Compressive strength of cone 6 stoneware vs cone 6 porcelain

[Callum Donovan-Grujicich]

Hi, I have a question about the compressive strength of porcelain vs stoneware, if both clays are modelled with the same thickness and are both cone 6 clays. Which one would be stronger or better to use for large (4-5ft) sculptures?

Thanks,

Callum

[Callie Beller Diesel]

I think it depends on the specific recipes and why the compressive strength matters and exactly what you want your 4-5’ sculpture to be.

Generally speaking, a clay body meant for sculptures this large fall in the stoneware category, and those will give you the fewest working problems. A highly vitreous porcelain that’s very pyroplastic is going to move a lot with that amount of mass. But if you want it to warp in the kiln and create movement that way, that could be a major plus.  There are ways to make almost everything work, if you’re really bent on something specific. 

[Min]

Pete Pinnell did some research on comparing the Modulus Of Rupture (MOR) of about 50 different claybodies. Redart based smooth red earthenwares fired to maturity came out the winner in his tests. It's the bottom post in this link. What works for functional isn't necessarily the best choice for sculpture which wouldn't be the best choice for raku which wouldn't be the best choice for pit firing etc.

[Callum Donovan-Grujicich]

 

9 minutes ago, Callie Beller Diesel said:

I think it depends on the specific recipes and why the compressive strength matters and exactly what you want your 4-5’ sculpture to be.

Generally speaking, a clay body meant for sculptures this large fall in the stoneware category, and those will give you the fewest working problems. A highly vitreous porcelain that’s very pyroplastic is going to move a lot with that amount of mass. But if you want it to warp in the kiln and create movement that way, that could be a major plus.  There are ways to make almost everything work, if you’re really bent on something specific. 

The sculpture will be a heavy pyramid suspended on several fingers, so I was wondering which clay would be best to support a heavy mass.

[Mark C.]

You will need sculpture clay for  most sculptures -since heavy mass is a theoretical statement (how heavy, whats the support ,thickness and length etc) it not something we can answer well

are the fingers thick or thin? whats the weight pyramid? are the fingers straight up or at an angle?

[Callum Donovan-Grujicich]

1 hour ago, Mark C. said:

You will need sculpture clay for  most sculptures -since heavy mass is a theoretical statement (how heavy, whats the support ,thickness and length etc) it not something we can answer well

are the fingers thick or thin? whats the weight pyramid? are the fingers straight up or at an angle?

I don’t exactly know the weight or proportions of the sculpture, because I have not made it yet. I am just wondering which clay is stronger or can support a load better.

[Bill Kielb]

7 hours ago, Callum Donovan-Grujicich said:

Hi, I have a question about the compressive strength of porcelain vs stoneware, if both clays are modelled with the same thickness and are both cone 6 clays. Which one would be stronger or better to use for large (4-5ft) sculptures?

Thanks,

Callum

I don’t exactly know the weight or proportions of the sculpture, because I have not made it yet. I am just wondering which clay is stronger or can support a load better

It’s really hard to answer that because section design of the legs is critical. But maybe another way to look at this, porcelain is likely stronger in pure compression. Cast iron bridge structures are a testament to always keeping things in pure compression. Problem is it’s hard to do without introducing some moment into the connection or section. Which brings us to ............. porcelain usually slumps more during the firing. Generally it is more plastic than other clays as evidenced by anyone trying to make a large low lid. So in general (general being  the operative word) porcelain would be less desirable during the firing.

Not a great answer,  my best thought for now, but if I were a fighter pilot I would likely use the dead pan response “ It depends”