Cat Yassin on wed 22 oct 03
I just opened my kiln to disappointment :(=A0=A0 I'm needing some advice or=20
possible confimation of what may have been my problem/s.
I used RR Raspberry on some bowls with swirls of Varieted Blue (sp?). I also=
=20
used Chris Wolf's Plum with swirls of CW Cream (these usually turn out=20
fabulous). I had a hard time getting to Cone 6 on the top shelf. The bottom=20=
shelf=20
went all the way to Cone 6 and I had to slow cool by then and when I opened=20=
the=20
kiln the 7 was down as well (only on the bottom).
I know I didn't have the Raspberry thick enough because I ended up with more=
=20
of a pink. My intial tests were more burgundy or deeper raspberry. But I jus=
t=20
mixed up a bigger batch and didn't do a test and I now know the glaze was=20
thinner than my original test batch. Actually the color isn't the problem. T=
he=20
bowls in the top (Cone 6 was bent to a 2:00) had a few craters but where the=
=20
Varieted (sp?) Blue was there was crawling. The crawling was only where I ha=
d the=20
Raspberry overlapped as my glaze batch was only big enough to dip half a bow=
l=20
at a time so there was a 1/4" to 1/2" overlap line down the middle of the=20
bowl. And again there was only crawling where the Raspberry overlapped and t=
he=20
Varieted Blue was on top. No where else, not even where the Raspberry overla=
pped=20
with no Varieted Blue. However on the outside of the bowl where the Varieted=
=20
Blue was over the Raspberry, no crawling. In hotter parts of the kiln the=20
Raspberry really cratered bigtime.
Ok, on to the Chris Wolf Plum bowls. The top part of the kiln where it didn'=
t=20
get hot enough the plum wasn't very glossy and there were craters. In the=20
hottest part of the kiln the glaze was very glossy as I like it, but lots mo=
re=20
craters. And where the CW Cream was swirled there were more pronounced crate=
rs=20
(possibly pinholes?). And where the pinholes were you could see that the gla=
ze=20
was darker around the pinhole as it had pooled there and didn't smooth out.
I also did about 20 little mini bowls testing new glazes from Mastering Cone=
=20
6 Glazes and some other Cone 6 glazes from other sources. There were=20
CONSISTENTLY craters no matter where they were in the kiln, except for a few=
glazes=20
that overlapped where there was no cratering. Oh... such frustration!!! I wa=
s=20
totally mystified until I saw one little bitty test bowl with Raspberry and=20=
4=20
other glazes on it that was absolutely gorgeous. NO craters whatsoever and t=
he=20
Raspberry was stunning, the gloss was magnificent all around, and the whole=20
little bowl was smoother than a baby's butt. I turned the bowl over and real=
ized=20
it was different than my other test bowls. Aha! The only piece in the whole=20
kiln that had a totally different clay body! A little sushi bowl with an S c=
rack=20
in it that I saved for my glaze testing. Ok... all the bowls with the=20
cratering were made with Cone 5 Cinco Blanco and the one little perfect bowl=
was made=20
I'm sure with Cone 5 Bee Mix. When comparing the two clay bodies on the bott=
om=20
of the glazed pieces where the clay was exposed I noticed that the Bee Mix=20
was much smoother and whiter and the Cinco Blanco more coarse.
Ok, given all the information... is it safe to assume that for the glazes I=20
was testing the Cinco Blanco was the overall problem for the cratering? I do=
=20
think that the CW Plum with the CW Cream on top that blistered bigtime just=20=
got=20
too hot and perhaps the rougher clay exasperated the situation. As for the=20
Raspberry with Varieted Blue on top that crawled only where the Raspberry=20
overlapped... I don't have a clue. I did wipe all the bowls with a damp spon=
ge before=20
glazing to clean out any dust. (On a side note, my first test combining thos=
e=20
two glazes was on a little vase, a vertical piece and no crawling.)
If the clay is my problem, I don't want to say the Cinco Blanco was bad, but=
=20
it just didn't work for me and the glazes I was using. Of course I will do=20
some more tests this week. Thanks in advance for any advice and comments!
-Cat Yassin
John Hesselberth on thu 23 oct 03
On Wednesday, October 22, 2003, at 03:06 PM, Cat Yassin wrote:
> If the clay is my problem, I don't want to say the Cinco Blanco was
> bad, but
> it just didn't work for me and the glazes I was using. Of course I
> will do
> some more tests this week. Thanks in advance for any advice and
> comments!
Hi Cat,
You've had a tough experience. I, and I'm sure most everyone on the
list, send our sympathy. I have read you story carefully and ,
frankly, all I can do is offer some guesses.
Clearly your lead on the clay body difference is the best one you
have--thank goodness you had that one pot of a different body in the
firing. Your Cinco Blanco may need to be bisqued higher to clear it of
all the organics, or it may be outgassing when you overfire it--you
said it was a cone 5 body so it was clearly overfired in bottom of your
kiln which got to ^7.
It is much less likely, however I would also go back and check your
glaze ingredients. What I have in mind is maybe a new batch of one of
them that is used in both glazes--and might have been mislabeled. In
any case, it would be worthwhile to fire your kiln with only a few test
pieces in it next time and see if you can better sort things out. Good
luck.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
Carol Tripp on thu 23 oct 03
A tiny part of what Cat wrote:
>If the clay is my problem, I don't want to say the Cinco Blanco was bad,
>but
>it just didn't work for me and the glazes I was using. Of course I will do
>some more tests this week. Thanks in advance for any advice and comments!
>
Hi Cat,
I use a few glazes that can only be used over grogless clay, Pete Pinnell's
Strontium Matt is one of them. It took me ages to figure this out and lots
of frustration.
Sometimes the answer stares us in the face but we don't see it. Hope you
can solve your problems.
Best regards,
Carol
Dubai, UAE
_________________________________________________________________
Help STOP SPAM with the new MSN 8 and get 2 months FREE*
http://join.msn.com/?page=features/junkmail
Cat Yassin on thu 23 oct 03
In a message dated 10/23/2003 1:21:01 PM Central Daylight Time,
john@FROGPONDPOTTERY.COM writes:
> Clearly your lead on the clay body difference is the best one you
> have--thank goodness you had that one pot of a different body in the
> firing. Your Cinco Blanco may need to be bisqued higher to clear it of
> all the organics, or it may be outgassing when you overfire it--you
> said it was a cone 5 body so it was clearly overfired in bottom of your
> kiln which got to ^7.
>
Thank you John for your advice. I bisque to 04 on all my pieces. I have
however gone and looked at all my pieces in the past year that the glaze had
problems. They are easy to find because they sit on a shelf collecting dust, lol.
After this firing I started thinking, "Hmmmm, this problem looks familiar to one
I've had in the past" so I started checking the bottoms of the pieces with
cratering and voila! they all look to be the Cinco Blanco. I did not find any
that had a clay that looked like the Bee Mix.
Ok, another question: Can I take the Cinco Blanco pieces that are already
bisqued and not glazed and bisque fire them again to say 03? I would like to see
if that will make a difference when I glaze them....
-Cat Yassin
San Antonio, Texas
Cat Yassin on thu 23 oct 03
In a message dated 10/23/2003 2:13:45 PM Central Daylight Time,
cjtripp@HOTMAIL.COM writes:
> Hi Cat,
> I use a few glazes that can only be used over grogless clay, Pete Pinnell's
> Strontium Matt is one of them. It took me ages to figure this out and lots
> of frustration.
> Sometimes the answer stares us in the face but we don't see it. Hope you
> can solve your problems.
> Best regards,
> Carol
THanks Carol! Back to the drawing board I go!
-cat
John Hesselberth on thu 23 oct 03
Sure. That might be equivalent to having bisqued them a single time
to, say, 02 1/2 though. John
On Thursday, October 23, 2003, at 03:13 PM, Cat Yassin wrote:
> Ok, another question: Can I take the Cinco Blanco pieces that are
> already
> bisqued and not glazed and bisque fire them again to say 03? I would
> like to see
> if that will make a difference when I glaze them....
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ron Roy on sat 25 oct 03
Hi Cat,
First - one way to encourage crawling is to fire ware wet - so make sure
it's dry before you start - or dry slowly at first at low temperature.
With crawling - often the problem is the basic nature of the raw glaze -
it's not strong enough during the drying and sintering to hold together. It
is an easy fix most times - subbing in ball clay for kaolin is my usual way
- or just adding 1 or 2% bentonite will toughen the glaze up enough.
Let me know if you want me to convert any of those glazes.
Sometimes it's the water - flocculated glazes need more water to be thin
enough - which leads to higher shrinkage.
Overfired clay will produce blisters - the clay is breaking down and
producing gas - which has to exit through the glaze - if refired it gets
worse because the body is even more overfired because of the 2nd firing.
This is exactly the same problem if the organics are not burned out during
the bisque firing - the clay can overfire because of the contaminants or
because the iron is turned into a flux.
Anyway - let me know if you think I can help.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
