The body is Plainsman L215 (bisque fired at cone 06). The glaze is G2931K. There is good reason to glaze fire to cone 03 instead of 04. Although these commercial underglazes work the same the clay fired at cone 03 is stronger and a deeper red color. But best of all, the glaze is more transparent (because it has fewer micro-bubbles suspended in the glass). Cone 03 is also more tolerant of getting the glaze on too thick, at 04 it will turn completely milky.
G2931K - Low Fire Fritted Zero3 Transparent Glaze
A cone 04-02 clear glaze developed from Zero3 which in turn was developed from Worthington Clear. This employs frit instead of Ulexite.
The term Terra Cotta can refer to a process or a kind of clay. Terra cotta clays are high in iron and available almost everywhere. While they vitrify at low temperatures, they are typically fired much lower than that and covered with colorful glazes.