Cindy Hart on tue 7 sep 04
Hi all,
I am suddenly having a problem with my clay blistering (overfiring) during
glaze and am wondering if anyone else is having that problem. I use
Miller, now Laguna, #66, or WC610. I have been using this clay for about
10 years and this has never happened. My last 3 firings have produced
bloated product. I bisque to 06. At the end of my last firing I did not
even let cone 6 get to a 1/4 bend and I still had blisters but not on all
the product... I cannot fire lower as my glaze is still cloudy at cone 5,
plus this is not the only clay I use. My other clay products are not
affected at all ( Miller/Laguna 50 WC606. )
I have a friend who also uses this clay (#66) and has had no problems but I
can't think of anything else it can be except the clay(???) I haven't
changed any of my usual firing practices and none of my other products are
affected.....
I have called Laguna and they are checking the batch but they also have
heard no problems at all. Any ideas??
TIA,
Cindy in SC
MarjB on wed 8 sep 04
Morning Cindy
If you can break one of your bloated pieces to get a chunk that has no
glaze, larger the better, weigh it then boil for 2 hours. Then re-weigh.
That will give you a quick test if your clay is overfiring. You can do more
accurate tests with the claybody in next firing.
If it appears that your body is not completely vitrified then look to your
bisque firing. Supplier may have changed one of the clays in formula and
there may be more organic materials that need a slower bisque during the
carbon burn out phase. In other words it might not be overfired but you
have carbon trapped within the clay body. A slightly higher bisque temp
could also assist and if you have a fan that will draw air from the kiln
during the bisque that will also help. Example: I have an overhead hood/fan
and leave top peep open.
Hope these suggestions help.... or welcome to the club of changed clay
bodies and all the work that that entails. MarjB
----- Original Message -----
From: "Cindy Hart"
To:
Sent: Tuesday, September 07, 2004 5:30 PM
Subject: clay blistering
Mark Strayer on wed 8 sep 04
Perhaps your thermocouple needs replacing?
>-- Original Message --
>Date: Tue, 7 Sep 2004 17:30:03 -0400
>Reply-To: Clayart
>From: Cindy Hart
>Subject: clay blistering
>To: CLAYART@LSV.CERAMICS.ORG
>
>
>Hi all,
>
>I am suddenly having a problem with my clay blistering (overfiring) duri=
ng
>glaze and am wondering if anyone else is having that problem. I use
>Miller, now Laguna, #66, or WC610. I have been using this clay for abou=
t
>10 years and this has never happened. My last 3 firings have produced
>bloated product. I bisque to 06. At the end of my last firing I did no=
t
>even let cone 6 get to a 1/4 bend and I still had blisters but not on al=
l
>the product... I cannot fire lower as my glaze is still cloudy at cone
5,
>plus this is not the only clay I use. My other clay products are not
>affected at all ( Miller/Laguna 50 WC606. )
>I have a friend who also uses this clay (#66) and has had no problems bu=
t
>I
>can't think of anything else it can be except the clay(???) I haven't
>changed any of my usual firing practices and none of my other products
are
>affected.....
>I have called Laguna and they are checking the batch but they also have
>heard no problems at all. Any ideas??
>
>TIA,
>Cindy in SC
>
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nk.com.
Ron Roy on fri 10 sep 04
Hi Cindy,
I have looked the clay up in the Laguna catalogue - a white stoneware with
sand - sounds like the clay is not good for the cone (6) it is advertized
for - I would at least expect it to be replaced.
If they are testing their clay it should show up in their data.
If you are dealing with a clay company that does not test their clays - you
will need to test any new clay as you buy it to be sure it will work
properly.
If you need instructions on how to test clay let me know.
RR
>I am suddenly having a problem with my clay blistering (overfiring) during
>glaze and am wondering if anyone else is having that problem. I use
>Miller, now Laguna, #66, or WC610. I have been using this clay for about
>10 years and this has never happened. My last 3 firings have produced
>bloated product. I bisque to 06. At the end of my last firing I did not
>even let cone 6 get to a 1/4 bend and I still had blisters but not on all
>the product... I cannot fire lower as my glaze is still cloudy at cone 5,
>plus this is not the only clay I use. My other clay products are not
>affected at all ( Miller/Laguna 50 WC606. )
>I have a friend who also uses this clay (#66) and has had no problems but I
>can't think of anything else it can be except the clay(???) I haven't
>changed any of my usual firing practices and none of my other products are
>affected.....
>I have called Laguna and they are checking the batch but they also have
>heard no problems at all. Any ideas??
>
>TIA,
>Cindy in SC
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Gaye Sekula on fri 10 sep 04
Ron,
If you don't mind, I would appreciate the instructions on how to test clay.
I, too, have a white clay with sand that is giving me fits.
Thanks, Gaye
In a message dated 9/10/2004 6:02:38 AM Central Standard Time,
ronroy@CA.INTER.NET writes:
If you need instructions on how to test clay let me know.
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