Porcelain

[Pamela Sinclair]

I continue to have problems with surface bubbling. Sometimes it is a very fine bubbling just under the surface. I am stumped - sometime it happens and sometimes it doesn't. I am using a Grolleg cone 4-6 clay from Clay art. The main glaze is the cone 6 majolica from Mastering cone 6 glazes, I also use their firing schedule. I have been having this ongoing dilemma for over a year. The pieces are medium to large covered jars with smooth surfaces.  I would love any mentoring concerning working with porcelain. I have been working with clay for many years and this is how I make my living.

[Chris Lively]

Pamela
I also left you a message on your page, but here is some further information on your problem that might help. http://www.lagunaclay.com/support/bloating-and-blackcoring.php

[Norm Stuart]

The prior studio facilitator bought some cone 4 porcelain which bloated at cone 6, even after a hard bisque with a 20 minute hold.  Something in the clay decomposed in the heat at cone 6. The more you fired those pieces the more they would puff-up and warp like a Pillsbury dough boy.

The piece below was covered with a Cone 6 Tenmoku. Each of these pieces is a thin slab of white porcelain, less than 1/4" thick which had a very angular look. But after firing you can see all the pieces have puffed-up like a pastry and rounded out, with the base warped into a curve.

I'm starting a piece with what I think is Laguna WC-437 Frost Porcelain, but it's labelled Cone 5, so I will be interested to see how it fires.

I've also experienced bubbling problems with porous cone 10 clay with a cone 6 glaze fired at cone 6. The clay never densifies, so the glaze infiltrates so deeply into the bisque, vertically as much as 3 inches within the bisque, that the glaze reaction off-gases all through the piece with pinholes everywhere.

[Pamela Sinclair]

Hey Norm, Thanks for the reply. I have tried refiring pieces with slight glaze anomalies and they come out with bubbles surfaces.  I continue to be amazed at the myriad ways of clay . . .

I am about to fire another load of the cone 4-6 porcelain at a slightly lower temp - I live in fear and trepidation!

[Norm Stuart]

We have a 2005 copy of "Ceramic Faults and Their Remedies" at our studio. It's helpful.

After showing this book to a artist raised on Harry Potter he said, "Wow! This is like a book of Curses and Counter-Spells."

http://www.amazon.com/gp/product/0713671912/

[George Lewter]

Looks like a good resource. I just ordered a copy.