4 An Introduction to Glass Glafo. Bulk batch 44 Pellets 45 Charging 46. Transport and storage 48. How is glass formed? 11

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1 Table of contents FOReWORD 3 1. What is glass? 10 introduction 10 How is glass formed? 11 substances that can form glass 13 The structure of glass 14 Glass forming oxides 14 Network breaking oxides 14 Network modifying oxides 15 Additives 15 properties of glass 16 Viscosity 16 Crystallisation 17 Surface tension 19 Thermal properties 20 Density 22 Optical properties 23 Mechanical properties 25 Electrical properties 27 Chemical resistance 27 Weathering 29 REFERENces and further reading Raw materials 32 introduction 32 Moisture content 35 Grain size 35 Weighing 36 MAIN constituents 36 Sand 37 Soda ash 38 Potash 39 Lime 39 Lead oxide 40 Barium carbonate 40 Zinc oxide 40 additives 41 Melting accelerators 41 Refining agents 42 Aluminium-based raw materials 42 Opacifiers 43 Colouring agents 43 batch 44 Bulk batch 44 Pellets 45 Charging 46 cullet 47 Transport and storage 48 batch formulae and glass recipes 48 Vitreous oxide factor of a raw material 48 REFERENCES AND FURTHER READING The melting and annealing 52 THE MELTING PROCESS 52 Primary melting 53 Refining 55 Homogenization 58 Melting until seed free 59 Conditioning 60 ENERGY CONSUMPTION 61 Batch and pellets 61 Residual glass 61 Cullet 61 THE ANNEALING PROCESS 62 Annealing stresses 62 Compatibility stresses 64 Some aspects of annealing glass 64 Practice concerning annealing glass 65 Calculating the annealing process 66 EXAMINING FOR STRESSES 67 Annealing stresses 67 Compatibility stresses 68 DEALING WITH STRESSES 68 Annealing stresses 69 Compatibility stresses 69 REFERENCES AND FURTHER READING Furnaces and refractories 72 HISTORIC FURNACES 72 CONTEMPORARY FURNACES 72 POT FURNACES 72 Electric furnaces 73 Multi-pot furnaces 74 DAY TANKS 74 CONTINUOUS TANKS 74 HEAT-TREATMENT FURNACES 75 Reheating furnaces 75 Annealing furnaces or lehrs 75 4 An Introduction to Glass Glafo

2 Tempering ovens for pots 76 Fusing kilns 76 HEAT EXCHANGER 77 Recuperative heat exchangers 77 Regenerative heat exchangers 77 BURNERS 78 Oil burners 78 Gas burners 78 Oxy-fuel burners 78 REFRACTORIES 78 Areas of usage 79 Important data for purchase and use 80 REFRACTORIES IN FURNACES 80 POTS 82 Which quality of pot should one choose? 82 Clay pots 82 Sillimanite pots 83 Zirconia mullite pots 83 Handling pots and rings 83 Corrosion of pots 85 RINGS 85 REFRACTORIES FOR TANK FURNACES 86 RECYCLING REFRACTORIES 87 REFERENCES AND FURTHER READING Process Control 90 INTRODUCTION 90 PROCESS CONTROL IN MANUFACTURING 91 Tips for measuring temperature in pot furnaces 91 Special requirements of tank furnaces 92 Acid polishing 93 MEASURING TEMPERATURE 93 Thermocouple 93 Optical pyrometers (radiation pyrometer) 96 MEASURING LEVELS, PRESSURE AND FLOW 97 Measuring levels 97 Measuring pressure 97 Measuring flow 97 MONITORING AND REGULATING 98 Temperature regulation 98 Ratio regulation 99 Proportional, integral and derivative feedback 100 Displaying, following and registering 100 REFERENCES AND FURTHER READING How do you colour glass? 104 INtroduction 104 Light and colour 106 How the eye perceives light 106 Absorption of light produces colour 107 DESCRIBING COLOUR 107 measuring colour 107 Dominant wavelength, saturation The L*a*b system 108 common ways of colouring glass 108 Ion colours 109 Striking colours 109 Opal glass 109 green glass 110 Iron oxide (blue-green, green, yellow-green) 110 Chromium oxide (green to greenish yellow) 110 Blue glass 111 Cobalt oxide (cobalt blue) 111 Copper oxide (blue-green, turquoise) 111 Violet glass 111 Manganese oxide (violet) 112 Neodymium oxide (violet purple) 112 Nickel oxide 112 YELLOW glass 112 Cadmium sulphide (yellow, orange, red) 113 Titanium dioxide (pale yellow) 113 Sulphur (yellow, yellowish-brown, amber Red glass 113 Gold ruby (red) 113 Copper ruby (red, reddish-brown) 114 Selenium (yellowish orange, ruby red, pale white glass 115 Fluorine opals 115 Phosphate opals 115 other ways of colouring glass 116 Rods, crushed cullet and glass powder (frit) 116 Glass painting and screen printing enamels 116 Shimmering glass 117 Colouring in the feeder 117 WHAT CAUSES DISCOLOURATION? 118 Raw materials of glass 118 Refractories 119 Cullet 119 Solarisation 119 decolourising 120 An Introduction to Glass Glafo 5

3 Chemical decolourising 120 Physical decolourising 120 Common decolourising combinations 120 REFERENcEs and further reading Types of glass 124 introduction 124 quartz glass 125 water glass 125 Soda glass 125 Container glass 126 Domestic wares 126 Flat glass 126 Borosilicate glass 128 crystal glass 128 Lead crystal 129 Crystallin 129 Fibreglass 130 Mineral wool 130 Continuous glass fibre 131 Optical fibres 131 Special glasses 132 Glass-ceramics 132 Aluminosilicate glass 133 Opal glass 133 Optical glass 133 Screen glass 134 Solder glass 135 Foam glass 135 Bioactive glass 135 Glass concrete 135 REFERENces and further reading GlassmakinG 138 GLASS CRAFT IN THE HOT SHOP 138 Making a wine glass 139 Flared bowl 140 TOOLS 140 The blowing iron 140 Gathering iron, gathering ball and ladle 141 Punty 141 Shears and other tools 142 MOULDS 142 Rotating moulds 142 Fixed moulds 143 Centrifuging, casting and pressing 144 CRAFT TECHNIQUES 144 Gathering and pre-blowing 144 Blowing 144 Cracking off 145 Pressing 146 Centrifuging 147 Casting 147 Stamp casting 148 Flame polishing 148 DECORATING GLASS IN THE HOT SHOP 149 Overlay and underlay multilayered glass 149 The Graal technique 150 Ariel 150 Crushed cullet and powder of coloured glass 150 Filigree and threaded glassware 150 Millefiori glass 151 Incalmo 151 Bubble glass 152 Crackled glass (craquelle) 152 Fusing and slumping 152 Pâte de verre 153 Lampwork / flamework 153 Inserting objects in molten glass 154 SHEET GLASS 154 CONTAINER GLASS 155 Raw materials 156 Melting 156 IS machines 157 Lightweight containers 158 Machine-made domestic hollow-ware 158 FIBREGLASS 158 Fibreglass for insulation 158 Continuous glass fibre 161 REFERENCES AND FURTHER READING Finishing and decoration 166 CRACKING OFF 166 Edge melting 167 SAWING 167 CUTTING 167 Cutting of decanter stoppers 168 Puntying 168 Machine grinding 168 DRILLING An Introduction to Glass Glafo

4 POLISHING 169 Bristle polishing 169 Flame polishing 169 Acid polishing 169 ENGRAVING 170 Laser engraving 170 SANDBLASTING 170 ETCHING 171 Matt embossing with a stamp or stencils 171 STAINING 171 PAINTING 171 Enamels 172 Krinkle ice 172 Lustre paint 172 Organic paints 172 Precious metals 173 PRINTING 173 Transfers 173 Screen printing 173 LEAD MOUNTING 174 TIFFANY TECHNIQUE 175 SURFACE COATING 175 Low-emission glass 175 Self-cleaning glass 175 Mirror glass 176 Electrically conducting glass 176 TEMPERING 176 Thermal tempering 176 Chemical tempering 177 LAMINATING 177 FIRE-RESISTANT GLASS 179 CUTTING 179 Water cutting 179 Laser cutting 179 GLUING 179 BENDING 180 INSPECTION AND SORTING 180 SIGNING 180 PACKAGING 180 REFERENCES AND FURTHER READING Quality and Defects 184 QUALITY SYSTEMS 185 What is a quality system? 185 Marking and standards 186 FOLLOW-UP AND PROCESS CONTROL 188 Operational control 188 Material checking 189 Inspection 189 Instruction and training 190 What do you do when you detect a fault? 190 Measures 191 DEFECTS AND WHEN THEY CAN OCCUR 191 Raw materials and batch 191 The melting process 194 Refractory materials 195 Manufacture 197 Reheating and flame polishing 199 Cooling 199 Acid polishing 200 Storage and handling 200 REFERENCES AND FURTHER READING The environment 204 INTRODUCTION 204 WORK ENVIRONMENT AND PROTECTION 205 The work environment in the hot shop 206 Mechanical work environment 206 Primary measure 210 Secondary measures 210 INJURIOUS RAW MATERIALS 210 Hazardous substances 214 ENVIRONMENTAL IMPACT 214 RECYCLING 217 Waste products 218 REFERENCES AND FURTHER READING A history of Swedish glass 222 GLASS BEFORE From luxury item to everyday product 223 More glassworks and improved technology 226 The glassmaking community 228 Personnel 228 Working conditions and wages 229 Housing 230 The popular movements 231 BOTTLES, LAMPS AND WINDOW GLASS 232 GLASS IN THE 20TH CENTURY 233 An Introduction to Glass Glafo 7

5 Artists to industry 234 Exclusive art glass 235 More beautiful everyday wares 235 International breakthrough 236 A new approach at several glassworks 236 Oh land of design! 237 A breath of fresh air 238 Studio glass makes its entry 239 Diversity of Swedish glass 240 GLASS AT THE TURN OF THE MILLENIUM 241 REFERENCES AND FURTHER READING 243 Cover pictures: Photo: Tommy Durath Chapter vignette pictures: 1. Vase, design Olle Brozen, Orrefors Kosta Boda AB. Photo: Elisabeth Flygt, Glafo, the Swedish Glass Research Institute 2. Addition of pellets and cullet. Photo: Lars Gunnar Johansson, Glafo, the Swedish Glass Research Institute 3. Cooling of colour sample. Photo: Tommy Durath 4. Gathering of glass. Photo: Elisabeth Flygt, Glafo, the Swedish Glass Research Institute 5. Incorrect furnace pressure with flames escaping from the kiln opening. Photo: Hans Fredriksson, Glafo, the Swedish Glass Research Institute 6. Store of coloured rods. Photo: Elisabeth Flygt, Glafo, the Swedish Glass Research Institute 7. Exhibition of various types of glass at Glafo, the Swedish Glass Research Institute. Photo: Elisabeth Flygt, Glafo, the Swedish Glass Research Institute 8. Half parison. Photo: Lars Gunnar Johansson, Glafo, the Swedish Glass Research Institute 9. Sculpture, Målerås glassworks. Photo: Elisabeth Flygt, Glafo, the Swedish Glass Research Institute 10. Vase, Rosebud, design Erika Lagerbielke, Orrefors Kosta Boda AB. Photo: Pål Allan 11. Sculpture, Transjö hytta. Photo: Elisabeth Flygt, Glafo, the Swedish Glass Research Institute 12. Ida packaging glass, 1937, Pukeberg. Archive of Smålands museum Sweden s Museum of Glass, Växjö. 8 An Introduction to Glass Glafo