ranmcc@MSN.COM on sun 9 aug 09
Are there any issues with clay and glazes that vitrify at the same cone?
I noticed that a cone 10 clay I used with a cone 6 glaze did not pin hole
where a glaze and clay that matured both at cone 6 did have pin holes??????
Randy
Cotton Patch Pottery
members.tripod.com/~McCallJ/index.html
or
if you like birddogs
members.tripod.com/~McCallJ/MCCALL.html
William & Susan Schran User on sun 9 aug 09
On 8/9/09 7:50 AM, "ranmcc@MSN.COM" wrote:
> Are there any issues with clay and glazes that vitrify at the same cone?
> I noticed that a cone 10 clay I used with a cone 6 glaze did not pin hole
> where a glaze and clay that matured both at cone 6 did have pin holes????=
??
Randy,
I think the goal for functional ware would be to have clay & glaze mature a=
t
the same cone.
That the glaze didn't pinhole on the ^10 clay would lead me to suspect the
^6 clay you are using May require a longer or higher temperature bisque
firing.
Do all of your glazes pinhole on the ^6 clay you are using?
If it is only one glaze, then that glaze may need to be adjusted by subbing
materials that don't outgas as much or the glaze firing may need a soak at
the end.
Too many variables and not sufficient information about clays/glazes/firing=
s
you are using to determine a single reason for the pinholing.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Ron Roy on tue 18 aug 09
Could also be an unclean bisque firing - too low or not enough oxygen to
help burn out the impurities - it would help to know what kind of clay and
how the kiln is fired for both bisque and glaze.
All glazes go through a boiling stage - it could also be the cone 6 body
helping to melt the glaze more - having the recipe for the glaze would help
find that out.
RR
On Mon, Aug 10, 2009 at 11:54 AM, Snail Scott wr=
ote:
> On Aug 9, 2009, at 6:50 AM, ranmcc@MSN.COM wrote:
>
> Are there any issues with clay and glazes that vitrify at the same
>> cone?
>> I noticed that a cone 10 clay I used with a cone 6 glaze did not pin
>> hole
>> where a glaze and clay that matured both at cone 6 did have pin holes?
>>
>
>
> Pinholes are caused by outgassing, so
> evidently your ^6 body was losing some
> volatile materials near ^6, while your
> ^10 clay was not. It's still better to use a
> clay that matches your glaze maturity
> temperature, since an underfired body can
> lead to crazing in the glaze later on, as the
> clay absorbs moisture from dishwashing
> and from the atmosphere. A properly
> matured body will also be stronger and
> less likely to chip or break during use.
> Also, underfired clay which absorbs
> oils through the crazing or the dry foot
> can come to smell stunningly rancid!
>
> Pinholes can often be cured by a longer
> soak, allowing the gasses to escape
> completely, then allowing the glaze to
> melt back smoothly over the holes. Don't
> let the temperature rise, just hold it steady
> or very slowly cool.
>
> -Snail
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
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