The only way to make a great plastic
porcelain body is with Grolleg Kaolin,
right? *Grolieg porcelains’ have achieved
a status that almost dismisses all others, Is
this real or is it politics? Like many paliti-
cal topics, this one looks more interesting
the deeper you go. T would like to outline
some of the misconceptions about Grollez
porcelains that | have discovered.

First of all, information is very sparse
regarding Grolicg. The closest I could
come was the English China Clays website
where | found mention of it. Temailed and
pot back a terse datu sheet with a one
sentence descripsion: “A white firing china
clay used extensively in vitreous table-
ware formulations but also suitable for
high quality carthenware or electrical por-
celan.”

Consider the first misconception: Grolleg
makes great plastic porcelains.

This is falee. It is mot the Grolleg that is
responsible forthe plasticity in the Grolleg
porcelain throwing bodies. It is actually
more of an impediment to plasticity. I did
a side-by-side companson, adding water
to some Grolleg and 6 Tile kaolin. Al-
though the Grolleg slip likes to hang onto
its water in companson, when enough
water is removed to produce a stiff plastic
material, the plasticity of Grolleg pales in
comparison, [t crambles and breaks com-
pared to the plasticene-like 6Tile. This
means that bodies employing Grolleg re-
quire another source of plasticity,

Does that mean using another clean
white kaolin?

Not really because even the most plastic
kaolins at 50-60% of the body will not
produce enough plasticity. That means
you need to adda ‘dirty’ higher iron mate-
rial like ball clay or bentonite. This sky-
rockets the iron and destrovs the whole
purpose of using an expensive white bum-
ing kaolin in the first place. There are bots
of porcelain recipes like this; it is poant-
less.

Hectorite produces plasticity in Grolleg
bodies without compromising whiteness:

This is true, but misleading. Other proper-
ties we compromised using such an ap-
proach (see below). Yes, some hectorites

4

Techno Tip
The Politics of Grolleg Kaolin

wre very white burning, however they cost
about 365 per bag! Is it fair to compare a
cost-is-no-object Grolleg porcelain with a
traditional porcelain and make a blanket
statement that Grollee bodies are better?
Hardly, There are expensive white North
American materials also. In fact, there are
Inexpensive ones also,

Grolleg bodies require less feldspar so you
Can use more and therefore get better plas-
ticity: No, you only need to add 5% feld-
spartod Tile kaolin to get the same amount
of ftux. 5% more non-plastic Grolleg kap-
lin at the expense of feldspar will de little
for body plasticity,

Grolleg is low iron:

False, [t contains up to 0.8% iron. This is
the same as EPK. 6Tile and Sapphire have
less. Yes, side-by-side the Grolleg will fire
alittle whiter in spite of this, however you
must remember that a plasticizer has to be
added to the Grolleg. This destroys the
advantage unless you are willing to pay the
big bucks.

Grolleg porcelains break all the rules: they
are plastic yet dry perfectly, vitreous yet
do mot warp or shrink, white buming amd
yet have the working properties of a stone-
ware, have low drying shrinkage yet good
dry strength:

Let's getreal! A common Grolleg recipe is
G200 Feldspar 20, Grolleg 45, Silica
and Hectorite 5. If you try mixing this up
you will note that although the hectorite
does impart good plasticity, this crow-bar
approach to plasheity produces dned ware
that is very fragile and cracks can develop
easily if ware is not dried evenly. And it
warps and expands just like any other
overtired boxy.

If you are really sharp you will likely be
criticizing me by now about a critical
oversight. Grolleg koalin is very bow in
TiOZ, This oxide has an opacifying effect
on translucent porcelains. Thus very thin
ware using this material has the potential
of being quite translucent. OK, you've pot
me. Howewer | was talking about white-
ness, oot translucency, The subject of trans-
lucency brings up another whole can of
worms,

Potters Guild of British Columbia Newsletter

There are lots of other cost-is-no-ohject
ways to making white porcelains.

You can add zirconium silicate. You can
use an ultra-low iron white buming North
American delaminated kaolin with
hectorite, You can use less of a plastic
kaolin to make more room for other whiter
burning minerals, You can use # Jow iron
plastic kaolin and use alumina rather than
silich. You can even add a small amount of
blue stain to an otherwise slightly yellow-
ish firing porcelain to make it look bright
white. It is amazing how many miscon-
ceptions there are about materials we use,
To me this demonstrates that there is noth-
ing like taking materials into your own
hands and seeing for yourself.

Tony Honsen

Techvio Tp is generously supported by
Plainsman Clive Limited in Medicine Hat,
Alberta and ity affiliates, Greenbom Poners
Shayely in Serer ana! Varncowver Island
Pottery Warehouse in Nanaimo.

Gordon Hutchens
Workshops at Shadbolt Centre

Gordon Hutchens will give two
workshops this summer:

Firing the Ombu: Bring your cone
10, bisqued (glazed or slipped) pots
ro fill 4 cu. fe in our new, wood!
soda firing kiln. Gordon takes you
through the complete process in-
cluding some bisque slip decora-
tion, loading (Wed, July 17), firing
(Thurs & Fri}, unloading and cri-
tique (Mon July 22). Cost is $321.
Hours vary, but course begins
S00AM, July 17.

And. while rhe kiln is cooling ...

Rakw with Gordon: Hands-on ex-
ploration or Raku including demos,
discussion and slides relating to
glazes, glaze application and firing.
Bring 6 average sized (6° diam-
eter}, bisqued pots, Cost: $130.54,
Sat July 20 & Sun July 21,
10:00.4M-4:00PM

Discount for two workshops.

Information or © register
604.291.6864.

May 2002