My initial porcelain body was made from a clay/shale mined at Ulan near Gulgong. This material is quite grey in appearance, and appears to be flecked with some amount of iron staining. Known as 'hard white', it is a true shale, with some crumbly quantities and other parts quite hard. It was crushed, passed over an electro-magnetic separator to remove the iron, and passed trough a 12 mesh sieve.
In formulating the clay body, the dry sieved material was blended with felspar and ground wet in a ball-mill for around 9 hours. During the grinding the body was deflocculated with soda-ash; apart from 'thinning' the wet mix to facilitate a more thorough and finer grind of the materials in the mill, the principal consequence of treating with soda is the cation replacement that occurs in the shale. This clay/shale carries a certain amount of flux in the form of potash mica, and it is the replacement of the K+ ions with Na+ ions that gives the clay a greater degree of plasticity, sufficient to make a reasonable throwing body. Without this treatment, the Ulan clay tends to be quite flabby, and hence not a good 'thrower'. This gives it a more limited usefulness from a potters point of view.
My circumstances have changed, and I am no longer able to use this material. This has been disappointing for me, as I no longer have the challenge of developing the clay into a better behaving and performing porcelain body.
The positive aspect of this change has been the move to a commercially made porcelain, Clayworks (Victoria) 'Southern Ice' porcelain. This is a very good porcelain clay, much better to throw than the Ulan clay, more tolerant of carving and alteration, firing whiter and being readily translucent! This is a truly fine porcelain, reminiscent of Chinese porcelain from Jingdezhen.