Gene Arnold on thu 3 apr 08
Can anyone out there tell me what I can do to this glaze to change the =
expansion with out changing the look of the glaze or at least not such a =
drastic change??=20
I applied it to the inside of some bowls with Hanna's fake ash on the =
outside. There seems to be a lot of stress on the glaze. In fact one of =
the larger bowls split from the rim to the foot about a 1/2 day after =
coming out of the kiln. Some of the baskets I glazed with the Turners =
beauty pinged a little for a few days. I waited until the kiln had =
cooled to 150 degrees before unloading because the glaze would ping a =
lot when I tried to open it any hotter. I looked at the glaze under a =
magnifying glass and didn't see any crazing, it just seems the glaze =
doesn't quite fit my clay body. The clay I use is Standard 119.=20
Here is the recipe as I used It.
Turner's Beauty cone 10-R
custer 32 ( I didn't have G-200 )
spodumene 21.3
Whiting 2.1
epk 21.3
dolomite 23.4
tin ox. 6.4
Thanks for any help!!!
Gene=20
mudduck@mudduckpottery.net
www.mudduckpottery.net
John Post on thu 3 apr 08
One of the best tools for this is to use a Currie grid. By changing
the amount of alumina and silica in a glaze the expansion changes.
All the fluxes in the glaze will still be the same. The Currie grid
will point you in the right direction, as opposed to taking a shot in
the dark by adding a bit of this or that. If you haven't ever done a
grid, Ian Currie's book Revealing Glazes is a great place to start. I
made my first Currie grids after just reading his books. I attended
one of his workshops a while later.
John Post
Sterling Heights, Michigan
http://www.johnpost.us :: cone 6 glaze website ::
http://www.wemakeart.org :: elementary art website ::
On Apr 3, 2008, at 5:58 PM, Gene Arnold wrote:
> Can anyone out there tell me what I can do to this glaze to change
> the expansion with out changing the look of the glaze or at least
> not such a drastic change??
Steve Slatin on sat 5 apr 08
Gene -- if it's well vitrified with your firing, the easiest
approach would be to add *small* amounts of silica.
The glaze is low in silica, and so if it'll melt right, it
resolves the shortage and reduces crazing in one
step (I am presuming that the fit issue is crazing --
on matte glazes, crazing is often invisible, but the
pinging during cooling is, AFAIK, associated with
crazing rather than being a symptom of too 'big'
a glaze. I've onyl had one shivering glaze, so I
can't speak to this with any authority.)
There is condition when excess silica can actually
accentuate crazing, but that's when there's too
much silica for all of it to be accommodated within
the glass structure. Bailey's "Glazes Cone 6"
has an excellent description of this, with pictures.
I'd suggest a small batch test, maybe 100 g,
dip a tile, add a half gram of silica, second tile,
etc. up to maybe 3 percent. If it doesn't show
results going that far, it probably is a problem
that's not succeptible to a silica approach.
It is possible that the issue with the bowls
is the different glaze on the outside -- radically
different expansions in 2 different glazes,
one inside, one out ... it's easy to see how
the stress could rupture a bowl.
Best wishes -- Steve Slatin
Gene Arnold wrote:
Can anyone out there tell me what I can do to this glaze to change the expansion with out changing the look of the glaze or at least not such a drastic change??
I applied it to the inside of some bowls with Hanna's fake ash on the outside. There seems to be a lot of stress on the glaze. In fact one of the larger bowls split from the rim to the foot about a 1/2 day after coming out of the kiln. Some of the baskets I glazed with the Turners beauty pinged a little for a few days. I waited until the kiln had cooled to 150 degrees before unloading because the glaze would ping a lot when I tried to open it any hotter. I looked at the glaze under a magnifying glass and didn't see any crazing, it just seems the glaze doesn't quite fit my clay body. The clay I use is Standard 119.
Here is the recipe as I used It.
Turner's Beauty cone 10-R
custer 32 ( I didn't have G-200 )
spodumene 21.3
Whiting 2.1
epk 21.3
dolomite 23.4
tin ox. 6.4
Thanks for any help!!!
Gene
mudduck@mudduckpottery.net
www.mudduckpottery.net
______________________________________________________________________________
Clayart members may send postings to: clayart@lsv.ceramics.org
You may look at the archives for the list, post messages, change your
subscription settings or unsubscribe/leave the list here: http://www.acers.org/cic/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com
---------------------------------
You rock. That's why Blockbuster's offering you one month of Blockbuster Total Access, No Cost.
Ron Roy on wed 9 apr 08
Hi Gene,
Looks like - from calculating the expansion that it's crazing - the
following glaze should look the same and not craze. I recommend doing a
1000 gram test batch. If it needs any adjusting let me know.
I don't keep copies of other peoples glazes so send this all back if it
needs more work.
The crazing does not explain the bowl cracking however - was the crack open
or closed after it happened?
The other possibility is cristobalite forming in that clay body - if you
send me some fired I can run a dilatometer test - if you want me to do that
I'll send instructions about how to make the bar I need - it's easy.
Turner's Beauty cone 10-R ....RR revision to lower expansion -
don't forget to add the 6.4 tin.
-----------------
CUSTER SPAR......... 20.00
SPOD........... 29.50
WHITING............. 2.00
EPK................. 21.50
DOLOMITE............ 24.00
SILICA.............. 3.00
----------
100.00
FORMULA & ANALYSIS
------------------
*CaO........ .40
MnO2....... .00
*Li2O....... .19
*MgO........ .32
*K2O........ .06
*Na2O....... .03
Fe2O3...... .00
TIO2....... .00
AL2O3...... .49
SiO2....... 1.97
P2O5....... .00
RATIO 4.02 was 4.06
EXPAN 411.82 was 473.29 (fairly normal)
WEIGHT 217.51
By the way - this glaze is short of silica so it will not be durable when
in contact with acidic food - and a clay matt as well - not the best type
of liner glaze? What does it sould like when you drag a spoon across it?
Does it mark when you do that?
RR
>Can anyone out there tell me what I can do to this glaze to change the
>expansion with out changing the look of the glaze or at least not such a
>drastic change??
>
>I applied it to the inside of some bowls with Hanna's fake ash on the
>outside. There seems to be a lot of stress on the glaze. In fact one of
>the larger bowls split from the rim to the foot about a 1/2 day after
>coming out of the kiln. Some of the baskets I glazed with the Turners
>beauty pinged a little for a few days. I waited until the kiln had cooled
>to 150 degrees before unloading because the glaze would ping a lot when I
>tried to open it any hotter. I looked at the glaze under a magnifying
>glass and didn't see any crazing, it just seems the glaze doesn't quite
>fit my clay body. The clay I use is Standard 119.
>
>Here is the recipe as I used It.
>
>Turner's Beauty cone 10-R
>
>custer 32 ( I didn't have G-200 )
>spodumene 21.3
>Whiting 2.1
>epk 21.3
>dolomite 23.4
>
>tin ox. 6.4
>
>Thanks for any help!!!
>
>Gene
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
| |
|
