gina mars on wed 20 jan 10
Hi All, I was hoping for some insight into a glazing problem that
developed with a student this week.
My student made about 10 tall thin mugs out of a talc clay body,
181 standard. She lightly brushed them off with a wet sponge and then
dipped one at a time in a cone 6 glaze. Then she dipped the rim about
2 inches down in another color when the piece was dry, approx 15
minutes. The second glaze cracked and peeled off.
now, my thinking is that the piece was too thin to absorb two glazes.
I personally do not throw that thin but have had a similar problem
were I dip a piece in 2 glazes and it literally makes pull away round
spots kind of like oil and vinegar would. It doesn't bother me much
because these are usually somewhat runny glazes and they fill in the
effected area when fired. Also, when firing some cone 10 glazes like
Tom Turners red, I usually dip the red in another color after the red
and that glaze always peels away. Tom said he has that issue but
didn't elaborate on fixing it.
The glazes my student used were checked and did not seem too thick.
She also didn't dip for too long a time period.
A while back i remember someone somewhere giving an explanation for
this glaze issue and a possible correction. Any help would be greatly
appreciated.
At home pugging and getting ready to revamp my website.
Gina Mars
www.marspottery.net
Snail Scott on wed 20 jan 10
On Jan 20, 2010, at 8:12 AM, gina mars wrote:
> ...Then she dipped the rim about
> 2 inches down in another color when the piece was dry, approx 15
> minutes. The second glaze cracked and peeled off...
This seems like the smoking gun to me.
Especially with thin or not-very-absorbent
clay, the moisture of the second dip has to
go somewhere, and the dried first glaze layer
is it. Some glazes are not too expansive, but
many are, and when re-wetted, will expand
and peel off of the clay. A common cure for this
is to re-dip before the first layer is fully dry. The
second glaze may need to be thickened a bit
to achieve a sufficient coating.
In your case, though, you say that only the second
layer peeled, not both? This is less common, but if
this is the case, I would attribute it to a dustiness
in the first glaze, which gives the second glaze
nothing to hold on to. Dipping while moisture still
remains in the first coating can sometimes also
solve this, and adding bentonite or another surface
hardener also can help by reducing dustiness in
the dried glaze layer.
-Snail
David Woof on thu 21 jan 10
Snail=3D2C=3D20
I think the dustiness you speak of is right on=3D2C and while a surface har=
dn=3D
er is key to a solution=3D2C it also indicates that the glaze is likely low=
i=3D
n clay content. If one puts the glaze of higher clay content on first as t=
=3D
he base glaze this problem is usually mitigated or solved. Notice I used "=
=3D
likely" and "usually"=3D2C there are always exceptions=3D2C but this is wha=
t wo=3D
rks for me.
=3D20
Gotta go=3D2C it has been record snowing in the high country and now the wa=
rm=3D
rains are bringing it all down. Rio Verde over the banks at 4:00 am tomorr=
=3D
ow with a projected record flood soon to follow.
Will tie the canoe to the mulberry tree in the court yard tonite and park t=
=3D
he vehicles on higher ground. Love this wild river.
=3D20
David Woof Clarkdale=3D2C AZ =3D20
=3D20
________________________________________________________________________
7a. Re: Glazing problem
Posted by: "Snail Scott" claywork@FLYING-SNAIL.COM=3D20
Date: Wed Jan 20=3D2C 2010 5:11 pm ((PST))
On Jan 20=3D2C 2010=3D2C at 8:12 AM=3D2C gina mars wrote:
> ...Then she dipped the rim about
> 2 inches down in another color when the piece was dry=3D2C approx 15
> minutes. The second glaze cracked and peeled off...
This seems like the smoking gun to me.
Especially with thin or not-very-absorbent
clay=3D2C the moisture of the second dip has to
go somewhere=3D2C and the dried first glaze layer
is it. Some glazes are not too expansive=3D2C but
many are=3D2C and when re-wetted=3D2C will expand
and peel off of the clay. A common cure for this
is to re-dip before the first layer is fully dry. The
second glaze may need to be thickened a bit
to achieve a sufficient coating.
In your case=3D2C though=3D2C you say that only the second
layer peeled=3D2C not both? This is less common=3D2C but if
this is the case=3D2C I would attribute it to a dustiness
in the first glaze=3D2C which gives the second glaze
nothing to hold on to. Dipping while moisture still
remains in the first coating can sometimes also
solve this=3D2C and adding bentonite or another surface
hardener also can help by reducing dustiness in
the dried glaze layer.
=3D20
=3D20
=3D20
_________________________________________________________________
Hotmail: Powerful Free email with security by Microsoft.
http://clk.atdmt.com/GBL/go/196390710/direct/01/=3D
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