Erin Hayes on wed 2 jul 97
Hello all!
I have lately been using a clay body from Seattle Pottery Supply, called
"Vashon Brown." I like it very much because of its rich chocolatey
color, but I am a little nervous about the colorant that may be creating
the brown.
I have asked at the Pottery Supply a little, but no one has yet been
very forthcoming about the colorant. I haven't pressed the matter, but
I would at least like to know the possibilities so I can either press
harder or stop worrying.
My question is, what colorants could be used in a Cone 6 body to create
a rich brown? Only once have I found a tiny piece of what looked like
raw colorant - and it looked very much like manganese. If this is what
produces the color, I think I may need to change clays.
Tom Buck, Karl Platt and other techno-clay gods - can you offer any
ideas?
Please reply directly - Thanks!
Erin.
Tom Buck on fri 4 jul 97
Erin: Most likely, the colourant in your C6 claybody is iron,
as iron oxide red (Fe2O3) or possibly as iron oxide black (FeO).
And this iron will probably come from a natural clay high in iron
blended with other materials to yield the claybody you use. Bodies
with significant amounts of iron compounds show darker colours
as the firing temperature is raised. At C06 the colour may be
pale pink but by C8 it has become dark brown.
Examine these factors please. One, what is the colour of
your bisqueware? I'd guess salmon coloured, pink or sockeye.
Two, does any substantial specking occur? I suspect not. Three,
does the cost of the claybody fall within expected range of
midfire stoneware claybodies? Or is it more expensive by a
substantial (10-20%) margin? (Most mineral oxide colourants cost at
least 3-5 times as much as a coloured clay).
To make a midfire claybody, most formulators choose a
blend of natural (ie, low-processed) clays rather than use
materials that are are closer to a commerical "chemical/mineral".
A good throwing body often contains much more than 50% clay from
a combination of the following:
a stoneware clay (eg, Redstone), a ballclay (eg, Old Mine
#4), a fireclay (eg, Hawthorne Bond or Goldart),
an earthenware clay (eg, Redart), and a kaolin (Edgar's
Plastic Kaolin is most common).
To these would be added a feldspar, some flint (silica), and perhaps
some talc, wollastonite, and rarely, some whiting or dolomite. Plus
grog (if specified) and water.
If you fear you are using a body with say 2%+ manganese dioxide in
it, I'd say you can put that fear to rest since you describe the fired
colour as "chocolate" coloured. MnO2 alone gives a distinctive grey cast
to the brown it produces, and besides specking would be noticeable since
commercial MnO2 tends to be on the coarse side (100 m or bigger).
For a more detailed discussion of clay colourants, please see
Daniel Rhodes's Clay & Glazes for the Potter. He discusses claybody
formulation better than most other texts I've read.
BTW, body suppliers have a phobia about giving out any hint of
what components are in a particluar body. So your supplier is doing the
standard thing by keeping silent.
Tom Buck (new email address: )
old:
Hamilton, Ontario, Canada
On Wed, 2 Jul 1997, Erin Hayes wrote:
> ----------------------------Original message----------------------------
> Hello all!
>
> I have lately been using a clay body from Seattle Pottery Supply, called
> "Vashon Brown." I like it very much because of its rich chocolatey
> color, but I am a little nervous about the colorant that may be creating
> the brown.
>
> I have asked at the Pottery Supply a little, but no one has yet been
> very forthcoming about the colorant. I haven't pressed the matter, but
> I would at least like to know the possibilities so I can either press
> harder or stop worrying.
>
> My question is, what colorants could be used in a Cone 6 body to create
> a rich brown? Only once have I found a tiny piece of what looked like
> raw colorant - and it looked very much like manganese. If this is what
> produces the color, I think I may need to change clays.
>
> Tom Buck, Karl Platt and other techno-clay gods - can you offer any
> ideas?
>
> Please reply directly - Thanks!
>
> Erin.
>
Darrol Shillingburg on sun 6 jul 97
Hi all,
I have used a "dark brown" clay body from Laguna called B3Brown. Cone 5 and
colored with Manganese dioxide, amongst other things. The MSDS provided by
the manufacture states clearly the manganese content, ( 5%) although going
lightly on the manganese hazards.
Ask your supplier for a Material Safety Data Sheet on the clay. If there
are hazardous materials in the clay formula the manufacturer must tell you.
----------
>On Friday, July 04, 1997 9:04 PM Tom wrote:
>
> ----------------------------Original message----------------------------
> Erin: Most likely, the colourant in your C6 claybody is iron,
> as iron oxide red (Fe2O3) or possibly as iron oxide black (FeO).
> And this iron will probably come from a natural clay high in iron
> blended with other materials to yield the claybody you use. Bodies
> with significant amounts of iron compounds show darker colours
> as the firing temperature is raised. At C06 the colour may be
> pale pink but by C8 it has become dark brown.
> Examine these factors please. One, what is the colour of
> your bisqueware? I'd guess salmon coloured, pink or sockeye.
> Two, does any substantial specking occur? I suspect not. Three,
> does the cost of the claybody fall within expected range of
> midfire stoneware claybodies? Or is it more expensive by a
> substantial (10-20%) margin? (Most mineral oxide colourants cost at
> least 3-5 times as much as a coloured clay).
> To make a midfire claybody, most formulators choose a
> blend of natural (ie, low-processed) clays rather than use
> materials that are are closer to a commerical "chemical/mineral".
> A good throwing body often contains much more than 50% clay from
> a combination of the following:
> a stoneware clay (eg, Redstone), a ballclay (eg, Old Mine
> #4), a fireclay (eg, Hawthorne Bond or Goldart),
> an earthenware clay (eg, Redart), and a kaolin (Edgar's
> Plastic Kaolin is most common).
> To these would be added a feldspar, some flint (silica), and perhaps
> some talc, wollastonite, and rarely, some whiting or dolomite. Plus
> grog (if specified) and water.
> If you fear you are using a body with say 2%+ manganese dioxide
in
> it, I'd say you can put that fear to rest since you describe the fired
> colour as "chocolate" coloured. MnO2 alone gives a distinctive grey cast
> to the brown it produces, and besides specking would be noticeable since
> commercial MnO2 tends to be on the coarse side (100 m or bigger).
> For a more detailed discussion of clay colourants, please see
> Daniel Rhodes's Clay & Glazes for the Potter. He discusses claybody
> formulation better than most other texts I've read.
> BTW, body suppliers have a phobia about giving out any hint of
> what components are in a particluar body. So your supplier is doing the
> standard thing by keeping silent.
>
> Tom Buck (new email address: )
> old:
> Hamilton, Ontario, Canada
>
> On Wed, 2 Jul 1997, Erin Hayes wrote:
>
> > ----------------------------Original
message----------------------------
> > Hello all!
> >
> > I have lately been using a clay body from Seattle Pottery Supply,
called
> > "Vashon Brown." I like it very much because of its rich chocolatey
> > color, but I am a little nervous about the colorant that may be
creating
> > the brown.
> >
> > I have asked at the Pottery Supply a little, but no one has yet been
> > very forthcoming about the colorant. I haven't pressed the matter, but
> > I would at least like to know the possibilities so I can either press
> > harder or stop worrying.
> >
> > My question is, what colorants could be used in a Cone 6 body to create
> > a rich brown? Only once have I found a tiny piece of what looked like
> > raw colorant - and it looked very much like manganese. If this is what
> > produces the color, I think I may need to change clays.
> >
> > Tom Buck, Karl Platt and other techno-clay gods - can you offer any
> > ideas?
> >
> > Please reply directly - Thanks!
> >
> > Erin.
> >
| |
|
