short castable questions

[josephjcole]

hmmm... we seem to have different definitions of fireclay, and clay in general. I've never heard of a synthetic fireclay. The material you seem to be describing sounds a lot like grog, which in fact is fireclay that is fired to a high temperature then ground up. I believe fireclay is a clay that is naturally more refractory with nothing synthetic added.

[Deleted]

Posted by josephjcole on Yesterday at 10:40pm

I believe fireclay is a clay that is naturally more refractory with nothing synthetic added.

That's my definition too.
But then any kind of clay has very small particle sizes.

[josephjcole]

Certainly you are correct that by definition clay has very small particle size. However naturally occuring clays have a wide range of particle sizes. My original point was that when you are purchasing powdered clay fireclay tends to have a much larger distribution of particle sizes sometimes up to 35 mesh. Where as kaolin is almost always sold as 200 mesh or finer. I know you said that thermal shock had other reasons other than particle size. I'm sure this is true, but in my experience, in ceramics particle size plays a very large factor.

[Deleted]

Posted by josephjcole on Today at 9:10am

My original point was that when you are purchasing powdered clay fireclay tends to have a much larger distribution of particle sizes sometimes up to 35 mesh. Where as kaolin is almost always sold as 200 mesh or finer.

Sorry, but for clay that is not the particle size.
Tat are just loosely connected clay particles, which will dissolve in Water.
If the clay is not purified there could be some sand too.
The real particle size is always below 0.002 mm.

but in my experience, in ceramics particle size plays a very large factor.

True, but to get bigger particles clay has to be fired and broken.
Thus it could also be grog.
In German grog is called Schamotte, which is translated to fire clay by dictionaries

[josephjcole]

Karl,
it sounds like we have different ideas as to how we define clay. For the record though when you purchase a bag of fireclay that is sold as 35 mesh it will not break down to 200 mesh in water. I suppose what exactly constitutes the larger particles depends a great deal on where the fireclay was mined, however in general the larger mesh does help with thermal shock and works well for mortars or brick making.

Sorry this thread seemed to become somewhat stand-off-ish... sounds like we both just have different backgrounds when it comes to clay, and therefor our terms didn't match up that well. The internet is prime for miscommunication.
take care
Joe

[Deleted]

josephjcole,

I have a technical background.
The International Organization for Standardization ( ISO ) was founded to provide a base of technical definitions.
ISO 14688 deals with Identification and classification of soil.
www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=25260
www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=34082

[Deleted]

josephjcole,
what you are describing could be powdered mudrock.
Clay minerals can become mudrock under pressure over a very long time.
But that is not longer clay in the technical definition.

[Deleted]

Claystone
www.britannica.com/EBchecked/topic/120751/claystone

[josephjcole]

Karl,
thanks for the link on Claystone, I've never heard that term before... always something new to learn!

We certainly do have different backgrounds! I make my living selling woodfired pottery, so although I've done a lot of testing for clay shrinkage, vitrification, and particle size, all my training has been hands on and not especially technical.
take care
Joe