Mid Fire Porcelain Clay for slab on mold

[claclana]

Hello

I am wondering about the cone 5 porcelain, for pressing slab on big mold to be expose outside after firing (no frizzing environment)

I like it (in theory) because of the low porosity and low cone firing but couldn't find the lows...

 

it is very different from the porcelain cone 10, strength and work-ability? do you have some experience using it? what are the contras?

why would you advice me to don't use it?

 

also, I would like to use some very shinny iridescent glaze, white or transparent background (or something else) to bake no more than cone 6, also strong enough to deal with outside, can you tell me about this? or I am asking too much, from materials and you guys!?

 

THANKS!!

[Lucille Oka]

I cannot imagine any lows, as long as you have a perfect fitting glaze. Since you say there will be no freezing it should be fine. I would not make the vessel very thin however because outside ware receives a different type of treatment than indoor ware. It is exposed to little animals and winds that can knock it over. Try to keep the vessel in a protected area.

[claclana]

Thank you Lucille

 

the form will be post on a roof, i would prefer to do the sculpture and carve inside to empty it,

but I want to be sure is the same thickness all around, so planned to cast and use the mold for slab...

seems slower and more work but more secure too...am I wrong?

 

 

what max-minimum slab thickness do you recommend?

does this low temp porcelain crack-warping in the cooking as the cone 10?

 

 

Thanks!

[Lucille Oka]

I am not sure what you are trying to accomplish and the kind of a mold you are planning. If you are going to use slip in the mold or moist clay pressed into it. This I don’t understand. You can construct your sculpture in sections however assuring even thickness all around. All porcelain bodies are ‘special’ in that, even your best most careful construction can lead to cracks. It is the nature of the material especially when it is sculpted and ‘fussed’ over. The cracks may not show up until after the firing.

 

I can’t really tell you how thick the walls should be without knowing what you are doing and how big you are doing it. Rule of thumb for stability, 'the larger the work the thicker the construction'.

If you have never used low fire porcelain before I suggest trying it out. Sculpt some small objects, sculpt some large objects, apply additions and see what you get; make some thick and make some thin walled pieces. Do a smaller model of your design and study it before and after firing. You will then have a better understanding of the clay body that you will be using for your larger work.

 

Finally, I hope you will be using a mortar to attach the finished piece to the roof. I don’t know where you are planning to install the work, but be mindful of the heavy winds we encounter all around the world.

 

I hope this helps.

 

 

[Marcia Selsor]

Porcelain is not a good hand building clay at either temperature unless you adjust it using an aggregate. Porcelain is a dense clay body and warps. Molochite can be added as an aggregate to porcelain to open it uo for a better hand building body.

 

Marcia

[claclana]

thanks Lucile and Marcia

 

I thought about porcelain because of the low porosity for the outdoors, and I would prefer to be cooking at medium cone

I admit I am very intimidated by porcelain, in my experience (very limited!) mostly everything cracked or had fissure just at cone 04! which I don't get with my regular clay...

I plan to put the form (24"x 30") with metal structure (1/2"rods) bolted from inside (ceramic with weight on top of metal and epoxied) and extended/bolted to the roof (and pray!)