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

1. Glass Industry in West Virginia
Making Glass
An Interdisciplinary Project of Cabell County
Schools and Marshall University’s June Harless
Center
Session 3 – 18 April 2013

2. 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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3. 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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4. Crystalline Solid Amorphous Solid
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5. 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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6. 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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10. 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
glass
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11. Glass Furnace
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12. Plate Glass Manufacturing
• Broad sheet glass production
• Cylinder glass production
• Blown glass production
• Crown plate glass
• Rolled glass
• Float Glass
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13. 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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16. 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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17. Crown Glass
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18. 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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19. 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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22. Types of Glass
• Soda-Lime
• Lead Crystal
• Flint Glass
• Borosilicate
• Safety Glass
• Laminated Glass
• Ballistic Glass
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23. 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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24. Soda-Lime Glass
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25. 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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26. Lead Crystal
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27. 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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28. Flint Glass
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29. 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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30. Borosilicate Glass
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31. 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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32. Tempered Glass
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33. Laminated Glass
• Laminated glass couples toughened glass with
a layer of plastic to contain the broken
crumbles of glass
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34. 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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35. Ballistic Glass
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36. Supporters