Float Glass

In modern times, glass is manufactured by the float method. Float glass is a sheet of glass made by floating molten glass on a bed of molten tin. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass. Most float glass is soda-lime glass, but relatively minor quantities of specialty borosilicate and flat panel display glass are also produced using the float glass process. The float glass process is also known as the Pilkington process, since it was invented by Sir Alastair Pilkington in the 1950s.

Architectural Glass is by far one of the most awe-inspiring applications of this truly unique substance. Both in the interiors and the exteriors, the use of glass can enhance the look and feel of a construction like no other substance can. In recent times, architectural glass has adapted itself to changing requirements. Right from solar-control glass to self-cleaning glass, glass types can be selected like they were custom-made.

When used in buildings, glass is often of a safety type, which includes reinforced, toughened and laminated glasses.

Types of Architectural Glass

Crown Glass: One of the earliest methods of glass window manufacture was the crown glass method. Hot blown glass was cut open opposite the pipe, and then rapidly spun on a table before it could cool. Centrifugal force forced the hot globe of glass into a round, flat sheet. The sheet would then be broken off the pipe and trimmed to form a rectangular window to fit into a frame.
At the center of a piece of crown glass, a thick remnant of the original blown bottle neck would remain, hence the name "bullseye". Optical distortions produced by the bullseye could be reduced by grinding the glass. The development of diaper latticed windows was in part because three regular diamond-shaped panes could be conveniently cut from a piece of Crown glass, with minimum waste and with minimum distortion.

This method for manufacturing flat glass panels was very expensive and could not be used to make large panes. It was replaced in the 19th century by the cylinder, sheet and rolled plate processes, but it is still used in traditional construction and restoration.

Cylinder Glass: In this manufacturing process, glass is blown into a cylindrical iron mould. The ends are cut off and a cut is made down the side of the cylinder. The cut cylinder is then placed in an oven where the cylinder unrolls into a flat glass sheet.

Drawn Sheet Glass: Drawn sheet glass was made by dipping a leader into a vat of molten glass then pulling that leader straight up while a film of glass hardened just out of the vat. This film or ribbon was pulled up continuously held by tractors on both edges while it cooled. After 12 meters or so it was cut off the vertical ribbon and tipped down to be further cut. This glass is clear but has thickness variations due to small temperature changes just out of the vat as it was hardening. These variations cause lines of slight distortions. You may still see this glass in older houses. Float glass replaced this process.

Watch out for more gyan on many more types of glass in my next post!

Of glass & more

What is glass? And more importantly, why am I fascinated by it enough to create a whole blog on this seemingly uninteresting subject?

By definition, glass is an amorphous solid that has been around in various forms for thousands of years and has been manufactured for human use since 12,000 BC. Glass is clear, transparent and brittle. Glass is one the most versatile substances on earth, is used in many applications and in a wide variety of forms - from plain clear glass to laminated, tempered and tinted varieties.

Glass occurs naturally when rocks high in silicates melt at high temperatures and cool before they can form a crystalline structure. Obsidian or volcanic glass is a well known example of naturally occurring glass, although it can also be formed by a lightning strike on a beach, which contains silicate-rich sand. Early forms of glass were probably rife with impurities and subject to cracking and other instabilities, but examples of glass beads, jars, and eating materials first appeared in ancient Egyptian culture.

When manufactured by humans, glass is a mixture of silica, soda, and lime. Other materials are sometimes added to the mixture to “frost” or cloud the glass or to add color. The elements of glass are heated to 1800° Fahrenheit (982° Celsius). The resulting fused liquid can be poured into moulds or blown into various shapes, and when cooled, glass is a strong, minimally conducting substance that will not interact with materials stored inside. This, of course, is the glass manufacturing process in a nutshell. The actual process is quite complex.

Glass is a strange substance, defying easy scientific categorization. It is not a solid, not a gas, and not quite a liquid either. Generally, it is classified as a rigid liquid, maintaining liquid properties while acting like a solid. Heat can return the glass to a liquid and workable form, making it easy to reuse and recycle.

Glass is a favoured material for a lot of reasons. It resists chemical interactions, is easy to recycle, does not leach chemicals like plastics do, and can withstand extremes of heat and cold, although not at the same time.

So that’s the technical gyan on glass, the single object that has never failed to fascinate humans. Its applications are widespread – From crockery to mirrors to furniture to architecture, glass continues to be one of the most important substances in our everyday lives, often taken for granted.