Pyrometer - 1782
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Pyrometer
© Wedgwood Museum
Used to measure the shrinkage of clay during firing, indicating temperatures and heat within the bottle oven. During firing clay shrinks in direct proportion to the heat inside the kiln and therefore it is possible to measure the shrinkage in the graduated channels and calculate the degrees of heat. These were measured in ‘degrees Wedgwood’.
Used to measure the shrinkage of clay during firing, indicating temperatures and heat within the bottle oven. During firing clay shrinks in direct proportion to the heat inside the kiln and therefore it is possible to measure the shrinkage in the graduated channels and calculate the degrees of heat. These were measured in ‘degrees Wedgwood’. Josiah Wedgwood I was elected a Fellow of the Royal Society in 1783 for this invention.Two channels, rectangular in cross-section, arranged side-by-side to form a composite unit, thereby affecting an economy in the quantity of brass needed for its construction. One channel covers the range 0 to 120, the other 120 to 240 ‘degrees Wedgwood’. These were specially made for use by Wedgwood by specialist brass dealers.The words ‘thermoscope’ or thermometer for measuring high temperatures are also used as terms to describe this invention. When Josiah Wedgwood commenced his career as in independent potter in 1759 the only way the temperature inside the ovens could be judged was by careful observation of the colour of the flames and by the skill and experience of the kiln men. Success or failure of the firing of a kiln was the responsibility of the kiln master, who was frequently one of the highest paid workmen at a factory. Josiah Wedgwood’s scientific mind made him search for an alternative to this guesswork method of determining heat inside the kilns, and soon he was experimenting by placing trial pieces in different parts of the ovens to observe the affect of variations in temperature which arose from the location of the trial. In 1780 Josiah experimented with a red-burning clay, pieces of which were withdrawn at two hourly intervals whilst the temperature was still rising, and the colour changes observed. These trials suggested to him the concept of a thermoscope where the colours could be matched against a set of cylinders fired at known temperatures. Sir Joseph Banks observed in 1781 that it was difficult to evaluate colours and Wedgwood turned to the idea of using the shrinkage of clay to determine the temperature. Josiah’s first sketch for his pyrometer, which he always referred to as a thermometer, is dated 1st January 1782. Once the instrument became known it met with wide demand from potters, as well as being used for a range of other scientific purposes. Wedgwood began by having the pyrometer manufactured in brass which was an expensive metal in the 18th century, and by the autumn of 1783 he was experimenting with their manufacture in stoneware. From 1786 buff stoneware pyrometer sets were boxed and available for sale. Additional clay cylinders were available from the Etruria factory. An instruction booklet was available by 1784, with a further 1000 copies translated into French published in 1785 and 500 copies in German in 1786. On 9th May 1782 Wedgwood’s paper entitled ‘An Attempt to make a thermometer measuring the higher Degrees of Heat, from a red Heat up to the strongest that a vessel of Clay can support’ was read to the Royal Society in London. Eight months later, proposed by the architect James ‘Athenian’ Stuart, Josiah was elected a fellow of The Royal Society, the highest scientific honour of the period. He presented further papers to the Society in 1783, 1784 and 1786, about improvements and amendments to the pyrometer.
- Type of object: Non-ceramic objects/tool
- Mark: Impressed with the scale of degrees and J. WEDGWOOD & SON F. H.
- Year first produced: 1782
- Material: Brass
- Accession number: 11389
- Dimensions: 173 mm (length), 65 mm (width)
Related people
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Josiah Wedgwood
Designer
Josiah Wedgwood - Designer
Josiah was born in 1730, the youngest of twelve children born to Mary Wedgwood and her husband, Thomas. His father was a potter who lived and worked at the Churchyard Works, Burslem. This town was still connected by rough roads to the other five towns which made up the area of North Staffordshire known as the Potteries. By the time of his death, Josiah Wedgwood I not only improved the variety and quality of pottery produced, but he also opened up the area as an important centre of commerce with the rest of the world through his involvement in the development of canal and road networks. He went on to become one of the most influential ceramic manufacturers in the world, and earned the title 'The Father of English Potters'. His direct descendants are still involved in the factory which bears his name today. Much of Josiah's development as a successful businessman, philanthropist and potter can be accounted for by the ill fortunes he suffered. At the age of 9 when his father died and he had to abandon his formal school education in order to work in the family business. Then at around eleven years old he contracted smallpox and was left with a knee-infection which constricted his use of the kick-wheel on which the pottery shapes were formed. From that time onwards he focused on affecting the perfection and marketing of Burslem's main product. Another spur to Wedgwood’s success was his growing affection for his distant cousin, Sarah whom he had met at the home of his wealthy uncles, John and Thomas. Whereas Josiah came from a poor background, Richard, his future father-in-law, was a prosperous cheese-merchant from Cheshire who apparently insisted that the young potter achieved a certain level of wealth before he could marry his daughter. Wedgwood entered partnerships with other potters, most notably Thomas Whieldon, and established himself as an independent potter in 1759. He moved to superior premises at the Ivy House Works where he perfected his Queen’s ware body and then to the Brick House Works. His reputation was rapidly spreading farther afield and finally, Richard was convinced of his suitability as a husband for his daughter, Sarah. There is no doubt as to Josiah’s love for Sarah when, on the eve of their wedding in 1764 he wrote to his partner, Thomas Bentley: 'I yesterday prevailed upon my dear Girl to name the day, the blissful day! When she will reward all my faithfull services and take me to her Arms!'.
