The wax for the head would be very thin, no more than 3 mm. One of the first dolls that portrayed a baby was made in England from wax at the beginning of the 19th century. Porcelain became popular at the beginning of the 19th century. Porcelain is made by firing special clays in a kiln at more than 2372 degrees Fahrenheit. Only a few clays can withstand firing at such high temperatures.
Porcelain is used generically to refer to both china and bisque dolls.
China is glazed, whereas bisque is unglazed. Germany, France, and Denmark started creating china heads for dolls in the 1840s. China heads were replaced by heads made of bisque in the 1860s. Bisque, which is fired twice with color added to it after the first firing, looked more like skin than china did. The bebe, first made in the 1850s, was unique from its predecessors because it depicted a younger girl.