An old Porcelain Stone Mine

Unprocessed porcelain stone

It’s surprising to me how often archaeological discoveries seem to be made in Jingdezhen, but then I remember that wherever I walk in this place there are deep layers of shards beneath my feet.

A friend of mine was given samples from a recently found porcelain stone mine dating from the Five Dynasties Period.  Apparently the find has not gone unnoticed- professional antique makers have been secretly mining the site.  Luckily we have the chance to acquire some of this porcelain stone.

I’m often dealing with unfamiliar, traditional materials of which chemical analyses are lacking or unreliable.  In these cases, I usually create a series of line blends to get a basic idea of what I’m working with.  From those first tests, one can further refine glazes using more line blends and triaxials.

For this porcelain stone I created the following initial tests:

• Pure porcelain stone, crushed, milled and sieved.

• Porcelain body using porcelain stone and kaolin at 15-45%.

• Lime-fluxed celadon glazes:

  • Porcelain stone and 10-20% Er Hui (Glaze Ash)

  • Porcelain stone and 10-20% Wollastonite

  • Porcelain stone and 10-20% Whiting

Idealized “traditional” recipes are also based on two-component mixtures.  For glazes, porcelain stone was mixed with a flux like glaze ash.  For porcelain bodies, porcelain stone was simply mixed with a proportion of kaolin.

Usually a single line blend of either Whiting or Wollastonite could tell you a lot about a porcelain stone.  However, porcelain stone mixed with Glaze Ash or Whiting often results in fuming/carbon trapping, so I wanted to test each flux separately.  I usually also create Dolomite or Talc tests.

I also prepared two sets of test tiles for cone 10 and 12 firings.

Stones of all types can be used in glazes.  Joseph Grebanier’s Chinese Stoneware Glazeslists many recipes that use locally sourced granite.  And Brian Sutherland’s Glazes from Natural Sourcescontains a wealth of information on the subject.

A sledge hammer is used to break off pieces of the hard porcelain stone

A very hard mortar and pestle is used to further break down the porcelain stone.

The crushed porcelain stone is ball milled for four hours.

Even after milling, the mixture needs to be sieved.

After sitting and decanting excess water, the mixture is dried on a plaster slab.

Because I’m in a hurry, the mixture is further dried on the stove.

Porcelain body tests with increasing proportions of kaolin.

Fired porcelain body tests.

Fired porcelain glaze tests with increasing proportion of flux.