The likely small orifice diameter may suggest that this is in fact a group D sherd, but without the rim I cant say for sure. While the only decoration listed here is an annular line located at the neck-shoulder break, there are also several subtle undulations or furrows on the external neck, indicative of a coil-building approach to the neck or of true decorative elements. The majority of the polish has abraded of the external surface, but 10% remains in different places, particularly in the shoulder area. Numerous coarse send and even some grit particles are visible in the breaks, in addition to the medium sand mentioned above. Rotational striations are visible on the external surface only. While the first core band is black, its most internal portion is highly mottled black /brown, perhaps related to the not-so-black color of the internal surface. Alternatively, the internal surface could be 80% covered with light yellowish brown corrosion, but I believe that increased oxidation towards the internal surface has turned it lighter than the black/brown core.
From Interior to Exterior