Andrew Douglas on thu 1 jun 06
I just want to know whether this is normal or not. I have an explanation
and pictures here:
http://potterboy.blogspot.com/
In summary, I use an ash glaze - 50/50 ash and potash feldspar. Last time
it cracked and left the pot all over the place - in fact, I think it must
have lept off my pots in the kiln as it went everywhere and some times
unexpectedly.
Anyway, this time I added about 10% china clay too, as I'd read this would
help it bond - but now I'm thinking 'bond' here means during firing, as
although it is a little better, the pots are all cracked and flakey.
The glaze also readily went in to a, well, non-fluid state - is this what
they call deflocculation? Sometimes stirring helped, but not always and I
had to add more water. By the end, I think perhaps the glaze was a little
thin (although at that stage I only had one pot left fortunately.) Anyway,
the application looked quite thick, but now that it has dried overnight, it
doesn't look so thick anymore.
I'd just like an indication of whether this is normal or not.
Thanks,
Andrew.
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lee love on thu 1 jun 06
Andrew,
Do you wash the ash? The soluables might be helping cause the
problem.
--
Lee in Mashiko, Japan
"Let the beauty we love be what we do." - Rumi
Elizabeth Priddy on thu 1 jun 06
I have seen that problem. I have one glaze that does
it. It, in my experience, is not going to "lay down"
and fit when you fire it. It is going to leave jigsaw
puzzle looking crawling with empty spots.
Maybe at cone 10 you can get it to melt togetherm, but
why?
There is something wrong. If the work is bisqued, you
should wash it off into one clean bucket (where you
can reclaim it) and then dry the bisque and glaze it
again.
A glaze like that seems to do very well in once fire
situations, where it can really become one with the
clay, but it is just going to be everywhere if you
fire it like that.
To fix my glaze that was doing that, I let it settle,
scooped out all the water above the glaze parts above
and replaced the water. Then remixed and made it very
thin. Worked fine. But I came up with a better way
to apply it.
Now when I want to use that glaze, I glaze the work
green with that one, bisque as usual, then use the
overlapping glaze that I like with it and high fire.
So you can use a combination of once and glost fire
techniques on the same work and it works fine.
Good luck, that's all I got that might help.
E
Elizabeth Priddy
Beaufort, NC - USA
http://www.elizabethpriddy.com
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Ron Roy on thu 1 jun 06
Hi Andrew,
Your glaze is flocculated - from the solubles in your ash. If you wash it
to get rid of the solubles your glaze will change.
I would recommend a deflocculant - Darvan 7 for instance - but be careful -
if you delock too much it won't stay suspended.
The cracking is because there is too much water and too much shrinkage.
Adding clay made it worse (more shrinkage) and affected the melt as well.
Adding Darvan a drop at a time - and stirring will get you there I think -
best to do a small amount and keep track of how many drops - so you know
how much to add to the big batch.
The advantage of using a product like Darvan - it is not so easy to over do it.
RR
>I just want to know whether this is normal or not. I have an explanation
>and pictures here:
>
> http://potterboy.blogspot.com/
>
>In summary, I use an ash glaze - 50/50 ash and potash feldspar. Last time
>it cracked and left the pot all over the place - in fact, I think it must
>have lept off my pots in the kiln as it went everywhere and some times
>unexpectedly.
>
>Anyway, this time I added about 10% china clay too, as I'd read this would
>help it bond - but now I'm thinking 'bond' here means during firing, as
>although it is a little better, the pots are all cracked and flakey.
>
>The glaze also readily went in to a, well, non-fluid state - is this what
>they call deflocculation? Sometimes stirring helped, but not always and I
>had to add more water. By the end, I think perhaps the glaze was a little
>thin (although at that stage I only had one pot left fortunately.) Anyway,
>the application looked quite thick, but now that it has dried overnight, it
>doesn't look so thick anymore.
>
>I'd just like an indication of whether this is normal or not.
>
>Thanks,
>Andrew.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Andrew Douglas on sat 3 jun 06
Thanks to all that replied to my question. I fired the pots and the results
are in the usual place:
http://potterboy.blogspot.com/
Lee is right - I didn't wash the ash. I don't have a lot of space for
drying ash which is why I've had a load in a bucket of water for nearly 6
months now. And the British weather doesn't help! But I will persevere
with drying it as I think that's probably most of the problem. And the do
some more glaze tests, I think.
The fired pots show a variety of faults although I have to admit I could
live with some of them. My cone-based firing seems to have shown that my
kiln is not telling me the truth about temperature in the kiln, although I
had trouble seeing the cones and only got to cone 9 - just as well it seems
as the glaze had gone runny at that point. Why, in a yellow hot kiln, would
you make the cone-10 cone yellow in colour? It became completely invisible,
although I doubt it was that colour at the time.
Oh well - you live and learn. I'm off to my supplier today, to buy new kiln
shelves and a bottle of deflocculant.
Thanks again - you've made lots of great suggestions (as ever - clayart is a
real gem of a group) and I'll try as many as I can - it's all part of the
fun of it.
Kind regards,
A.
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Wayne Seidl on sat 3 jun 06
Andrew:
I'm going to go out on a limb here (my favorite place :>) and assume you =
are
firing an electric or gas kiln?
Take a baking pan or an old dish, pour in some of that wet ash mix from =
that
bucket (no more than 1/2 inch or so (13 mm) and set it on top of the =
kiln
while you bisque. Voila, dry ash by the time your bisque fire is done. =20
Allowing the ash to settle unmolested into the bottom of the bucket for =
a
day or two will allow you to decant some of the water from the top =
first,
and make it easier for you to remove only "the good stuff".
Just a thought.
Best,
Wayne Seidl
snip
Lee is right - I didn't wash the ash. I don't have a lot of space for
drying ash which is why I've had a load in a bucket of water for nearly =
6
months now. And the British weather doesn't help! But I will persevere
with drying it as I think that's probably most of the problem. And the =
do
some more glaze tests, I think.
snip
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