Janet Kaiser on tue 1 oct 02
It is interesting to hear what different people understand by "stoneware".
It is, of course, a very imprecise term. There is "stoneware", the
adjective to describe the end product/pot and "stoneware" meaning a
plastic, refractory clay. I have a feeling that we are confusing the terms
and that they mean different things to different potters and clay
producers.
In 1955, there was an attempt to agree on an "International Nomenclature"
of terms and meanings. Known as the "Brussels Nomenclature", it included a
section on ceramics and listed China clay, earthenware, stoneware, etc. It
is/was mainly applicable to industry, but because most potters buy clay
which is manufactured, this protocol should really still apply.
Or has there been a change since? I know the medical profession has spent
years trying to find expressions and words which are truly international
and not eurocentric. So "Achilles tendon", for example, is now just a
footnote of medical history (ouch!).
In my college notes (1970s) according to the Brussels Nomenclature,
stoneware was: "Dense, impermeable and hard enough to resist scratching
with a steel point". It was also "More opaque and normally only partly
vitrified (in comparison to porcelain)".
Now I know for certain that some clay sold as stoneware and fired to high,
stoneware temperatures would certainly scratch with a steel point. And they
would also let moisture through the fired body. Does this mean it is not
really true stoneware?
After all the very word implies clay which has "turned to stone". Yes, some
stone is porous, but the idea of hardness and impermeability applies to
most.
I personally would deem a pot "real stoneware" if fired to at least 1200
=B0C, usually 1260-1300 =B0C but often up to 1340-50 =B0C; to be only 2%-3%
(5% max.) porous; not high in iron (i.e. not red in colour); and have an
unmistakable glassy surface. This is in addition to the hardness factor
whether "measured" with the steel point or not and totally "waterproof".
Then there are the more subjective hurdles to win the JFK Seal of Stoneware
Approval... The glaze. Hummm... That certain something that all high-fired
stoneware has and other lower-fired glazes just do not. At least the ones I
have seen to date have not, so don't all shout at me! All the cone 6 I have
seen in the buff, are perfectly reasonable glazes, but not up to "true
stoneware" IMHO. They are going to be real wood ash or feldspar-based
glazes.
Because there have been no really satisfactory substitutes for lead glazes
for earthenware, I personally believe we have actually moved away from
having earthenware and stoneware, so we now have a "super earthenware"
which is being marketed as "stoneware". We actually lack a word for these
new clays... I notice that people talk a lot about cone 5 and cone 6, which
in truth is what I perceive as the "super earthenware" category.
Am I alone in thinking we really need a new category, or am I splitting
hairs? Does "low fired" and "high fired" stoneware suffice? I just know
that each potter has a different definition of what they consider to be
stoneware. Ye gods! I even know one who thinks Raku clay fired to 1200 =B0C
is then "fully vitrified stoneware"!!! It would scratch with a pin and
practically crumbles apart as soon as you look at it. As for the tongue
test... OUCH! But they stick to their guns!
Sincerely
Janet Kaiser
The Chapel of Art =95 Capel Celfyddyd
8 Marine Crescent, Criccieth LL52 0EA, Wales, UK
Tel: 01766-523570 URL: http://www.the-coa.org.uk
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