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The principal thinning, however, is done while the pot is still on the wheel after the completion of throwing. Around the circumference of many surviving Mill Green fineware jugs there is a slight horizontal line defining the upper limit of turning. Below this line clay on the walls of the pot was cut away as much as the soft tapered cylinder would allow. There is some evidence that after a drying period at least some Mill Green jugs were replaced on the wheel for further turning; this occurs when the jug is replaced on the wheel slightly off-centre to thin the walls. However, in the Museum of London's large collection of complete Mill Green jugs only two appear with off-centre turning.
The heavily thinned Mill Green fabrics needed to be strengthened in the firing process, and the potters used a firing technique which exploited the rich iron content of their clays.Vessels were fired in early reduction to create a ferrous oxide body flux sufficient to partially vitrify the fabric at temperatures around 900-950C. The result was a strong and generally impermeable fabric. Thin and hard walls of this kind will resist thermal shock by facilitating the rapid movement of heat throughout the pot, thus reducing damaging thermal differentials. This firing technique was used by the South Hertfordshire greyware potters at Chandler's Cross, Nettleden, Potter's Green and elsewhere and may well have influenced, or even been responsible for, the Mill Green technology. The significant firing difference between greyware cooking pots and Mill Green fineware jugs is simply that greyware producers maintained a reducing atmosphere throughout firing and cooling whereas the Mill Green potters reoxidised their pots. This subsequent reoxidation is clearly recorded in most Mill Green sherds: the distinctive grey/black carbon and ferrous oxide core is sharply delineated from the outer red reoxidised layers (see Kilns and Firing).
2. London tulip-necked balusters
The unusual height and narrow vertical axis of these fine jugs - about 390-420cm high and even higher when thrown - means that the lower walls must contain a generous amount of clay to support the upper part of the vessel during throwing. This additional clay makes the pot bottom-heavy and could create problems during firing. To avoid this the top 'tulip' neck and rim is thinned with the hand, and about a third of the way down the pot is thinned by turning with a tool which leaves a pronounced turning limit line(left). The turning was probably done on the wheel directly after throwing.
3. An unfinished Cheam drinking jug
Fig 1 shows a Cheam drinking jug with the body of the jug appearing much as it would immediately after throwing on the wheel, before the removal of excess clay by turning on its upper and lower walls. The turning or trimming stage appears to have been omitted in error, with handle and glaze being applied before firing in the kiln. Fig 2 shows a similar Cheam drinking jug after the conventional on-wheel turning which creates the biconical shape characteristic of the type of ware.
These stages of manufacture are demonstrated by three steps in the experimental throwing of Cheam-type drinking jugs:
In step 1 a flower pot shape is formed on the wheel.
In step 2, the top of the jug is collared and the neck and rim formed.
In step 3 (the turning phase, omitted in the jug illustrated in fig 1, left) excess clay is trimmed from the walls giving a severely angular profile. The jug is then cut off the wheel and placed on a board to dry somewhat before receiving its handle and bib of glaze.
'turning' and 'throwing'
Although the construction of medieval potters' wheels is uncertain much is known about medieval turning lathes, usually 'spring pole' designs. Wood turners manufactured 'treen': mainly bowls, dishes and cups or drinking vessels. In the 13th century the mazer was a popular drinking bowl usually turned from maple. The products of medieval metal turning are familiar in their variety. This production of domestic ware by 'turners' 'metal potters' and 'earth potters' links turning and throwing. The use of rotary motion turning on an axis is common to both potters and turners, and it is likely that the shared idea of 'turning' was adapted to the different materials of wood, metal and clay. To a medieval potter, the operation of turning his pots, if need be, would be would be part of normal practice. There is a possible linguistic connection between the terms 'throwing' and 'turning' (Dennis Krueger, Studio Potter, v.11,no1): the Old English word 'thrae' meaning twist or turn was expanded into 'thrawn' or twisted, and finally into 'thrown'. The terms 'throw' and 'turn' had the same meaning when referring to pottery making on the wheel. One may note, in passing, that turned spindle-back chairs of the late 15th century were known as 'thrown chairs', and that in the 20th century potters at the Marshall Pottery in Texas describe their work at the potters wheel as 'turning'.
removal from the wheel
Procedures for removing medieval pots from the wheel are largely conjectural. Vessels can be removed by 'cutting off': the wheel head is splashed with water and a thin, tightly twisted cord of gut passed through the water and beneath the base, then pulled through. This leaves the pot separated from the wheel by a thin film of water or slip, and in this state it can be pushed off the wheel and slid onto a waiting board. Noticeable finger impressions on a surviving Mill Green jug would seem to indicate the position of the hand in sliding off the piece just after throwing (left).Modern 'cutting off' techniques leave concentric or twisted cord impressions beneath the base, depending on how the cord is pulled. Medieval pots rarely have this effect and the cause of markings on the bottom is most likely due to pushing, moving or placing the soft vessel on rough surfaces, or possibly brief hand finishing with a rag or rib. It is may be that in some cases the base of the pot was removed by the use of a knife, either metal or a sliver of hardwood.
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