: bonsaipotter - Viewing Profile

Hello,
I'm looking for some advice on Stoneware clay slumping during firing.

I'm making bonsai pots which by design have a large flat horisontal base suspended in the air by 4 feet. During vitrification the stoneware glaze I use softens as it vitrifies and the floor of the pots can sag if they it is not supported.

I have a blog and posted a story on a test I did: http://bonsaipottery...ty-of-clay.html

As you can see from the picture the clay has matured but in doing so gravity has done its job. The clay is a local stoneware clay with some RIO included to give it a buff colouring. I'm only firing it to 1240C which is well below its nominated maturity temperature of 1280C. It was suggested that the RIO additive may be fluxing the clay and so I repeated the test with both the untinted base clay and the tinted.

 P1130402a small.jpg (83.95K)
Number of downloads: 25

As this picture shows there is no perceptable difference.

I am tempted to start a whole series of tests on all sorts of other clays that may be available but I only need 200gms of each to start with and that's not really practical. So the question is do all high and intermediate firing bodies slump during vitrification?

The other question I have is 'is there anything I can add to the clay to limit the impact of this characterisic?'. I have done some research into body formulation and the work done in the commercial ceramics industry to overcome this problem and it seems the answer may be yes, but does any additive actually solve the problem by simpoly elevating the vitrification temperature? I still want the body to reach maturity.

And so I have prepared some samples for a further test. I've taken 200 gms of my stoneware clay for 8 samples and then added 10gms of either Silica, Aluminium Hydrate, Kaolin, Magnesium Carbonate, Woolastonite, Rutile flour, Talc, Dolomite. I'm most hopeful of the talc test.
These are drying now and so will be a little while before I get to fire them to maturity. Can we predict the results? What will be the unintended consequences?

Looking forward to hearing from you.
Happy Potter