Making GlassBRIEF HISTORY OF GLASSPre-historic man is known to have used natural glass for arrowheads and simple tools. This glass was created by sudden volcanic eruptions followed by rapid cooling. At about 4000 BC the first man-made glass was produced in the Near East. This was in the form of glazes used for coating beads. Hollow glass vessels date to about 1500 BC and were made by covering a sand core with a layer of molten glass. When the glass solidified the sand was scooped out, leaving small vessels. Often these vessels were decorated by applying threads of coloured glass to the surface and arranging them in attractive patterns. It was not until the 1st century B.C. that glass vessels, as we know them today, made their appearance. It was then that the glass makers realised that glass could be blown into various shapes. The introduction of the blowing iron was probably the most important step in the development of glass manufacture. Due to impure materials used in the early days most glasses were highly coloured, when required, by the addition of colouring materials. This, of course, brings to the days of the Roman Empire and it was at this time that glass was first made in Britain. Needless to say, the science of glass technology did not exist and glass making depended entirely on the skills and closely guarded secrets of individual glass makers. As the Roman Empire disintegrated, glass making spread throughout Europe and the Islamic countries of the Near East. Better raw materials were used and more efficient melting furnaces were built. Sand, which is the main constituent of glass, was in plentiful supply. For flux, ash from local forest plants and trees were used. This contained a high proportion of potash and thus potassium oxide, rather than sodium oxide, was an important consistent. Wood was used for fuel and consequently glassworks were normally situated in forest areas away from towns. Until the 16th century the main product of Northern European glass-makers was window glass of various kinds. There were two methods of producing flat glass and both involved blowing a bubble of glass. In the "crown" method the glass-maker blew a large bubble of glass, which he then spun rapidly, while the glass was still soft. Centrifugal forces took care of the rest and he finished up with a sizeable disc of glass attached to his blow pipe in the centre. The blow pipe was then removed and the disc was annealed. This disc was then cut into panes of different sizes. Obviously the size of the panes was rather limited and hence the small windows in ancient houses. Where the blow pipe was attached there was an attractive "bull’s-eye" left behind. Panes of glass with a bull’s-eye are still in demand for decorative uses. In the cylinder, or broad glass method, the glass maker blew a bubble, which he then elongated by swinging it in a pit into a cylinder of glass closed at both ends. The ends were then cut off, the cylinder was cut lengthways, it was re-heated and was then opened out into a flay sheet. It is interesting to note that this method was in use up to the 1930’s in Europe and may even be used today in some underdeveloped countries with a limited demand for window glass. After the fall of the Roman Empire glass making traditions appear to have continued around the Mediterranean and the Near East. Venetian glass makers gained a reputation for technical skill and artistic ability, which is still in evidence today. By the 15th century, Venice developed a thriving glass export business but its monopoly did not last forever. In spite of all precautions not to divulge the Venetian secrets, some glass- makers succeeded in escaping and set up glassworks throughout Europe. In Britain, as early as in 680 AD, there was a glass industry around Jarrow and Wearmouth. From the 13th century AD there is evidence of a glass industry in the Weald and the afforested area of Surrey and Sussex around Chiddingfold. Window glass was again the main product and glass from Chiddingfold was used to glaze the old chapels of St. Stephen and St. George at Windsor. In 1575, a patent was granted to an Italian Jacopo Verzelini to make "drynkyne glasses such as be accustomable in the town of Murano" and to teach British workers how to make them. As mentioned before, wood was the fuel used and as forests were becoming depleted, wood was becoming scarce. Wood was in demand not only by the glass industry but other industries, notably shipbuilding, were competing for it. This hastened the change to coal-fired furnaces and in 1615 there was a Royal Proclamation forbidding the use of wood for glassmaking. The need for coal and other new materials decided the location of the present glass industry in the areas where these were available. Thus, North West England and Yorkshire were the obvious choice. In these areas there was ample supply of coal, large glassmaking sand deposits, limestone in nearby Derbyshire and soda ash from the extensive salt deposits in Cheshire. The next milestone in the history of glass was the invention of lead crystal glass. The establishment of the Royal Society of London in 1660, which had as it’s objective the promotion of science, played an important part in the history of glass. Several members of the Worshipful Company of Glass Sellers of London, incorporated in 1664, were also members of the Royal Society. The Company supported George Ravenscroft in his scientific research into a "particular" sort of Christaline Glass resembling Rock Christall". Ravenscroft, attempting to counter the effect of crizzling and clouding caused by the fumes from an excess of alkali from batch, added lead to the raw materials and produced a new material which was far superior than the glass used so far in the Venetian composition. The new glass was softer and thus easy to decorate by cutting and grinding, it had a longer working range, enabling the glass-maker to produce more intricate designs and above all it had a higher refractive index giving it more brilliance and beauty. The higher refractive index was invaluable to the optical industry. Thanks to Ravenscroft’s invention optical lenses, astronomical telescopes, microscopes, etc., became possible. The demand for high quality flat glass for large windows, mirrors and coach doors could no longer be satisfied by the existing methods of flat glass manufacture and by the mid-seventeenth century, glass casting was developed. The glass was poured from crucibles into pan-shaped moulds. The surfaces of this glass were uneven and were ground and polished by hand. High quality cast plate glass production was not introduced in Britain until 1773 when the British Cast Plate Glasses Company was formed in Ravenhead, St. Helens, Lancashire.Another English invention was the glass cone. The cone was the glasshouse but was shaped in such a way that it acted as a chimney to remove unpleasant gases and make working conditions considerably more bearable. A few cones dating from the 17th century have been preserved notably one at Stourbridge at Stuart Crystal Company, one at the Alloa glass works of United Glass Ltd, and one at Catclifffe near Sheffield. The British glass industry was for many years hampered by heavy taxation. Excise duties on the amount of glass melted in a glasshouse were levied continuously from 1745 to 1845. Excise officers were on duty in every glasshouse, checking all operations. All glass had to be accounted for. In order the avoid this duty, glassworks were set up in Ireland to take advantage of the Free Trade Acct of 1780. However, this respite was short lived as in 1825 Excise Acts were enforced in Ireland and glass production there came to an end. Eventually, as a result of a recommendation of the Inquiry of the Excise Commissioner in 1835, the Excise Acts were repealed in 1845. It was only then that the industry could start to develop. Joseph Paxton’s Crystal Palace for the Great Exhibition of 1851 marks the beginning of the discovery of glass as a new material. This revolutionary new building encouraged the use of glass in public, domestic and horticultural architecture. Glass manufacturing techniques were also improving. The higher temperatures needed for melting better quality glass were made possible by the introduction of the main producer of optical and other special glasses. With the outbreak of the First World War, Britain suddenly became cut off from glass supplies badly needed for the war effort. Until then glassmaking was a craft, almost divorced from scientific footing. Thus in 1915 the Department of Glass Technology was created at Sheffield University. The Department devoted itself to research on glass and then to the training of glass technologists. Dr. Turner became the first Professor of Glass Technology, a chair he held until his retirement in 1944. The following developments are worth noting:1904 First commercial production of fused silica The development in the mass production of glass containers started when Ashley, having realised that the hand making and mouth-blowing of bottles could not be mechanised without altering the principles involved, introduced the semi-automatic Ashley machine. Hand gathering and feeding of glass to the machine was the main obstacle to fast production speed. 1901 Homer Brooke produced the first successful automatic
feeder device The IS machine is still predominant in the glass container industry and speeds well above 12,000 bottles per hour can be achieved. Flat glass production underwent equally revolutionary changes and thus in:1870 Rolled glass produced by Chance Brothers Glass in Vacuum science had the following landmarks:1879 First electric light bulb |