The Plymouth Factory

Most writers place the factory in Coxside, near the waterfront.  It was previously thought that the factory was on the site of what is now the licensed premises known as the China House.  Worth made a case for High Street, nearer Cookworthy's home.  Archaeology has not been able to produce any evidence for either site.  Cookworthy's letters (see experiments) may suggest that the factory was in the Coxside storehouse, and there has been no archaeology on that site.  There is a mug in the British Museum dated March 14th 1768, but this was experimental, proper production had not started by January 1769.  Richard Champion was one of the investors.  In total some 2000 to 3000 pounds was spent at Plymouth (Hurlbutt).  The factory was beset with problems.  The china stone was of a variable quality.  Cookworthy's experiments with firing with coal were a failure and he had to use expensive wood, which continued to be used at Bristol.  Hard paste porcelain requires at least two firings in the kiln.  The first, at 900 degrees centigrade, is the biscuit stage.  Any under-glaze painting is added and the piece is glazed.  There is then a reduction firing (also referred as a glost firing) at a temperature of some 1400 degrees centigrade (during which the porcelain naturally shrinks, by about one sixth), which was difficult to control.  Some of the pieces show smoke staining.  The smoke staining may have been caused by the use of Admiralty wood, which would have contaied salt and produced much smoke.  Pieces often became distorted or cracked in the kiln, plates collapsed, impurities can be seen in the paste and grit is sometimes found of the bottom (or even on the inside) of pieces.  Some of these problems would not be solved until the later phase of Bristol.  Another problem was oxidation, resulting in the under-glaze decoration becoming uneven in color, or even black.  The solution was to use a low flame wood to build up the temperature, then switching to a high flame wood, with the flames licking around the saggars.  For over-glaze colours at least one further firing was required in an enameling kiln (also known as a muffle kiln). Spiral wreathing occurs on both Plymouth and Bristol pieces, that were thrown on the potters wheel.  The wreathing is in the direction of the potter's fingers.  It is due to the nature of the paste, not lack of skill of the potter.  Another problem was crooked handles, this is due to the porcelain unwinding during firing.  To avoid this it is necessary to put the handle on with the top in advance of the bottom (in the direction of throwing), this was done with the later wares.  The Plymouth pieces often show grit stuck to the foot-rim (specking), caused by problems with the saggars.  It would have been a simple task to remove it, why was it not done? One success that Cookworthy had, was the glaze he developed.  Made from similar materials to the porcelain it bonds closely to the body on firing.  It is hard and has a glassy appearance.  With the lead glaze, of soft paste porcelain, enamel colours sink into the glaze and become glossy.  This does not happen with Cookworthy's glaze and the enamel colours remain matt. To solve the problems Cookworthy needed potting expertise and more capital.  These were not to be found in Plymouth, so in 1770 the business moved to Bristol, and Plymouth closed down.  It has also been suggested that by 1770 the factory was succesful and needed larger premises.  It is known that Cookworthy gave up the lease on his mill in that year.  The final Plymouth firing of the Plymouth kiln occurred on 27th November 1970. See also Cookworthy's experiments and a Plymouth kiln.