Tevilla for Glazed Chinaware
I heard that the process of glazing chinaware has developed recently and is not identical to the process mentioned in the poiskim. According to this Shmeuoh, the layer which is covering the plates etc. is made out of a very different material than conventional glass and consequently the requirement of tevilas Keilim must be revisited. Apparently, there is now no longer an obligation to toivel, even without a berocho.
I am not aware of any change in the age old process of making porcelain, china, and other clay/earthenware based vessels. These are considered “klei cheres” earthenware vessels which are exempt from tevilas keilim. However, most of these vessels made today are coated by a thin layer of liquid glass which dries on to the surface. According to some poskim this gives the vessel the status of glass vessels which require tevila. Even one who is stringent would not make a bracha on this tevila.
The Aruch Hashulchan notes that common practice is to be tovel even non glazed porcelain. He explains that this may be due to confusion as to whether it has a glass coating or not, and so the custom became to be tovel. This is unique to porcelain which has a smooth finish even without a glaze, as opposed to regular pottery which is completely exempt when without coating.
See She’elas Yaavatz 1:67; Pischei Teshuvah, Yoreh De’ah 120:29
Aruch Ha-Shulchan 120:29; Ben Ish Chai Matos 7.