A mother and her daughter visiting the Tracing the Conical Cup exhibition are standing next to project team member Loes Opgenhaffen. They are facing an upright display of cups cut in half, and the young girl is using a ultraviolet flashlight to look at one of the cups on display.

Loes talking to one of our younger visitors about the UV inked traces on display

One of the main themes of our exhibition ‘Tracing the Conical Cup’ is recognizing that there are many hidden traces of technology to be found on simple conical cups. The UV trace art display highlights some of the traces that can be found on the experimental pottery made by Caroline, and the touch table gives visitors the opportunity to handle experimental pots and 3D prints alike. The subject of these forming traces has been her focus over the course of several projects now and although she has written about them before in other places, the exhibition is a nice chance to share what the traces mean in a blog entry.

Each of the experimental cups on display was made using the wheel coiling technique. The foundation of the work that Caroline does is that there is a link between the precise technique that a potter uses and the kinds of traces left on the pot. In the case of the experimental cups here, that means viewers can often see fine rilling, stacked concavities, dragged inclusions, sponge wiping, incompletely joined coils, and torsional rippling.

Fine rilling

Fine rilling is defined by the presence of many very small and shallow lines of clay across the surface of the pot. These are mostly horizontal, but they may also be at a very low diagonal angle. Most importantly, they are parallel to each other, and if you can look at them across the whole pot then you can see that they spiral up across the whole surface. On Caroline’s experimental pots, you can see fine rilling across all of the surfaces, evidence of the way that Caroline’s hands applied pressure to the vessel walls and slowly worked upward. The impressions of her fingers overlap as they spiral up the walls, leaving behind this distinctive trace.

Stacked concavities

Like fine rilling, stacked concavities are some of the most readily visible traces that people recognize in pottery made with wheel techniques. Looking at both experimental and archaeological pots shows that these are usually nearly horizontal or just slightly diagonal so that they spiral up the walls of the pot. These traces are larger scale than the fine rilling, and it is helpful to consider them as the result of a potter applying pressure with their fingertips to the wall while the wheel turns the pot. These traces can be recognized in cross section as a series of shallow convex-shaped impressions one above another along the vessel height.

Dragged inclusions

Many of the archaeological pots that we study have inclusions mixed in the clay potters used (for more about what inclusions are, have a look at Jill’s discussion here), and half of Caroline’s experimental pots do as well. When a potter is working to shape a pot, inclusions are often pushed across the surface of the softer clay. As they are dragged along, the inclusions leave behind furrows in the same way that a plow makes a trench for planting seeds in a field. These drag marks are useful indicators of what direction a potter was wiping the clay. If the inclusions are all dragged horizontally across the surface, it’s a good sign that the potter was working in a single direction as is usual in wheel techniques.

Sponge wiping

Sponge wiping is visible in the very lowest area of the experimental pots. It’s very similar to fine rilling – lots of very small and shallow lines – but the key differences are that these appear in groups of lines, and that they can be vertical or diagonal. Sponge wiping appears on Caroline’s experimental pots on the inside near the base, and they are there because at the end of potting, Caroline uses a sponge to soak up excess water from inside of the pots while the pottery wheel is still spinning.

Incompletely joined coils

The wheel coiling technique used to make the TPW experimental pots requires joining coils together while the wheel is rotating. Often times, this means that small sections of the coil seams are still visible, especially on the inside of the cups. If we look at this trace in cross-section, the coils are each convex, one stacked above another. The point where these two convex surfaces meet forms a very sharp crevice which plunges into the wall of the cup. In many cases, the way that the trace appears when looking at the wall overall shows a pattern. The incompletely joined coils are irregular, small lines which do not parallel the other wheel-related traces like fine rilling, stacked concavities, or dragged inclusions.

Torsional rippling

One of the more unpredictable traces visible on the experimental and archaeological pots is torsional rippling. These traces are evidence that the pot was subjected to some kind of twisting force while the clay was wet. In the case of pots made with wheel techniques, torsional rippling appears most often inside of the pots on the lower walls or inside of a jug or bottle’s neck.

The recognizable feature of these traces is that they appear in groups of diagonal folds or pleats and can range from very slight tiny ripples all the way up to ripples which have stretched and torn the wall of the pot.