Illustrated is the base of a chawan that is in itself a bit unusual, the form of the bowl is kutsu-gata, also not round(ish) and as you can see, the kodai is a bit ovoid and though not easy to orient in this photo, in some respects looks a bit like a seated Daruma, narrower at the top and wider at the base. The wonderful tsuchi-aji and wad shadows are highlighted inside the depression where the foot was excised and is now surrounded by a wet, gray ash from the wood firing process, ash runs toward the footring as gravity and promethean fire has added to the iron and Shino glazes Tsukigata used prior to firing. Together with the well cut foot, running ash and glazes the potter has added more decoration to the bowl leaving his fingerprints cemented into the surface of the pot where he held the bowl while he was glazing it.
I realize pointing out the anomaly of the way the foot was cut and addressed seems a small, almost insignificant detail but my personal belief is that the details make the pot, these same details authenticate the pot and these details are exactly why a potter builds a reputation over sometimes decades and decades of work. In the end, a potter like Tsukigata Nahiko is sought after because collectors flock to those details, no matter how small and when you add them all together and manage to fit them all on one small bowl it can be magic.