Porcelain is one of the oldest art forms - yes art forms - and has been around literally for thousands of years. However, the type of porcelain used here is - as you should know if you've perused other CooperToons art pages - is English porcelain which does not have quite the venerable history as Chinese porcelain.
The difference in the two sculptures is the one on the left is unglazed and the other is glazed. Glaze is in essence glass which is melted over the sculpture. But you don't take glass and melt it, no, no. You take a slurry of minerals and coat the slurry on the unglazed "bisque fired" sculpture. Then a second firing fuses the individual chemicals of the glaze formulation which then cools to form a glass.
You can also see a common characteristic of glazed porcelain on the (glazed) figure at right. That is the "crackleture" texture caused by the shrinkage of the porcelain at a temperature at which the glaze has solidified. Like much in fine art, what may have been considered an imperfection, becomes not only a "characteristic" of the art, but a characteristic of certain elegance.
This was actually a "study" intended for the porcelain sculpture. But sometimes studies are better than the finished product.