Book: Ceramics - Art or Science? Author: Dr. Stan Jones

14. Early Scientific Applications and the Role of Pottery Manufacturers

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14.3 Worcester

There were two notable makers of ceramic scientific wares based in Worcester. One was the Grainger factory that in 1849 was making very glassy funnels using their Parian-like semi-porcelain, and a catalogue of 1854 illustrated laboratory equipment including funnels, pestles and mortars and galvanic jars.

The second was the Worcester Porcelain factory that, from the start of operations at their Severn Street factory around 1788, carried out continuous research on improving the production process and improving the body pastes. As early as 1850-60, experiments were carried out to produce the ceramic cores for very early high-stability resistors, and high temperature alumina ware appeared in their catalogue around 1860. In 1900 George Hancock, the company chemist, set up a specific research laboratory to devise scientific ceramics. F. E. Wooldridge who had studied laboratory porcelain production in Germany succeeded him in 1913. Soon after the start of the First World War in 1914, the British government asked Worcester to help with the war effort by developing a replacement for scientific, hospital and laboratory porcelain that was imported mainly from Germany, including crucibles, funnels and beakers. However this was an onerous task as little information on the manufacturing process was available outside Germany. It had to be high-fired, heat and shock resistant so it was capable of being heated to red-hot and then plunged into cold water without cracking. Extensive research work took place to find a body that would be completely vitrified and non-porous, and would be refractory at high temperatures. Glazes had to devised that would not crack with rapid temperature changes, and were highly resistive to chemical reagents. Their hard-paste porcelain body was based on the conventional China clay and China stone, but was quite difficult to produce. To make a ceramic that is resistant to thermal shock, the microstructure of the body has to be just right, and should consist mainly of mullite crystals. Of the porcelain constituents, clay, feldspar and quartz, no free quartz should remain. This is necessary to avoid the problem that any remaining quartz would change phases several times with increased temperature making the body more fragile. The body needed to be fired at a high temperature – the 1300 ºC normal vitrification temperature is inadequate - and 1450 ºC is needed to convert all the quartz to mullite. This produces a completely non-porous body. It was improved over a number of years and by 1923 it was highly resistant to fracture, impermeable to 1350 ºC and the glaze resisted softening for four hours at 1100 ºC. A cheaper version called Sillax was produced for school laboratories in 1931.

Worcester laboratory wares after 1931 - courtesy Worcester Porcelain Museum

Worcester laboratory
wares after 1931
- courtesy Worcester
Porcelain Museum

Just prior the outbreak of the Second World War in 1939, scientific and laboratory porcelain was still being imported into Britain from Germany, so Royal Worcester was asked again to assist with the war effort. In 1938 Royal Worcester had the only hard porcelain plant in the UK, which made the company well placed to help. Initially they were asked by the Ministry of Aircraft Production to support Steatite and Porcelain Products Ltd. of Stourport, which was the company that produced insulators and resistors for aircraft radar and radios. This work quickly came to represent a third of the Worcester factory capacity. Shortly after, early in 1942 they started producing the resistors for Welwyn Electrical Laboratories Ltd.

High stability resistors made by Worcester - courtesy Worcester Porcelain Museum

High stability resistors made by Worcester
- courtesy Worcester Porcelain Museum

These two product ranges employed some 200 people (mostly women) initially working two twelve-hour shifts. Worcester still had the small laboratory associated with the hard porcelain development work at the top of an old mill building in its main factory in the centre of Worcester that was reactivated. The workload on the Worcester chemists grew to carry out further experiments on new fireproof bodies and glazes, so the laboratory had to be expanded in 1943. One such material developed in late 1944 was an alumina body for spark plugs, which they produced at a rate of 30,000 per week. So the Worcester factory was virtually taken over by the Ministry of Aircraft Production during most of the Second World War.

After the war the focus of production of high specification industrial ceramics turned to more peaceful laboratory and school wares. The Laboratory Porcelain and Alumina Ware product list for 1960 contained: beakers, basins, pots, crucibles (various), filter discs and cones, funnels, mercury troughs, mortars and pestles, and insulated tools.

Spark plug bodies produced by Worcester - courtesy Worcester Porcelain Museum

Spark plug bodies produced by Worcester
- courtesy Worcester Porcelain Museum

Worcester first floor laboratory around 1950 - courtesy Worcester Porcelain Museum

Worcester first floor laboratory around 1950
- courtesy Worcester Porcelain Museum

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