stage the glass is an orange-red color and looks like a thick liquid. The glass has to be worked quickly to form it into the desired shape, because as the glass cools it becomes hard. The glass can now be blown, pressed, drawn or rolled. Finally, when the glass is formed into the desired shape, it is placed in a ‘lehr’ oven to be ‘annealed.’ This special process eliminates areas of stress in the glass to strengthen it, by cooling it down at controlled temperatures.

To blow glass, a blob of molten glass is placed at the end of a long, hollow iron blowpipe. Air is blown in and causes the glass to form into a pear-shaped bulb, which is then rolled on an oiled slab, shaped with tools and sometimes re-blown into a mold. To keep the glass from hardening during this process, it is periodically re-heated in small ovens. If the glass is to be engraved, copper wheels are used, and if it is to be etched, hydrofluoric acid does the job.

For glass bottles, a molten glass bubble is employed. It is placed in a mold, and the air pressure in the bubble forces the glass against the side of the mold. Once the glass cools and hardens, the mold is opened and a newly-made glass bottle removed.

Pressed glass, which offers better control of the glass’s density than blowing, was the first glass to be manufactured on a large scale with the invention of a glass-pressing machine in the U.S. in the 1920s. This worked by taking the molten glass from the furnace and dividing it up into small sections. These would be placed in molds made of iron or brass. A plunger would press the glass down into the mold, and after a few seconds it was ready.

Because the cold metal of the mold would produce wrinkles in the hot glass, intricate patterns were used to disguise the flaws. It wasn’t until twenty years later that a technique was developed to heat the molds to very high temperatures before dropping in the molten glass, which eliminated the wrinkles. The decorative patterns accordingly became simpler.

Drawn glass is the process used to manufacture tube and rod-shaped glass, as well as some sheet glass. To make tubes, the molten glass gets drawn over a hollow cylinder or cone that has air blowing through it, to keep it from collapsing until the glass hardens around it. The tube can be drawn out horizontally, vertically, or at an angle. Conversely, to make glass rods, the air inside the cylinder or cone is eliminated.

Rolled glass is used for some flat glass, and means that the sheet of glass rolls along the assembly line as it is manufactured. Because of the type of metal used in the rollers, they aren’t damaged by the heat of the molten glass. However, the glass can wind up with a rough surface. When this process was first developed, molten glass was poured onto large tables and then rolled flat onto plates. After it cooled, the glass was ground and polished.

Then a series of innovations began at the turn of the last century and continued through the first world war, improving the quality and economy of both drawn, sheet glass and rolled glass.

Float glass is the most widely used type of flat glass today. It was first developed after the second world war by a British company but not introduced to the market until they felt it was perfected, in 1959. Its manufacture is unique because the molten glass is formed by floating it on a bed of molten tin kept at high temperature. The glass spreads out and flattens, and is then drawn out into a continuous glass ribbon. The surface of the glass winds up being extremely smooth, with a brilliant finish like sheet glass, plus the optical quality of plate glass.

Cutting and drilling glass is a fine art. If the glass needs to be cut it must first be scored with a glass-cutter wheel. Pressure is then applied across the score to force a break. Another way to cut glass is thermally. This can be done with a focused flame heating a narrow strip of the glass. A water jet is then directed on the heated strip to break the glass. Or, a ring of focused flames are used to heat a particular area of the glass until it becomes soft enough to pull apart. Glass can be drilled, with either a steel drill, a tungsten-carbide drill, or for the best control, quality and speed of production, a diamond core drill.

Glass is categorized by its composition. The most common – ninety percent of manufactured glass – is so-called soda glass, the combination of silica, soda and lime. Although it’s the cheapest to make, it is also the least resistant to high temperature, or sudden changes in temperature, or chemicals.

Lead glass will usually have at least twenty percent lead oxide content. It looks brilliant in the light, especially when cut and faceted, and is more expensive that soda glass. But similar to soda glass, lead glass will also not do well with high temperature or sudden changes in temperature.

For better resistance to temperature changes and chemicals, the more expensive borosilicate glass is used. It has a minimum of 5% boric oxide, and is used to make light bulbs, sealed-beam headlights, bakeware and labware. And even more durable than borosilicate glass is aluminosilicate glass.

Fiberglass and foam glass are mostly used for insulation purposes. To make fiberglass, the molten glass is formed into continuous, hair-like glass filaments. Foam glass is made by trapping gas bubbles in the glass, creating an almost spongy consistency.

Colored glass is made by adding chemicals into the mix, with particular chemicals creating specific colors. For example, the amber or brown glass you see used in beer bottles gets its color from iron sulphide. Iron-chromite creates shades of green, while cobalt makes beautiful shades of blue.

Safety glass was first invented early in the 20th century by a French scientist. Today the process used is essentially the same, where two pieces of sheet or plate glass are bonded together with a layer in between them, which is usually plastic. This lamination keeps the glass from shattering and is why it is used for car windshields.

Conversely, tempered glass is found in the passenger and rear windows of a car, as well as many other applications. In the tempering process, the annealed glass is heated in a furnace past its ‘annealing point,’ then immediately cooled down with air jets. This forces the surface to quickly become cool and stiff, while the core of the glass, because it is still much hotter, takes longer to cool down and finally harden.

And that is what improves the strength of the tempered glass. If the surface receives any stress, it does not carry through to the core of the glass, so a crack is unable to form. If the glass does receive damage, it shatters into small cubes rather than sharp shards.

But not every smooth surface creates a reflection. That’s because some of these surfaces absorb the photons hitting them so they’re unable to bounce back. What’s more, when we do stand in front of a reflecting surface like a mirror, not all the photons that bounce off us will hit the mirror, because our bodies are rough objects themselves. But enough do bounce back that an image is formed, at exactly the same angle at which the photons hit the mirror. And keep in mind, the mirror image is actually backwards, as you can easily see if you stand in front of it holding a newspaper or magazine.

Mirrors are usually made of clear plate glass that has one side coated with a metal film to create the reflecting surface, called ‘silvering’. Where the surface and the glass meet is called the ‘mirror line.’ The most common type of mirror is the plane mirror, which has a flat surface. The rays of light that hit it are reflected back virtually unchanged, so the position of the image in the mirror is the same distance as the real object in front of it, and its size is the same size. You experience this every time you stand in front of the mirror in the bathroom – the closer you stand to the mirror, the closer your image appears in it.

Convex and concave mirrors – also known as ‘spherical mirrors’ – alter the look of the original object and the distance it appears to be in the mirror. A concave mirror (think of it as being ‘caved in’) has the mid-point of the reflecting surface farther away from the object in front of it than the edges. So the image that forms in a concave mirror depends on where it is in relation to the center of the mirror. It may be larger, smaller, or the same size. It may be upside down or right side up, and will be distorted from the real object.

Conversely, a convex mirror has the mid-point of the reflecting surface closer to the object than the edges, so the image that forms is consistently smaller than the real object in front of it, and standing upright. It will also be distorted. For example, drivers will stick a small convex mirror on their car or truck’s rear-view mirror to get a ‘bigger picture’ of what’s behind them than a regular, plane-type mirror shows.

Two-way mirrors are a special kind of mirror, usually used for observation and security purposes. They are sometimes also called one-way mirrors or see-through mirrors. You’ve probably seen them in action on tv shows or in movies where an interrogation is taking place. The perp is questioned in a room that has a mirror, while detectives observe him from behind the mirror in an adjoining room. So how come the criminal sees only his reflection but the cops see clear through the glass?

The answer is actually pretty simple. The two-way mirror in fact has only a very thin layer of reflective material applied to the glass. In fact, it’s so thin it’s referred to as being ‘half-silvered,’ as opposed to ‘silvered’ which is how you’d describe a regular mirror. So only half of the light that hits the mirror gets reflected, while the other half passes through it.

But with only half the reflecting power, you’d think the criminal would be able to see the detectives. The reason why he can’t is the way the two rooms are lit. If you watch the interrogation scene, you’ll notice the room with the criminal is brightly lit, so there is enough light to hit the mirror and reflect back his image. However, the room with the detectives is dark, so there’s not enough light to pass through that side of the glass back into the interrogation room.

Here’s another way to think of it: if the perp were to suddenly jump up and switch off the lights in the interrogation room, or if one of the cops accidentally turned on the lights in the observation room, the two-way mirror would act like a window, with everyone being able to see each other perfectly clearly.

Mirrors made of metal were the first to be made, mostly of flattened and highly polished copper and bronze. The reflecting surface would be on one side, and a design on the other, often with some kind of handle.

Bronze mirrors were made in China from Neolithic times (about 2000 B.C.) until the Qing dynasty, when Western mirrors were brought over. Although at first mirrors were not common, by the Han and Tang dynasties they were being mass produced and were more advanced. Always round, they featured intricate designs on the back and a knob in the center to attach to clothing.

These bronze mirrors made their way from China to Japan, where they were adapted to Japanese tastes. Called “shinju-kyo,” they featured gods and beasts as the design on the back.

Meanwhile, bronze mirrors were developed in Europe during the Bronze Age, with discoveries made in Britain, Greece and Italy. Specifically, Celtic mirrors were made in Britain until the Roman Conquest, and Etruscan mirrors were made from the 5th to 2nd centuries B.C. In ancient Rome mirrors were also made of tin, silver and gold.

Egypt also had bronze, and copper, mirrors. Formed from the molten metals, they were made into round, oval, or square shapes. But Egyptians also used the “natural glass,” obsidian, to make small mirrors as well, sometimes embedded directly into walls.

Mirrors made of glass had to wait until the discovery of glass making, and the Romans were the first to adapt this new technology. In fact, in Roman graves from the 2nd and 3rd centuries, mirror shards – pieces of glass covered with lead on one side – were found.

It took until the 14th century for glass blowing to be discovered, and this too was used in the production of mirrors. It began in a unique way: the mirrors were actually in glass bulbs. The glass blower would first blow the bulb, then pour a mixture of liquid metals like lead, tin and antimony down the pipe and into the bulb. Once cooled, the bulbs were cut open and the round ends, with the metal coating inside, became small convex mirrors. Although the reflection they would make wasn’t perfect, it was an improvement over bronze.

By the end of the Middle Ages this type of mirror production was improved further by using mercury mixed with tin, on a plate of flat glass, to create a larger, clearer reflection. While the invention of this process seems to have occurred in Germany and Belgium (then called Flanders), the artisans of Murano in Venice led the way in the production of these “mercury mirrors.” By the 16th century they were widespread. And because the exact components and process of making the mirrors was kept secret, the prices were able to be kept very high.

From what is understood, the production of mercury mirrors wasn’t easy. Not only was it complicated and time consuming, but to make matters worse, it was also unhealthy, as mercury fumes are very toxic.

And so the search was on to find a better way to make a mirror. It wasn’t until the 19th century that the “silver mirror” was developed. Although Germany seems the most likely place of its creation, England, France and Italy also claim the invention.

A simple description of the process is, to coat a glass surface with metallic silver. Specifically, aldehyde is mixed with a silver nitrite solution and heated. A reduction is formed, causing the silver to adhere on the glass surface.

MODERN MIRRORS

Today’smodern mirrors, including frameless mirrors, are made with a thin layer of molten silver, or aluminum, poured onto plate glass in a vacuum. For specialized mirrors, such as those in telescopes or other optical instruments, the aluminum is actually “evaporated” onto the front of the glass rather than the back to eliminate the possibility of reflections from the glass itself.

2. Why are your prices so low?
We import very large quantities of glass and purchase hundreds of one size at a time. We also sell glass tops in bulk to many large customers.

3. Does the glass need to be tempered?
The ½” and ¾” inch thick glass tops do not need to be tempered. We do however; recommend 1/4" and 3/8” thick glass tops to be tempered for extra strength. All of our 1/4" and 3/8” thick glass tops are tempered.

4. Why does glass appear green?
The greenish cast on glass tops comes from the minerals used in the manufacturing process. This is typical of all glass tops in the furniture industry, and is known as clear glass.

5. Do you have discounts for quantities of glass and lower shipping rates?
For large quantities of glass tops and lower shipping rates, please call our Sales Department at 800-850-6467, 9AM-5PM Eastern Time, Monday thru Friday, and of course you can email us with special requests.

6. Do you make sizes other than what is listed?
Yes, please submit your needs via email or fax.

7. What if my glass top is out of stock?
On rare occasions we may be out of stock on a particular size. If that is the case with your glass top, we will contact you with an estimated ship date.

8. Is it safe to buy from an Internet glass company?
Yes. Check what some of our customers are saying on our testimonial page.