Indeed

This is a mug I made 25 years ago when I was experienting with using soda salt to replicate traditionanal salt glazing - without the polluting chlorine gas coming out of the chimney. For those unfamiliar with this old European invented technology; pots and other ceramic ware (like drainage pipes) are fired to the required temperature (1000 -1300 deg C) and common salt is thrown into the firebox. The intense heat splits the molecular bond of sodium and chlorine. The sodium makes a glaze with the silica in the clay and the chlorine escapes up the chimney. Sounds like an invironmentally dangerous thing to do. And it is, but actually on the small scale of a studio pottery the chlorine quickly oxidises and returns as acidic steam and safely falls to earth. Iron roofing cops it and rots out faster than usual. So soda has been used now these days and the exhaust gas is mainly harmless water. I dug the clay myself from the the outskirts of Whangarei NZ and added 20% ball clay and 10% potash felspar to stop dunting (cracking due to thermal stress - quartz inversion) and lower the silica content of the clay. It also made the clay more pliable and easier to use on the potters wheel. This pot was fired to 1300 Deg C. The internal glaze is based on the very traditional Japanese Tenmoku glaze that is normally black, breaking to rusty red where there is a thinner coverage. Salt glaze can make it look and run like treacle - adding warmth to what otherwise could be a more austere finish.