Jalte

Thanks for all your answers. I'm not sure I understand this; removable cottle made out of plaster or are you thinking about something like a plastic sheet around existing mould while casting (like drawing below)? Cutoff: existing plaster mould (blue), cast clay (red) and outer plastic sheet (yellow). I thought about this. Are we sure that actually what happens? It could also be while the clay dries the overflow stick to the top surface of the mould. See drawing below. Close-up cutoff: plaster mould (blue), cast semi dried clay (red) and surface where c

Yes that is what I do. I'll try that; you think I can put in a ring with a little larger hole and cut that? Like bottom image (cutting the blue part after casting) or how is the normally done? The cup is not completely circular at the edge. Thanks!

Yea that's maybe correct. It's not a necessity though; I have plenty of cups without and never thought about it (functionalisticly I think most common problems is to thin/hot surface (without handle) and how some cups directs the liquid back up (and out) when you pour it in — but that's just me). Thanks, Jalte

Okay; Sounds like it's generally better to just glazing both sides. I'll try that and see if the bend disappears. It is very much a aesthetic decision and it will look better only glazed inside so that's still the goal. Bought this one eight year ago in Japan and use it often, so guess it's possible to make something durable only glazed inside (it's also pretty much the overall look I'm going for). Thanks!

Yes; it is only glazed inside. Haven't tried glazing the whole cup so don't know. But I will try! (hope it's not that though; would like to keep only glazed inside (but if it is that, maybe I can try a different or thinner glaze) ). Thanks! (will post update in here but have to change heating element in the kiln before and very much hobby project so will take months)

As you both say yes maybe I should just embrace it (you got a point with the bottom lip); but in that case I guess it should be more prominent/just bigger — now it looks like a mistake / kind of mess up the curve. I use a knife to cut the edge and sponge afterwards yes. Maybe I should try to sharpen the knife (and be extra careful not to flex it). But I have to round the edge with sponge (I guess; can't really see an alternative (right?)). Thank you so much for helping !

Hi I'm making a slip-casted cup (porcelain, fired to around 1260°C (2300°F) , approx. 2mm (1/16 Inch) thick). Everything looks great but the edge are kind of warping/bending outwards and I don't know why. It first appears after it fired. See photos below. Anyone got any idea on what's going on? Thanks! Jalte