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Making Glass Ingredients Silica Soda Ash Lime Metal Oxides Glass Making Processes General Process Plate Glass Production Types of Glass Soda-Lime Lead Crystal Flint Glass Borosilicate Safety Glass Laminated Glass Ballistic Glass
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Glass Industry in West Virginia
Making GlassAn Interdisciplinary Project of Cabell County
Schools and Marshall University’s June Harless Center
Session 3 – 18 April 2013
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Outline• Making Glass
– Ingredients• Silica• Soda Ash• Lime• Metal Oxides
– Glass Making Processes• General Process• Plate Glass Production
– Types of Glass• Soda-Lime• Lead Crystal• Flint Glass• Borosilicate• Safety Glass• Laminated Glass• Ballistic Glass
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Glass
• Contrary to common misconceptions, glass is NOT a liquid
• It does not slump in old windows• Because of the molecular arrangement during
cooling, glass does not form distinct crystals and is classified as an amorphous solid
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Crystalline Solid Amorphous Solid
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Ingredients
• Glass is produced with simple ingredients:– Silica (often about 70%) from sand– Lime– Sodium oxide from lime by the Solvay process– Cullet (recycled glass)– Metal oxides
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Metal Oxides• Calcium oxide (quicklime), magnesium oxide and
aluminum oxide strengthen the glass• Lead oxide, barium oxide, thorium oxide and
lanthanum oxide increase the refractivity of the glass producing a more brilliant glass
• Sodium sulfate, sodium chloride or antimony oxide is added to reduce the air bubbles in the glass
• Iron may be added to glass to increase heat absorption
• Boron oxide may be added to glass to provide protection from cracking during changes in temperature
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Glass Making Process
• Glass making requires several furnaces• A small furnace preheats the ingredients for
glassmaking• An ancillary furnace warms the ceramic forms
for the glass• The hottest furnace melts and mixes the
materials• A small furnace anneals and cools the formed
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Glass Furnace
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Plate Glass Manufacturing
• Broad sheet glass production• Cylinder glass production• Blown glass production• Crown plate glass• Rolled glass• Float Glass
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Blown Plate Glass
• Broad sheet glass production – a cylinder of glass was blown then cut into a sheet that was cooled on an iron plate
• Cylinder glass production – similar to broad sheet glass except that a larger cylinder was blown into an iron mold that was cut and cooled on an iron plate. This process was used by William Blenko to make stained glass
• Blown glass production – starts with broad or cylinder glass but is polished on one or both sides
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Crown Glass
• Crown plate glass - glass was blown into a hollow iron globe that was flattened by spinning to make a disc
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Crown Glass
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Because crown glass does not have uniform thickness, people assume that the glass has slumped over time.Early glaziers naturally put the thicker side of the glass in the lower mullion.
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Float Glass
• Melting point of glass 1500o F• Melting point of tin 450o F• Molten glass at 1500o F is poured onto a
shallow pan of hot molten tin. The glass harden as it cools and is passed to an annealing oven where the glass sheet gradually cools and is cut to desired sizes
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Types of Glass
• Soda-Lime• Lead Crystal• Flint Glass• Borosilicate• Safety Glass• Laminated Glass• Ballistic Glass
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Soda-Lime Glass
• Typical glass from which most tableware, art glass and plate glass is manufactured
• 75% silica with Na2CO3, Na2O, CaO, MgO and Al2O3
• Over 90% of all glass is soda-lime
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Soda-Lime Glass
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Lead Crystal
• Lead crystal has a composition similar to soda-lime glass except PbO (at least 24%) replaces the CaO giving the glass a high reflectivity and index of refraction. Waterford and Steuben are well known makers of lead crystal
• Modern “lead crystal” has BaO, ZnO or K2O rather than PbO since lead is a biological hazard
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Lead Crystal
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Flint Glass
• Formerly had up to 60% PbO to increase the index of refraction for scientific lenses.
• Modern flint glass lenses have TiO2 or ZrO2
• Called “flint glass” for the flint stones found among the silica deposits in England were glass was produced in the 1600s
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Flint Glass
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Borosilicate Glass
• has high levels of B2O3 to soda-lime glass mixture that raises melting point, increases ability to withstand thermal shock and strengthens the glass.
• Pyrex, Kimex and others scientific and kitchen glassware are borosilicate glass
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Borosilicate Glass
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Safety glass
• Tempered or toughened glass is produced by controlled heating creating internal stress that causes the glass to break into small crumbles rather than jagged shards when broken
• Tempered glass is required in doors and many windows
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Tempered Glass
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Laminated Glass
• Laminated glass couples toughened glass with a layer of plastic to contain the broken crumbles of glass
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Ballistic Glass
• “Bulletproof” glass is made from a combination of hard and soft glass layers. All layers must have the same index of refraction.
• Recent innovations allow a transparent plastic layer to be adhered to the inside of traditional glass to provide resistance to penetration from a projectile
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Ballistic Glass
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