Glassblowing: an ancient art still practiced today
Glassblowing is nearly as old as human civilisation, but it still holds an almost otherworldly appeal. Watching a skilled glassblower coax a recognisable form out of a lump of molten glass called a “gob” is a magical, alchemical experience.
What’s interesting is that the glass bottle that holds your beer, wine, jam or honey is produced using exactly the same process (only at a much, much larger scale). When an artisan glassblower approaches a new piece, first they need to melt the raw materials – sand (silica), soda ash and limestone – in a crucible to form the glass, at a temperature of about 1 300 °C. Then they use a blowpipe to gather up the molten glass in a gob on the tip (just as you would honey using a honey-dipper). Then they roll the gob on a flat sheet of steel or marble called a marver, to cool the exterior of the gob and begin to shape it.
Air is then blown into the pipe, forming a bubble, while the blowpipe is constantly rotated to ensure an even shape. During this process the gob is regularly inserted into a secondary furnace, known as a glory hole, to ensure that the correct temperature is maintained. Finally, the resultant shape is cut off the blowpipe using shears, and the finished piece is annealed, or cooled in a controlled manner to ensure its durability.
In industrial glass container manufacture, just as in artisanal glassblowing, raw materials are combined according to precise ratios and melted in a furnace at around 1 500 °C. Individually sized gobs of molten glass are guided into moulds, and the opening of the bottle is formed. Compressed air is then used to inflate the glass into its final form, exactly as a glassblower would.
There are two distinct methods used to create glass containers on an industrial scale, as can be seen in the video alongside.
The first, known as the blow-blow method, is used for larger containers. In this process, compressed air is blown into the molten gob to create a cavity, resulting in a hollow and partly formed container. This is then transferred to the second moulding stage, where compressed air is used again to form the final shape. The second is known as the press-blow method. This time a metal plunger is used to press a cavity into the gob in the blank mould before compressed air is used to form the final container. Variations in this method allow for either narrow or wide-necked containers to be formed.
Once the shapes have been formed, they are likewise annealed, and then go through several additional processes to strengthen and coat them for transport. They’re tested for quality and branded according to the customer’s requirements. Glassmakers – whether working at an individual or industrial scale – experience the same wonder and beauty. Their methods haven’t changed substantially over thousands of years, but the magic of creation – from raw materials, through the furnace, to the finished product – never grows old.
Women in Consol:
Teslyn Daniels – Group Batch & Melting Operations Manager
Melting is a fundamental, technically specialised component of the glassmaking process. The Group Batch & Melting Operations Manager is a crucial, key position within an operation such as Consol’s. They advise on and manage operational challenges at all seven operating plants; devise and implement chemistry-related programmes and develop batch recipes to achieve desired glass conditions and colours; reduce costs; train new melting specialists; and improve emissions and other sustainability measures. Consol's Teslyn Daniels became the first woman in the company appointed as Group Batch & Melting Operations Manager in January 2020. Teslyn joined Consol in 2006 as a laboratory technician, and rose steadily through the ranks to become one of the most important technical specialists in the organisation, with overall responsibility for the 14 furnaces across Consol’s seven sites in Africa.
Reflecting on what she has accomplished, Teslyn says: “I feel truly honoured and I hope that it motivates many other women in the business to strive to reach their full potential. Getting to this point involved sacrifices and hard work, but overall the successes far overshadow these. At Consol, I believe that women bring new leadership styles and many other benefits to the company. Over the past 10 years we have not just seen women excel in our business, but I am happy to see that women of colour have also advanced. This shows that if we remain committed to a future in which impartial recruitment and promotion is practised then we will see more women move forward.”