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Convex or 'sagging' bases
The purpose of sagging bases on medieval jugs is imperfectly understood, although some conjectures seem to apply.
The first is a connection with tripod pots. Tripod pitchers let a person avoid the need to lift a large and heavy jug when it is used for filling vessels at the table: the jug pours easily by being raised on its two front peg feet. The sagging base jug can be viewed as a development of the tripod base, to some extent replacing it. A large jug with a sagging base has a low centre of gravity when filled and will remain stable on a flat surface. It can be poured and manipulated at table simply by rolling it forward on its convex base, without the need of specially added feet. A large replica sagging base jug, used over a period of some weeks, demonstrated convincingly the effectiveness of a jug of this construction as a container used for pouring - into modern tumblers, and also into the shallow, cup-like treen vessels of the period .It is possible to hold the cup in one hand and pour the jug with the other, a difficult feat with a big, heavy flat-bottomed jug.
Sagging bases also occur on cooking and other pots clearly not intended for use on a flat surface. In the case of cooking pots, it is likely that sagging bases contribute to the reduction of thermal shock since convex base shapes are much more resistant to cracking than flat shapes. A sagging base is also likely to have a practical advantage when placed in a larger vessel or cauldron of boiling water in the process of cooking. It would seem that sagging base jugs were multi-functional items, intended to cope with a variety of situations: storage, cooking, carrying and use at the table.
The sag itself is easily made. In the pre-leather hard stage, with one hand holding the pot and the other inside it the bottom can be gently pushed out by using a circular motion with a damp piece of wadding or a rag, moving from the inside edge towards the centre. In some cases a modest sag can be made by trimming away excess clay on the circumference of the bottom edge of the base.
basal thumbing
Basal thumbing had a tehnical function in addition to any decorative enhancement there may have been. One of the continuing problems in managing medieval kilns is the arrangement of the pottery stacked inside them. For the most part, medieval pottery was fired upside down. In a firing containing glazed ware a potter must take precautions to ensure that the melting glazes do not flow from one pot to another and fuse them together when they are cooled. Surface contact of pots in the kiln stack must be kept to a minimum to prevent the pooling of glaze from forming a bond between the vesels.
A thumbed base reduces the area of contact between pots to the points at which the tines of the thumbing touch the rim of the pots above them (see left). The addition of a thumbed footrim, whether complete or partial, creates an area between the pots where the glaze flow can spread freely without joining them together. A complete thumbed footrim is not essential since the rim of an upper pot will touch those below only at three or four places on its circumference. Vessels with grouped thumbing or with irregular projections will distance the pots placed on them from any glaze running onto the base. As technical advances in glazing, kiln construction and firing practice become apparent in the late medieval and post-medieval periods, thumbing on the bases of jugs virtually ceases.
A recessed base or footrim occurs on some medieval pottery, especially London-type Rouen copy jugs and large tulip-necked balusters. Although it is rarely clear exactly how the recesssed base on a particular pot was made, either of two general procedures seem to have beeen followed. The footrim can be cut into the thickened bottom of the base at a pre-leather hard stage, using a sharp wooden or metal tool. Alternatively, excess clay around the base can be pulled up and folded over around the circumference of the base, pressed down and trimmed evenly with a tool. The second method probably saw frequent use. Like a thumbed base, a recessed base helps reduce the contact between glazed vessels in a kiln stack and keeps kiln losses from glaze fusing to a minimum.
Recesssed bases sometimes consist of nothing more than an indented or hollowed out and depressed area in the centre of an otherwise flat base. The function of the depressed area is, once again, to contain glaze runs without joining the pots together in the stack. This feature is common on Brill/Boarstall balusters.
last page of Base
Further reading: Newell, R.W., Thumbed and Sagging Bases on English Medieval Jugs: a Potter's view, Medieval Ceramics, 18, 1994
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