Wedgwood Pyrometer By Pixii

Little current Wedgwood pyrometer signed "Pixii father and son Rue de Grenelle St Germain 18 Paris". The instrument measures 172x64mm and is constructed of bronze / brass. Named after Josias Wedgwood, maker of the blue porcelain that bears his name, who built it in 1782, this instrument is used to assess the temperature of refractory furnaces. Its operation is based on the shrinkage that the clay experiences by the action of heat (beginning of vitrification). This instrument consists of a brass plate called a gauge, on which are fixed three slightly inclined bars to form two truncated pyramidal grooves each divided into 120 equal parts which follow one another from 0 to 240. To use it, we take a small cylinder of clay previously dried in the heat of dark red, and calibrated so that it enters the gauge just at zero on the scale. The small clay cylinder is then carried in a refractory crucible which is placed in the medium whose temperature is to be measured. When it has taken its temperature, it is allowed to cool and it is put again in the gauge. It then sinks more or less deeply, by virtue of the shrinkage that it has undergone and that it has retained while cooling. Uncommon instrument, rare signature of "Pixii father and son".