George S

Hi, yes I see your point, good guess! I visited a shop where I could inspect a large plinth/stool/table and it quite likely is a lowfire clay. "High fire porcelain functional ware in industry can be fired unglazed to maturity in a same shaped form, ie bowl fired in a bowl of a claybody that won't slump, then inspected for flaws and sprayed with lowfire glaze and fired off to glaze maturity." - This in particular is very interesting for me thanks for this info! Do you perhaps know where you read about the history of ceramic stools? Thanks!

Hi Peter, yes one could do as you proposed to increase the thickness on the bottom of the mould, but for my purposes I don't believe this would prevent the slumping.

Ah ok. The "wall" thickness varies from top to bottom of the piece, on the vertical walls the thickness gradually changes, while the top or bottom have a mostly uniform thickness respectively. While the piece is being casted the bottom wall builds the fastest therefore becoming the thickest wall. The vertical walls are tapered in thickness, this gradual change in thickness is mostly due to the rate I can physically fill the mold ( a bit slow-I have fairly rudimentary equipment.) During casting, this mold contains 80 litres of wet slip, lots of slip weight is compacting and encouraging the development of the walls towards the bottom. Towards the top of the mold, the walls are developing more so by how much moisture the plaster can draw out of the slip, without as much assistance from gravity. So if I were to flip the piece after casting, the bottom ( which would now be the top) would be thicker than the vertical walls. phew, gives my head a spin! does this answer your question?

I'm not sure what you mean by "seat"

Hi Jeff, thanks for the response! The support idea is a great one! The support would need to be quite cleverly engineered in my case, the bottom is not exactly open. And to make my life even more difficult it's quite important to me that the whole piece is black when seen from any orientation . Throughout this project I've been wondering why black kiln wash doesn't exist.

Hi, thanks for the response and welcoming! Actually I fired these works at 1200c, originally at 1300c but I decreased the temperature in a attempt to decrease the slumping. As for firing them unglazed and upside down, do you suspect this is how many commercially made ceramic "side tables" would be made? Worth a try, thanks!

Hi, I've been trying to make a side table in the shape of a "liquorice" , after the high fire, the top surface slumps considerably. this piece is about 60 cm tall and slip casted, I've seen ceramic side tables of a similar size and shape with tops that don't suffer from this amount of slumping. Does anyone know what changes I can make to avoid this slumping? Also, I've already made it so the top surface is somewhat covex prior to firing, this helps slightly but not much.