Glass In all its Glory: Part 2

Martin Pitt looks at the Industrial Age, which saw the mechanisation of glass manufacture, but also featured major chemical engineering developments

THE MOST important chemical engineering contribution to glass manufacture undoubtedly came from Belgian chemist Ernest Solvay (1838–1922), a member of an industrial family which owned a salt works.

In 1859 he got a job as a manager on his uncle’s gas works and was tasked with finding a use for the ammoniacal liquor which was largely a waste product. Experimentally, he discovered the process which bears his name, being unaware that it had been known since 1811 but chemists had been unable to convert it to an industrial process.

In 1861 with his brother Alfred (1840–1894), a practical engineer and entrepreneur, they patented the process and in 1863 formed a company, Solvay SA, which still exists today. It was the chemical engineering, rather than the reaction, which was patentable. In particular, the column in which CO2 reacts with ammonia, giving continuous manufacture of sodium carbonate from salt and limestone via ammonium carbonate, in which nearly all the ammonia was recycled.

In 1865 they started limited production. Seven years later German-born British industrial chemist Ludwig Mond (1839–1939) visited. It so impressed him that in 1873 he went into partnership with John Brunner (1842–1919), the general manager of an alkali works, to bring the Solvay process to commercial operation, forming Brunner, Mond & Co with a largely borrowed capital of £20,000 (about £1.9m (US$2.5m) today). In 1878 they were selling at below the price of Leblanc process manufacturers and became the wealthiest British company of the time. The Solvay brothers quickly found partners in other European countries using the improved process, while Brunner Mond had the UK and US market. It rapidly overtook the Leblanc process and glass companies were often combined with soda ash plants.

The second important contribution is energy saving. In 1856, two German inventors, Carl Wilhelm Siemens (1823–1883) and his brother Friedrich (1826–1904), came to Britain with their invention, overcoming several false starts to establish the world’s first regenerative furnace in a Rotherham glassworks four years later. The furnace had two chambers with blocks of ceramics which absorbed the heat of the exit combustion gas or heated up the inlet air and gas, by the flow being periodically reversed. Instead of glass being melted in pots, it was in a rectangular tank from which glass could be withdrawn for the manufacturing process such as automated bottle production. Factories commonly had two tanks, one in use, one heating up. They were rebuilt each year. Carl Wilhelm, who eventually became Sir Charles William Siemens, had also invented an electric pyrometer which helped control the process. Friedrich went home and developed a large glass company. These two developments were the beginning of modern mass manufacture.

Prolific British inventor Sir Henry Bessemer (1813–1898) also contributed to the understanding and technology. He actually set up a small glassworks at the rear of his house. The existing method of mixing the components was by shovelling from different piles. By grinding and mixing the solids to a more intimate mixture, the time to get a glass melt could be reduced by two-thirds, and it was more homogeneous. Mechanical mixing of batches of solids to go in the tank is normal today.

Mineral processing

Substantial processing of the constituents occurs before glass is made. In particular, separating out unwanted materials, preliminary chemical treatment depending on the contaminants, and achieving the right particle size range. Glassy minerals other than silica are also used, notably aluminosilicates such as feldspar which contains aluminium, sodium, and potassium as well as silicon and oxygen.

Bottles and jars

In the 19th century, sealed bottles and jars increased storage time and reduced costs. The metal screw-top jar with rubber seal (1858) was reusable for both commercial and home storage of cooked or pickled fruit or vegetables. The crown cap (1892) held carbonated drinks. A refundable deposit was charged if taken away from a drinking establishment. Bottle-makers had their name embossed so only took exactly the same glass for cullet, getting close to a circular economy. It was only in 1903 that machinery replaced human lungs for the first fully automatic bottle-making machine. American glassblower Michael J Owens (1859–1923) used a piston pump to suck the right amount of glass into a mould and reversed it to blow it into shape.

Milk had normally been dispensed into the customer’s jug, but in England in 1880, the first sealed glass bottles were delivered by a milkman (or milkwoman, especially in wartime). A variety of closures were used until the advent of the foil cap after the Second World War when aluminium became more available (see TCE 990). A hazard was birds pecking through to drink the milk while the bottle was on the doorstep. Householders placed the washed empties out to be collected by the “milkie”, and they were sterilised and reused on average 30 times. The profession was largely put out of business when supermarkets started selling milk in double-size plastic bottles at less than cost price in order to get customers in. However, there has been a small resurgence of doorstep deliveries in glass.

Windows

In 1834 British glassmaker Robert Lucas Chance (1782–1865) introduced an improved version of the broad sheet process, with his workers blowing into wooden moulds up to 2.4 m long, and mechanically cutting and polishing on leather. The prestige building, the Crystal Palace (1851), had nearly 300,000 panes of 124 x 25 cm made by this process. The lower cost and larger sizes meant that it rapidly replaced crown glass.

The age of steam allowed the greater production of plate glass. Molten glass was poured onto a metal plate and powered rollers spread it into a thin, flat sheet. This rolled glass was good enough for skylights or less important windows, and could be ground and polished for better results. Windows for prestige stores in the US increased from seven by three feet (2.1 x 0.9 m) to 14 by eight feet (4.3 x 2.4 m) between 1830 and 1860.

In 20th century US a key part of plate glassmaking was little different from Roman times except in scale and quality. The sand mixture was melted in clay pots, the difference being a larger furnace at 1,600°C containing 20 pots holding more than a tonne each. Each pot took up to three years to make, from weathering clay, mixing, hand-making to ensure no flaws, and storing for at least six months to season. The average pot life was 20 days, so a large factory might have 5,000 in storage (pot melting is still done for smaller-scale production or multiple products). To anneal the glass, it was then passed through a tunnel 250 m long over five hours in which the temperature was gradually reduced, before grinding and polishing.

In 1860, Henry Bessemer had actually made a tank furnace at his home from which a sheet of glass 76 cm wide was extruded through rollers horizontally to a length of 20 m (folding up against the wall), before being shut off because the heat was too much in the room. He sold the method to a glass company but it was never commercialised. In 1912, Belgian inventor Émile JC Fourcault (1862–1919) opened a plant drawing a sheet of glass vertically (like a soap bubble) from a tank through rollers up a 10 m tower, which greatly reduced the cost of moderate quality window glass.

In 1918 Henry Ford (1863–1947) was dissatisfied with the cost of plate glass windows for his automobiles, so got his chief assembly-line engineer Clarence W Avery (1882–1949) to try and make a continuous process, which he achieved in 1921, despite knowing nothing of glassmaking. Glass came horizontally out of a tank in a ribbon not dissimilar to Bessemer’s invention and through the annealing process. However, the quality was very poor. By involving British glass company Pilkington Brothers, successful production started in 1922 and was followed by continuous grinding process, simultaneously for the top and bottom, in 1935.

It was at Pilkington Brothers, St Helen’s, Lancashire in 1952 where a revolutionary process was invented by engineer Alastair Pilkington (1920–1995) (no relation to the owners) in which glass was fed continuously on to a bath of molten tin at 800°C, giving a smooth surface on both sides. It took him and colleagues seven years to develop and patent it, and in the 1960s other major manufacturers bought licences. Bessemer had experimented with liquid metals, and there had been some attempts in the US in 1902, but it often takes a long time and money to go from idea to practical process and saleable product (in this case £4m).

Problems included chemical and fluid mechanical. The exact chemical content of the tin and the atmosphere above had to be controlled to prevent reaction with the glass or oxygen to maintain the clean surface. Contaminants could be carried in from the glass mixture or by reaction with the refractory components. Viscosity and surface tension affected the time required for the top surface to relax, and careful modelling with pilot plant studies was needed. It needed annealing on a further bath until it could be taken off on rollers. Changing the thickness or width was a major challenge, but it eventually took over from plate glass for most window purposes. The inventor became Sir Alastair in 1970, chairman of the company in 1973, and president on his retirement in 1985.

The modern lens

It was German inventor Otto Schott (1851–1935) who revolutionised optical glass manufacture. The son of a window glassmaker, he studied chemical technology (the forerunner of chemical engineering) at technical college and university and gained a doctorate in glass science. There was then no predictive model of the effects of glass composition. To remedy this, he made hundreds of batches of glass with different compositions using clay beakers, stirring each carefully with a clay tobacco pipe to eliminate bubbles, and measured their properties. Along with Ernst Abbe (1840–1905), the inventor of the refractometer and pioneer of optical instruments, and Carl Zeiss (1816–1888), an optical instrument maker, they set up a company still known today as Schott AG using Schott’s formulations and Abbe’s optical theory. They gained a near global monopoly on optical glass. Later Schott developed borosilicate glass, which has very low thermal expansion and can be heated directly, used for laboratory equipment up to pilot scale, thermometer tubing, covers for gas lamps, and domestic cookware.

In the First World War, Britain could no longer get the fine Zeiss binoculars to look for warships and U-boats, nor the Schott optical glass for gunsights. A relatively unknown academic expert on glass technology, William ES Turner (1881–1963), was called upon to teach British glassmakers to get the necessary quality and quantity, which he achieved in less than a year, setting up a Department of Glass Technology at the University of Sheffield. Come the Second World War, there was a need for glass vacuum tubes for radio valves so his outreach classes began again. In 1943 he married Scottish glass artist Helen Nairn Monro. Clothing was rationed, but his bride wore a wedding dress and shoes of a new secret material, glass fibre. Transparent to microwaves, it was being developed to cover radar equipment for protection and secrecy.

Glass fibres

Glass fibre was invented by Prussian-American inventor Hermann Hammesfahr (1845–1914) in 1880, and lampshades of it were displayed at the World’s Fair in Chicago in 1893. A dress made of glass fibre and silk was made for popular US actress Georgia Cayvan (1857–1906). She caused a sensation on stage and at the Fair, but like Monro, found it itchy, heavy, and stiff.

While Hammesfahr’s patents are rightly recognised, modern glass fibres started in 1932 when American chemical engineer Games Slayter (1896–1964) directed a jet of compressed air at a stream of molten glass and produced glass wool. This was refined and patented. In 1941 he was awarded a patent for producing multiple single fibres and ways of crimping them and producing yarn for textile purposes. While glass fibre as a dress material never caught on, after the war lampshades were popular in the UK, and in the sixties, curtains and fire blankets for a generation afraid of fire in the home and concerned about asbestos (we had both in our first marital home). A key development was coating fibres with a resin either for fabric or as a composite solid, which prevented the formation of microcracks. Glass with an unmarked surface is tremendously strong. From the 1950s, glass reinforced plastic (GRP) began to be used in chemical plants, especially for pipes and tanks (sometimes with a liner) being lighter and cheaper than metal and very resilient.

It was Indian-American physicist Narinder Singh Kapany (1926–2020) who coined the term fibre optics and pioneered its use for light transmission and images. Chinese-born British electrical engineer Sir Charles K Kao (1933–2018) received the 2008 Nobel Prize in physics for “groundbreaking achievements concerning the transmission of light in fibres for optical communication” during the 1960s and 70s. Sadly by then he lived in the US and suffered from Alzheimer’s so the prize money was spent on medical care.

The fibres are tubes of extremely pure glass in which a glass of silica and germanium oxides has been deposited on the inside by thermal decomposition of vapours of silicon tetrachloride (SiCl₄) and germanium tetrachloride (GeCl₄) in a hydrogen oxygen flame. This is then drawn out hot into fibres in which the difference in refractive index between the two glasses causes total internal reflection of the laser light pulses, minimising losses. In 1985, Ghanaian-American chemical engineer Thomas Owusu Mensah (1950–2024) at Corning Glassworks US improved the drawing process speed from 2 to 20 m/s, making the cost similar to copper cable, later getting it to 50 m/s and reducing the cost further.

Conclusion

The 20th and 21st century have seen too many developments to discuss in detail from the ultrathin screens of mobile phones to various kinds of heat- and impact-resisting ones now improving safety, double and treble glazing plus infra-red reflection for energy conservation, solar panels and its use in electronics. Electric- and hydrogen-fuelled furnaces are in increasing use. From the days of the Romans, there has always been some degree of recycling: nowadays it is a major feature of the industry, but one which offers severe social and technical challenges.

I remember the first time I interviewed a candidate for chartered status who worked for a glass company. At the time it was viewed as non-standard career, but I was impressed how much of it was fundamental chemical engineering, though with materials, processes, and conditions not generally taught in chemical engineering degrees, as I hope this brief history has shown.

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Martin Pitt CEng FIChemE is a regular contributor. Read other articles in his history series: https://www.thechemicalengineer.com/tags/chemicalengineering-history