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May 07, 2018

History of Glass

How to turn Sand into Glass

The raw material from which glass is made is silica, the most abundant of all the earth's minerals. Milky white in color, it is found in many forms of rock, including granite. And as every beach in the world has been formed by water pounding rocks into tiny particles, sand is the major source of silica.

When you examine a handful of sand, any grain that is semitransparent - rather than black, red, yellow or some other definite color - is a grain of silica. Sand also contains other minerals, but silica is the main component because it is hard, insoluble and does not decompose, so it outlasts the others.

 


Pure silica has such a high melting point that no ordinary fire would convert it into glass. Today, lime and soda are combined with silica to produce soda-lime glass, used for making bottles, window panes, flat glass products, and cheap drinking glasses. When glass cools, its structure does not return to the crystalline structure of silica, which is opaque. Instead, it forms a disordered structure rather like a frozen liquid, which is transparent.

Making window panes, the old way

The technique for making thin, flat window glass was perfected in Normandy, France, in the 14th century. Known as crown glass, each piece was blown by a craftsman. An accomplished glass-blower could make only about a dozen windows in a day, making medieval window glass an expensive luxury.

For each pane, the molten glass is blown into a large bubble using a blowpipe. The bubble is then flattened and attached to the end of an iron rod, called a "punty" which is rotated as fast as possible by the craftsman.

The flattened bubble of glass fans out to form a circle 1m to 2m wide, depending on the size of the original bubble and the skill and strength of the craftsman.

The round, flat glass sheets were then cut for use as small window panes, particularly in churches. The "bullseye" at the center of the disc was the least transparent section, but because glass was so expensive, it would have been used anyway.

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Our latest innovations

July 27, 2018

Feasibility Studies


Stewart Engineers can help you quantify risks and ensure financial feasibility before investing in glass manufacturing. Investing in float glass is challenging for new entrants. How can you verify the viability of an idea when there are many smal... Read More→

July 27, 2018

Glass Manufacturing


Stewart Engineers builds high-quality float glass manufacturing facilities around the world. We use our considerable experience in float glass to design and build float facilities that maximize profit. Technologies like the StewartFloat® ... Read More→

June 19, 2018

Make CVD Part of your Future


Glass manufacturers began to use CVD for online coatings in the 1960’s. Pilkington was the first to develop a marketable product, Reflectafloat. Over the lifetime of the product, it was made in both the tin bath and the lehr. Reflectafloat... Read More→

May 07, 2018

History of Glass


How to turn Sand into Glass The raw material from which glass is made is silica, the most abundant of all the earth's minerals. Milky white in color, it is found in many forms of rock, including granite. And as every beach in the world has been for... Read More→

May 07, 2018

Float Glass Cutting and Packing


The final online manufacturing process for float glass is the Cutting and Packing line. The cutting and packing conveyor is immediately downstream of the annealing lehr. It is comprised of special roller sections that are capable of transporting gla... Read More→

May 07, 2018

Float Glass Annealing Lehr


What is a lehr? A glass annealing lehr oven- often just referred to as a 'lehr', is a long, temperature controlled, kiln. Lehrs are typically 6m wide and 120m long, with an adjustable temperature gradient through which the glass passes. In t... Read More→

May 07, 2018

Glass Forming


Forming Technology Flat glass is manufactured using one of three processes: the sheet process, the plate process, or the float process. The float glass process has, almost entirely, replaced the sheet glass and plate glass processes. Sheet Glass Th... Read More→

May 07, 2018

Glass Materials and Batching


Glass contains three major categories of constituents - formers, fluxes, and network modifiers. Silicon dioxide (SiO2), or sand, is used as the former and basic constituent with soda ash (Na2CO3) as the flux. Lime (CaCO3) and dolomite (CaCO3MgCO3) a... Read More→

May 07, 2018

Glass Melting Process


Melting The typical melting furnace is a Six Port Cross Fired Regenerative furnace with a capacity of 500 tons per day. Cross fired regenerative furnaces have been built for very small and very large melting areas. The smallest units may be unecono... Read More→

April 10, 2018

Glass Coating Technology Comparison


A variety of techniques are available to deposit thin films onto flat glass. The most widely used of these for producing high-quality functional coatings can be subdivided into two classes: Physical Vapor Deposition (PVD) and Chemical Vapor Depositi... Read More→