Questions on a DIY Slumping Mold


Hey Glassies. Need some expert advice. I just took the slip molding class and I’d like to build a glass slumping mold out of slip. I’ve made molds before so I’m good there but I don’t know anything about clay. Should I be using a high fire or low fire clay for a glass slumping mold?


I would be inclined to use the mid-fire (Cone 6) stuff. While low-fire is fired to Cone 04, I personally feel like you’d be surer of a stoneware clay never starting to melt on you.



I would personally use cone 6 but it probably doesn’t matter as long as you remember what you used.


Just an FYI mid fire slip is rare for slip casting. Porcelain slip is the only mid fire slip I recall using and it was for dolls and specialty items. If you go to a ceramic shop it’s all low fire.

Slumping and draping firing temps are way lower than what low fire slip is fired at. When I make glass molds I use low fire.

I hope you have a great weekend, I will be out of the loop for a bit.

Anita Willis


We buy a Cone 6 slip from Trinity. I’m assuming it’s stoneware, because the Cone 6 porcelain is really weird if you’re making pots with it.


I am thinking DMS took up cone 6 for 2 reasons.

  1. they had not a clue what the norm was for general slip cast

  2. they could use cone 6 glaze since that what DMS has. The items I’ve seen done look awesome.

Low fire glaze come on smaller size and are cheaper.

I bought some cone 6 slip to give it a try. Please fire the big plate on top the big kin. It needs to be fired in a flat surface or it will warp or crack.


I already had my own glazes which were cone 6 so I do cone 6 slip but it is a pain to find what I need when most of slip casting is low fire. And yes it is more expensive. For slump molds it’s probably not going to matter much either way. I know of another Makerspace that was probably going to go with low fire as their standard last I checked.


It fits into our normal firings, and doesn’t require slip-casters to have to put info on every single piece that gets fired. OTOH, the whole “having both” has me pausing and getting info before I’m willing to fire a glazed slip piece at Cone 6. Melted bits are no fun.


Thanks for all the feedback. In the end Trinity Ceramics told me to go low fire for glass so I bought both low fire and a cone 6 and will experiment. Will let you know what works best!


And, since you won’t be glazing a slump mold, you’ll only be sending through the bisque firing, which is a good temp for both bisque and Cone 6. Low fire doesn’t go any higher, so you’re golden.