Techno Tip

Dealing with discontinued clay materials

Allofus mixing ourewn clay bodies could
stand knowing a lithe more about the ma-
terials that make them up, We tend to just
use them without thinking abet (he prog
erties they impart (when I say ‘we’ I am
also referring to clay body manufactur-
ers}. Then when a material is no longer
available we panic, look for a substitute
that some people claim to have, try it and
then act surprised when it does not work
the same. Finally we buckle down and
study the lost matenal and armed with
better questions we have another go at
dealing with the situation. The demise of
Newman Red clay is an instance of this
situation. As of May 2003, it is no longer
available. Prior to that time the supplier,
Gladding, McBean & Co., was having
problems with consistency of the product.

Newman is a red burning low plasticity,
low dry strength fireclay usctul in both
plastic and casting bodies to impart red
colour. It has powerful staring abilities
fheyond what its percentage of iron sug-
pests). Forexample, even if dilutedto 50%
in arecipe the body can stall fire bngit red
in oxidation. Newman clay has a very fine
particle size Coupled with some large im-
purity particles in the plus 50 and even
plus 30 mesh range. The crude matenal
colour is bright orange. Not surprisingly,
bodies containing it complement it with
hall clay and feldspar.

Coming up with an economical substitute
for this maternal is a tricky task both be-
cause of its unusual properties and unique
combination. For example, there is mo
other commonly available smooth refrac-
tory red burning clay material in North
America. Thus some have suggested sub-
atituting various low and mid-fire red clays
to impart colour to clay bodies (i-e.
Carbondale Red. Redart). However this 15
not practical since these materials flux the
body producing a more vitreous and
browner fired result. Even if feldspar is
removed from the body to compensate, the
ted colouration is still compromised to
brown. Some have suggested mixes of
fireclays mined in the same area (ie. MICO
400, 800, Lincoln Fireclay). However these
are mot nearly refractory enough erther
{and therefore not fireclays) and they have

September 2003

by Tony Hansen

far less iron. Other refractory red clays are
not fine grained like Newman and contain
iron speckle orather impurities (c.g. Plains-
man Pirered). Also, Newman has a high
firing shrinkage: substimmtes will likely be
lower (this is not a bad thing of course
unless continuity of fired dimensions arc

Imypeartinn },

Understandably any substitution strategy
is going to have to involve a mix of mate-
rials, inchading iron oxide (even though it
is messy and more costly), [Lis also going
toinvolve understanding yvanous tradeoffs.
I have compounded a series of mixes to
replace Newman (both from physical prop-
ertics and chemistry perspectives) and have
compared their merits by inserting them in
Place of Newman in a body recipe calling
for 30%. I have evaluated colour, absorp-
tion and fired shrinkage over a range of
temperatures, drying shrinkage and dry-
ing performance, particle size distibu-
tion, e6c. So far one mix of materials has
proven quite similar to the character of the
colour, the maturity, the smoothness and
the nature of the plasticity. [ am mot yet
sure if the thermal expansion is the same
simce I have not used any glaze yet.

[f you would like to know more about this,
please visit www cerumicmaterials.info
and search for Newman. You will find
complete informalion onils properties and
links to various materials that are similar.
At this website | am attempting to create a
matenal-centric brary of ceramic infor-
mation that is publicly available and talks
directly to my Digitalfire INSIGHT soft-
ware. It is already quite large and we have
jots of interest from around the world from
potential authors of material, toxicity, ax-
ide, and related information. For an over-
view, click the About link on the home
page.

Tory Hansen Digitalfire Corp.

Platnsran Clove Led. in Medicine Hat, Alberta
Har, ane ter lace! afiliares, Greeibyirn Pouters
Sapply td. in Sorrey, and Farcomeer Urlend
Patiers Supply on the deland generously spor:
sor fhe Techno Tip colwnn

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