Clay and Body
The Marks on the Bottom of a Pot
The underside of a pot records more about how it was made than any other surface. Most of what is there is evidence rather than decoration.
Turn a piece of pottery over and there is usually more information on the base than on the whole of the rest of the pot. The foot is the one area that is deliberately left bare, and what is visible there is the raw fired body plus the accumulated traces of every process the piece went through.
Why the foot is unglazed
Glaze is glass. At top temperature it is liquid, and a pot glazed all over would fuse permanently to whatever it was standing on. The bare foot is a practical necessity, not a stylistic choice, and it has the useful side effect of leaving the clay body visible for inspection.
On some pieces a small unglazed ring or a set of three small marks appears inside an otherwise glazed base. Those are where the pot stood on refractory supports, allowing the glaze to run to the very edge without welding the piece to the shelf.
The spiral
A thrown pot that has not been turned often shows a spiral on the base, running from the centre outward. It is the record of the wire being pulled under the pot to cut it from the wheel head while the wheel was still moving.
A pot that has been turned will not show it, because the turning tool removed that surface. Absence of a spiral therefore indicates a finishing stage rather than a different making method.
The foot ring
A defined foot ring, a raised band around the outside of the base with a recess inside it, is cut at the leather-hard stage with a loop tool. It does three things: it lifts the base clear of the surface so the pot sits on a narrow, even contact ring instead of on a slightly warped flat, it reduces the weight of the piece considerably, and it gives the profile of the pot a visual foot.
The quality of a foot ring is a fair indication of the care taken over the whole piece. It should be even in width, smoothly cut, and free of a rough edge that would catch on a table.
Chatter, tearing and tool marks
Fine regular ridges across a turned base are chatter, caused by a tool skipping at speed on clay that was slightly too dry or held at the wrong angle. Torn, dragged patches indicate clay that was still too wet when it was turned.
Neither is dangerous and both are common, particularly on larger pieces where the timing window between too wet and too dry is short.
The base of a pot is where the making is least concealed, which is exactly why it repays looking at.
Colour and texture of the bare body
This is the only place the clay body itself can be judged. Its colour indicates roughly how much iron it carries and, together with the glaze colours, gives a strong hint as to whether the kiln was run with oxygen or starved of it.
Its texture indicates how much grog is in the body. Visible gritty particles suggest a coarse body chosen for large forms or for oven use. A smooth, close surface suggests a fine body chosen for smaller work.
Dark speckling through a pale glaze on the walls, incidentally, usually comes from iron particles in the body rather than from anything in the glaze, and the bare foot will confirm it.
Signatures and stamps
Potters commonly mark the base, either by incising initials with a needle tool while the clay is leather hard or by pressing a carved stamp into it. The mark is applied before firing, so it is part of the body rather than printed on top, and it cannot be added or altered afterwards.
An impressed mark is usually crisper at the centre and softer at the edges where the clay moved around the stamp. An incised mark has a raised burr along its edges where the tool displaced clay. Both are quite distinct from a printed or applied backstamp, which is what mass-produced tableware carries.
Kiln wash and shelf residue
Rough white or grey patches stuck to a foot are kiln wash, a refractory coating painted onto shelves to stop glaze drips ruining them. It transfers to pots that sat in the wrong place or moved during the firing. It can usually be ground off with a hone.
A patch of glassy glaze on a foot edge means a glaze ran further than it should have, and the pot had to be chiselled off the shelf. The resulting scar is often sharpened and left, and it is a reasonable thing to check for before setting a piece on a polished surface.
Putting it together
A base showing a clean foot ring, a smooth cut, an impressed mark, an open-textured body and three small support scars describes a thrown, turned, stamped piece made from a coarse body and fired standing on supports. None of that had to be stated anywhere. It is simply readable, and it takes a few seconds.