From Slip to Bisque in a Day? 

Yep, exactly. Slip cast in a mold and wait a fixed time (mine are about 25-30 minutes) and see how thick it is, then try again if you want something different. (Although for this kind of pottery, "exact" usually isn't too important given the handmade nature.) The other variable besides time is actually water. In particular the water in the mold from the last casting. So most production potters will use a fixed schedule with their molds (like once a day) just so it's a known quantity.

@@PotterybyKent that’s very intuitive and I really appreciate your reply! Because of your channel I am buying a 3D printer and getting into ceramics

That's how I started and taught myself - lots of RU-vid and Instagram! There's a lot to learn, but I've really enjoyed it.

Thanks for the ideas! I've also been thinking about ways to simplify adding the holes. The idea of pins in the mold is an interesting one - however it won't really work that way. The slip will still settle out around the plastic so the hole wouldn't be open (it would however be much thinner). There are ~2 states of fired clay. The final firing (glaze firing) vitrifies the clay to maturity and is at that point ceramic (so non-absorbent). Before that with the bisque firing, the piece is still porous and useful in getting the glaze to stick (the bisque sucks the water out of wet glaze). I don't think it is that absorbent though so probably wouldn't work for slip. I'm not sure I follow the spots of glaze part.

@@PotterybyKent My assumption was that it is possible to fire clay so it has enough open porosity to suck water out of slip for slip casting. I was thinking of the use of ollas for evaporative cooling. I was assuming that the slip wall forms mainly by selective permeation of water, leaving the clay behind, rather than settling as such--no water flow, no deposition of clay. Glaze spots were intended to be a way of selectively rendering a fired clay surface impermeable, so as to prevent slip deposition. But, like, a smear of lots of things could do that job. Wax, silicone RTV, etc depending on other requirements. If even bisque fired clay isn't permeable enough to deposit slip, that might not be a showstopper if a clay mold would actually be advantageous. One could put in pore-forming additives, or stuff to absorb water, if needed. The only reason I thought about clay vs plaster is because I think the pins might need to be somewhat close fitting to prevent slip from leaking out, so if one went to the effort of getting a somewhat precise fit one might want a more robust mold that could last a bit longer.

Ah I understand. Slip is a bit complicated for sure! The capillary action of water being sucked into and through the plaster is the primary mechanism. However water will also transport through the deposited slip as well, etc. Earthenware is porous like bisque (they're fired to similar temperatures). You couldn't use raw clay as it would just rehydrate. I have seen bisque used for molds with throwing clay being pressed into it. My guess is that the plaster just has been tuned specifically for this purpose (it isn't regular hardware store plaster). I don't think getting pins to be tight fitting in the plaster would be a big deal. And even if there was a bit of flash, it would be easy to clean up. The other trick with using something that has been fired is you'd need to account for the clay shrinkage so getting the hole the right size (and consistent) would be a trick. But I like the idea - it might be worth doing some tests to see what kind of holes are created. My other thought building off this would be to have a structure inside the mold (submerged in the slip) that could then be removed from the newly formed pot. Maybe something 3d printed.