Kelly Johnston on thu 13 mar 08
I am wondering about the possibilities of the clay I am using at the
moment. It is labelled as Cone 10, but also gives the information that
it only vitrifies at 1350 + Celcius. I am firing in an electric
oxidation atmosphere, and am interested in trying out some cone 6
glazes. What are the ramifications of only firing my cone 10 body to
cone 6? I imagine it will have an effect on the durability of the
pieces, but how big of an effect? I mainly make functional thrown
pieces. I was thinking that if its not vitriried at cone 10, then
taking it down to cone 6 might not be such a big deal. Is it a sensible
thing to do, or should I just plow thru this cone 10 clay and then
purchase something more suited to cone 6? I have alot (for me) of this
clay to get thru, and have learned alot about what questions to ask
before ordering clay in bulk lol!
Thanks for any help!
Kelly in Emerald, Qld Australia
Dolita Dohrman on fri 14 mar 08
Kelly, I started out believing the clay manufacturers when they
showed in their catalogs that range clays (^6 - ^10) were vitrified
at ^6. If I recall correctly, proper vitrification is below 2%.
Since I make functional work, I started testing a number of range
clays. The results were well above 2%. After listening to some of
our more learned members here on the list, I really believe there is
no such thing as a range clay that is vitrified at ^6 (unless, of
course, the end range is ^6). I have spent the better part of two
years searching for a good ^6 clay that will let me hand build, throw
and make tiles. It seems I have settled on Bella's Blend from
Highwater.
If you use a ^6 - ^10 clay for functional work and your glaze
crazes...sometimes invisibly...you will get moisture seepage through
the foot of the piece. Not good. Also, the absorption factor of any
unglazed surfaces (the foot) from putting the piece in the
dishwasher, or just washing in the sink, can change glaze fit way
down the road and cause problems in the microwave. Use your range
clay for non-functional pieces until it is gone and order a good ^6
stoneware for your functional work. I also stock Little Loafers (a
^6 porcelain) and Earthen Red (a ^6 red clay) in my studio as some of
my glazes look better on these claybodies. These two are also from
Highwater.
Dolita
On Mar 13, 2008, at 7:51 PM, Kelly Johnston wrote:
> I am wondering about the possibilities of the clay I am using at the
> moment. It is labelled as Cone 10, but also gives the information that
> it only vitrifies at 1350 + Celcius. I am firing in an electric
> oxidation atmosphere, and am interested in trying out some cone 6
> glazes. What are the ramifications of only firing my cone 10 body to
> cone 6? I imagine it will have an effect on the durability of the
> pieces, but how big of an effect? I mainly make functional thrown
> pieces. I was thinking that if its not vitriried at cone 10, then
> taking it down to cone 6 might not be such a big deal. Is it a
> sensible
> thing to do, or should I just plow thru this cone 10 clay and then
> purchase something more suited to cone 6? I have alot (for me) of this
> clay to get thru, and have learned alot about what questions to ask
> before ordering clay in bulk lol!
>
> Thanks for any help!
>
> Kelly in Emerald, Qld Australia
>
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