From the Ground Up
New Work From an Old Landscape
Steve Harrison investigates native porcelains developed from
Australian Bai-tunze of the Southern Highlands of Australia.
article details my recent research in the use of local materials –
specifically, woodfired porcelain and proto porcelains made from the native
porcelain stone (bai-tunze) of the old Mittagong Shire. During the development
of this work I intended to make a 100 per cent local product. In this
regard I have to admit that I have failed, as one of the clay bodies contains
one per cent of bentonite sourced from outside the Mittagong shire. In
a time when international cultural boundaries are being smudged or collapsed
by free trade agreements and globalisation, one result is that simple
consumer items such as ceramics are conceived in a design studio in Europe
or the US and produced in a factory in China, then shipped to every first
world country in the developed world. The result is less choice, less
individuality. This work is my attempt to produce a fully local product
– with all its limitations and faults, and all its local character.
The French have a word, ‘terroir’ that expresses some of this
quality. Better porcelain clays can be bought from the local art supply
shop. However, they are made from mostly imported ingredients, from all
over the world, New Zealand, USA, Europe, Canada and China, at least the
water used is Australian. The net result of this international roast is
that everyone’s work has a sameness about it. What was once exceptional
has now become commonplace. Globalisation has resulted in a situation
where we are spoilt by the availability of excellent materials –
the best of each class of ingredient is available here now from every
market on the globe.
For all its faults, and I am sure that there are many, this work has
a character imposed on it by my choices of technique and my ability to
extract suitable materials from my local geology. At this point this is
the best I can do with what I have discovered. I have used and developed
some of the limitations such as the impurities in the raw material to
give an exquisite surface flash that is enhanced by the woodfiring process.
Usually rich red flashing and translucency are mutually exclusive qualities.
However, in this case I have managed to coax both from my materials.
From one point of view this work can be seen as an intellectual exercise,
a strike against globalisation, and that might be true and all that there
is to it, until you see and handle the pieces. This work is special to
me, it has the most wonderful quality, a juicy beauty that elevates the
soul. The play of light off the glaze and clay surfaces and through the
translucent clay bodies is inspiring. There is a pleasant interaction
between the orange flash on the clay surface caused by the woodfiring
technique and the subtle blue/grey of the protoceladon/ guan-like glaze
surface. Some of these pots are so translucent that you cannot only see
through them, but you can even see the colour of the flashing through
I have consciously avoided firing these bowls on the rims to keep them
flat and symmetrical, rather, I have allowed and even encouraged some
warping, which I believe expresses some of the simple natural beauty of
this ancient technique. I also work on a slowly revolving treadle-style
kick wheel. This method of throwing also has its own natural character.
There is something about the slow rhythmic pulse of the kick wheel that
can cause the thin wet rim of a finely thrown porcelain bowl to result
in a slight eccentricity, which I find engaging. Not bent or slumped,
just slightly out of whack. Likewise, I have avoided using ribs or profiles
in throwing. I decided long ago that I preferred the hint of soft undulations
left by my fingers on the surface.
I also lift all of the pots off the wheel head with my fingers, I don’t
use batts, this also adds its extra touch of character and in firing I
avoid the use of porcelain setters to encourage a gentle movement in the
foot and consequentially the rim. Some pieces do not survive this combination
of trials looking their best. However, others survive looking ‘natural’.
Of course they are not natural, far from it. These pots are contrived
but they look like they have that something that we have lost in our postmodern,
post-industrial society. They show a direct link to the place and methods
of their making. I believe that all this gives the work a greater authenticity.
It certainly is rewarding for me as the maker and after all, I am making
them for me.
Fifty years ago the well known Australian potter, Ivan McMeekin, discovered
a weathered igneous dyke associated with a coal mine in Mittagong, from
which he was able to coax a similar porcelain body. Interestingly although
these bai-tunze materials are not associated with that geological event,
which is no longer accessible since a freeway was built through the site,
there are, however, other clays and rocks in the area that are now shown
to have the same or even greater potential. The Southern Highlands turns
out to be an interesting geological area in that it has produced similarly
useful porcelain, and proto-porcelain materials.
Founding members of the Potters Society, Ivan McMeekin, Ivan England
and Peter Rushforth were keen users of local materials, not always because
of their special qualities, but rather because there was no reliable supply
of Australian materials such as felspar at that time. McMeekin’s
students Col Levy, Gwyn John (Hanssen-Pigott) and Les Blakeborough have
also developed bodies and glazes from local sources. However, to the best
of my knowledge pots like these have not been produced in this area for
50 years, not since McMeekin’s time at Sturt Workshops.
materials have been here a long time, and I have lived and worked here
for close to 30 years. It has taken me almost that long to track down
and discover all of these materials. I’ve come to realise that it’s
not just the place, it’s the head space. It is only now that it
has all started to come together for me, the slow combination of me homogenising
with country, like making a frit, these things take time to fully integrate.
I have systematically searched the entire shire, collecting hundreds of
materials and making thousands of tests from them. So far I have filled
many notebooks and made many individual batches of porcelains, from four
bai-tunze-like materials, two primary kaolins and several igneous rocks
such as basalt, syenite and granite.
Bai-tunze No1 is a weathered felspathic material. This weathering has
resulted in a small amount of clay mineral being present in the rock,
such that after milling it develops poor plasticity. However the large
amount of felspar that remains unweathered develops a remarkable translucency.
The remainder of the material is quartz which helps develop the glaze
When I first collected this rock I thought that it might be a useful
candidate as a glaze ingredient. However it looked so unpromising that
it sat on my bench for a year until I finally began testing it. Being
a hard rock and finely crystalline, I thought that it might be a sandstone
or a quartzite. It required primary crushing in a jaw crusher and then
several hours of ball-milling to achieve the desired degree of fineness
for testing. The 100 per cent position on the glaze test tile revealed
a vitreous grey surface with a slight sheen. Initial testing as a glaze
ingredient involved line blending with calcium carbonate and silica, both
individually and together in various percentages. Line blending with calcium
carbonate, between five and 25 per cent, turned the rock into a range
of useful glazes, 15 per cent resulted in a guan-like glaze. I was quite
surprised at this result, but pleased, as I thought that it might just
turn out to be just another sandstone sample. The only negative result
was the crawling of this viscous glaze, a result that I am not unfamiliar
with in this type of glaze, However, crawling is most usually associated
with plastic materials, and this was obviously hard rock and not at all
plastic – or so I thought. Reflecting on the crawling I decided
that it might be possible that the rock could have some plastic quality.
I took a small handful of the fine milled powder and mixed it with a small
amount of water in the palm of my hand, and unbelievably it became marginally
plastic, sufficient to allow a poor coil and push-pull test to be made.
I have to admit that I was so surprised that it took me a little time
to gather my thoughts, but not too long. I soon had a set of shrinkage
bars and translucency wedges made and drying. The fired results of this
indicated a grey, vitreous shiny clay body with translucency up to 5.4
mm thick in reduction and perfect glaze fit with a standard limestone
glaze. I thought about this Australian bai-tunze-like material, trying
to understand its nature. Examination with a hand lens showed a fine crystal
structure with opaque crystals that I guessed to be felspar, some obvious
shiny quartz fragments and only a few fine black dots that I assumed to
be biotite mica.
also compared samples of the broken rock with clean geological samples
of felspar in the lump form and compared cleavage planes and fracture
angles. Some of these angles fitted together like a jigsaw puzzle, this
comparison led me to believe that my bai-tunze was primarily a highly
felspathic rock. The fact that there was little or no flashing on the
exposed clay body sample in the wood firings led me to believe that the
felspar was one of the plagioclase series, with a small calcium content,
probably at the albite end of the series. The calcium content must be
small, as there is only a slight tendency for the pots to squat during
the stoneware firings in the wood kiln to between cone 8 and 9. However,
firing to cone 10 and above caused squatting.
This theory however turned out to be wrong. Analysis proved the felspar
to be sanidine, a disordered potash felspar. There seems to be enough
mullite and secondary mullite to hold it up at high temperatures, with
the calcium content low enough to increase the translucency without weakening
the secondary mullite structure created by the felspar. This Australian
bai-tunze although quite translucent fires distinctly grey/white in reduction
so I assumed that there was some iron content, although it must be small.
Finding a material like this has convinced me that porcelain isn’t
as remarkable a material as I formerly thought. It seems that there are
several places around the world where this kind of geology and weathering
has occurred and that all that is required is inquisitiveness and ingenuity
and translucent porcelain is the inevitable result. When I started this
research, I assumed that I would end up making brown clay bodies and tenmoku
glazes. So I was pleasantly surprised to find such a range of eminently
usable pale/low iron materials.
I have since paid to have this material analysed with X ray fluorescence
XRF providing chemical analysis as per cent oxide. This revealed high
silica content 76.49 per cent and moderate alumina content 12.93 per cent,
nothing exceptional there. The iron content is negligible 0.56 per cent
and titanium virtually non existent at 0.13 per cent with sodium and potassium
as expected for a weathered felspar 6.53 per cent total. However, the
calcium and magnesium percentage was a surprise and lower than I expected
at 0.27 per cent in total. This was not enough of the alkali earth fluxes
to explain the grey white quality of the fired surface and the lack of
flashing. Subsequent firings have shown that this clay/rock does flash
in the woodfiring, albeit faintly. It shows a soft pale orange/pink flash
around the foot but it is subtle and only reveals itself under close examination
in good light. I am assuming that the pale nature of this flash is due
to the low iron content. It’s interesting just what can be interpreted
from simple physical testing and observation, but it is nice to have chemical
analysis as confirmation.
No 2 is a weathered igneous rock that has intruded through the local sandstone.
This weathering has resulted in a large amount of clay mineral being present.
The original rock has completely disintegrated such that it has become
a grainy, slightly sticky, fine sand-like material. It doesn’t need
to be crushed, as it slakes easily, but needs milling to develop its plasticity.
It appeared that it had lost its flux content during weathering and had
become primarily a kaolinitic material, it didn’t fully vitrify
at the 100 per cent sample, it crazed heavily with a standard limestone
glaze indicating high alumina and lower silica. Because it isn’t
white, it obviously has an iron content. The net result was a material
that flashed well in woodfiring, high in alumina, low in silica and with
When I first collected this rotten rock, I thought that it might be a
useful candidate as a glaze ingredient. It took limestone and silica to
make it into a celadon glaze. It became obvious that it was a useful candidate
as a bai-tunze – one that could be blended together with my other
collected and processed minerals to produce a range of porcelain clay
bodies. The bodies that I developed with a high content of No 2 bai-tunze
have a tendency to craze but develop a splendid red/orange woodfired surface
flash with marginal translucency.
Analysis results showed kaolinite, illite, montmorillonite and quartz,
an iron oxide content of 1.8 per cent, titanium low at 0.13 per cent,
alkalis at 5 per cent and calcium oxide also low at 0.03 per cent. Hence
the good flame response.
The examples above follow the Chinese archetype of porcelain development.
I have also produced two series of porcelains based on mixtures of primary
kaolin, felspar and silica. These on the other hand follow the European
path of porcelain body development.
Kaolin No1 unusually turned out to be extremely pure. It was short with
the only obvious impurity being a slight vein of yellow ochre staining
passing through it. When this clay was blended with felspar and silica
extracted by flotation from a pegmatite dyke material, it proved to be
able to be developed into an extremely white and translucent porcelain
body showing translucency up to 6.6 mm thick in reduction and 7.5 mm thick
in oxidation. Plasticity was virtually non-existent, but this was overcome
by the addition of bentonite. To this end I tested 13 different bentonites,
natural and synthetic, Australian and imported. The Queensland material
‘Turbobond’, proved to be as useful as any and economical
with it, as was the Western Australian product, ‘Bentonite A’.
I think that I have been able to determine the provenance of this sandstone
lens kaolin. It appears to be a weathered igneous dyke. primarily because
of the signs of metamorphism in the surrounding country rock and must
have undergone subsequent leaching and weathering. Analysis revealed 47
per cent silica, 37 per cent alumina, 0.5 per cent iron, and all other
traces as less than 0.0X per cent or below detectable levels2. This is
the whitest and most translucent of the bodies that I have been able to
develop, albeit, the most difficult to throw. Another porcelain paste
that I have been able to create is based on a weathered igneous dyke.
It was developed along the lines of the previous example, that experience
informed my judgement and sped up the development process. I found that
this clay was a primary kaolin weathered from an igneous intrusion, this
was inferred from the remnant effects of upward thrusting on sandstone
on either side of the intrusion. This site was contaminated with irony
shale bands and lignite and other organics.
A series of bodies were prepared along the lines of those previously
The best of these yielded a porcelain showing translucency up to 4.9
mm thick in oxidation and 4.2 mm thick in reduction. Although this series
of bodies was not as pure and translucent as the others, I persisted with
it because it was quite plastic and enjoyable to throw. Analysis revealed
that it consisted of kaolinite, dickite (a closely related clay mineral
to kaolinite), nontronite, (a smectite, similar to bentonite, where iron
replaces alumina in the crystal lattice), the remainder being quartz.
The material showed 51 per cent silica, 32.3 per cent alumina, iron at
1.37 per cent with titanium at 1.19 per cent. Soda was below detectable
levels and the potash was 0.83 per cent with calcium at 0.03 and magnesium
at 0.33 per cent. Although the titanium and iron were both above 1 per
cent, it was still possible to develop workable translucency, although
less translucent than the other bodies. Possibly putting the lie to the
‘titanium eliminates translucency’ theory.
The above combination of clay minerals resulted in a quite plastic clay
body which was capable of bonding large quantities of non-plastic felspar
and silica and still remain throwable. Its strength at high temperatures
due to its high kaolinite content allowed me to introduce several per
cent of calcium carbonate as a secondary flux without sustaining noticeable
slumping. The effect of the addition of calcium carbonate bleaches any
iron oxide present, increasing whiteness and increases the quantity of
body glass developed, increasing translucency. As long as a critical level
is not passed, the porcelain will still hold its form at stoneware temperatures.
The processing of these rocks and clays involves a series of steps depending
on the nature of the material as it is found in the field. Bai-tun-ze
1 is a hard rock which is minutely crystalline and does not respond to
calcining. Calcining is not an option for batches that are destined for
use as a body ingredient. This rock requires a jaw crusher to break it
down to a workable size for further milling.
I have found that it is beneficial to mill these materials in several
small batches over different time periods to gain a material of several
different particle sizes. The resulting bodies are more workable if they
contain particles of several different size gradings. The greater percentage
of the bodies are milled finely with smaller additions of coarser material
that has been milled for a shorter time. This results in a clay that is
better structured and stands up better on the potter’s wheel.
All the firing was done in an extended throat Bourry box kiln. All the
wood was sourced form my property and that of a neighbour. The kiln was
built from homemade fire bricks produced from a local deposit of white
to off/white bauxite. The bricks were handmade in a slop mould and pre-fired
before construction. The basic clay is quite iron stained and few of the
resulting bricks are white, more consistently orange and brown. I made
them as insulating refractories by incorporating various amounts of used
coffee grounds obtained from the local café. These were collected
and sun dried before mixing with the hammer-milled bauxite. As this was
intended to be a fully local project I felt the need to incorporate the
flourishing contemporary café culture/coffee culture that is so
all pervasive in modern first world life and culture. My thesis and the
work devolved from it is so quaint and old fashioned that this is one
of my few concessions to contemporary life.
The results that I have been able to achieve are far better than I could
have let myself believe were possible. When I first started out on this
project, I didn’t even know of the existence of most of these raw
materials. Nor did anyone else. It was common belief in the district among
potters that there was no local source of white felspar or granite. But
it was there just waiting to be discovered, and what materials they are
to work with.
Steve Harrison is a ceramic artist from the Southern Highlands, NSW,