vivek patel on tue 25 dec 01
(long) India
Wishing you all a very Merry Christmas and a Happy and
Prosperous New Year.
Actually I am into manufacturing saltglazed sewer
pipes and decorative saltglazed tiles in India. I fire
these in huge downdraft kilns of 24 to 30 feet in
diameter. These kilns are fired with coal. Lately I
have been experiencing the problem of crazing on my
tiles and the tiles are fired as whole boxes and then
after firing they are split into tiles. I load a
square box of four tiles which are to be split after
firing.
THE CRAZING ON THE TILES CAN BE CLEARLY SEEN IN THE
PHOTO IN THE ZIP FILE WHICH IS ATTATCHED. THERE ARE 4
OR 5 TILES OF DIFFERENT SIZES. THE CRAZING IS NOT VERY
DEEP AND IF YOU BREAK THE TILE YOU CAN SEE THAT THE
CRAZING IS DEEP ONLY TILL THE LAYER OF THE GLAZE OR
PROBABLY A FRACTION DEEPER BUT IT CERTAINLY LOOKS
UNATTRACTIVE TO THE BUYERS HERE.
What could be the reason for this crazing.
1...Of late I have been telling my people to very
slowly cool the kiln andthe cooling has been very slow
and I open my fire boxes and the holes at the top on
my kiln very late late by 24 to 30 hours. But still I
get this crazing.
2... I took out 2 kilnloads of tiles which were dipped
in a slip before they were fired. they came out fine
without a single crack or crazing. But again I havent
gotten good results. could it be because of the slip.
The slip is 25% quartz,25% feldspar,15% China Clay
Kaolin, 35% black fireclay, . To this mixture I added
1% red iron oxide powder. This slip gave out wonderful
results. A very rich orange to brown colour. The
crazing didnt happen in two kilns but thereafter I
have been getting crazing. could it be because of the
mismatch of the body and the slip. But if thats the
case I woulnt have gotten two kilnloads of non crazed
tiles. AND I FIRED A KILN RECENTLY WITHOUT DIPPING THE
TILES IN THIS SLIP AND I AM STILL GETTING CRAZING.
THE BODY OF MY TILES IS 90% BLACK FIRECLAY AND 10%
GROG. IT ALWAYS GIVES GOOD RESULTS BUT EVEN THE LAST
TWO KILNS WHICH WERE FIRED WITH TILES WITHOUT THE SLIP
IT GAVE OUT CRAZING. IN THESE KILNS THE HOLES ON THE
TOP OF THE DOME OF THE KILNS WERE OPENED 24 TO 36
HOURS LATER THAN NORMAL. THE TILES HAVE CRAZED
3....The crazing is more profound or visible on the
tiles near the fire boxes where the temperature might
be high. Might that be the cause?(overfiring) but it
doesnt seem so. I have gotten perfect kilns using the
same firing techniques before.
4.... It seems that the crazing appears befor the
salting because if I break the tile and see the cross
section it appears that the salt has entered through
the crack just very slightly into the body hardly 1/2
mm. but I might be wrong.
5... Could it be the shape of the wares. My pipes are
round and they hardly receive any crazing. THE tile
boxes are like hollow square boxes. But then some
pipes do receive crazing but that is very rare and to
a lesser extent
What has me worried is that I cant find the exact
cause. CAN IT BE VERY SLOW COOLING BECAUSE I HAVE
NOTICED THAT I GET CRAZING IN THE KILNS BECAUSE I HAVE
ASKED THESE KILNS TO BE COOLED AT A VERY SLOW RATE 24
TO 36 HOURS LATER THAT MOST OF THE EARLIER FIRED KILNS
I KNOW THIS IS A VERY LONG MAIL BUT IF ANYONE COULD
ANSWER TO THIS IN DETAIL IT WOULD BE VERY HELPING. I
AM VERY CONFUSED.
Vivek Patel from India
Thanking you
__________________________________________________
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Send your FREE holiday greetings online!
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Tony Ferguson on wed 26 dec 01
(long) India
Could you please send some pics directly to me or post them on something
like Yahoo picture galleries where we all can look at them? Or if you have
a web site, post them there?
Thank you.
Tony Ferguson
315 N. Lake Ave. Apt. 401
Duluth, MN 55806
USA
218.727.6339
Stoneware, Porcelain, Raku
http://www.AquariusArtGallery.com
----- Original Message -----
From: "vivek patel"
To:
Sent: Tuesday, December 25, 2001 10:55 PM
Subject: Help urgently needed for crazed saltglazed tiles photo attatched
(long) India
> Wishing you all a very Merry Christmas and a Happy and
> Prosperous New Year.
> Actually I am into manufacturing saltglazed sewer
> pipes and decorative saltglazed tiles in India. I fire
> these in huge downdraft kilns of 24 to 30 feet in
> diameter. These kilns are fired with coal. Lately I
> have been experiencing the problem of crazing on my
> tiles and the tiles are fired as whole boxes and then
> after firing they are split into tiles. I load a
> square box of four tiles which are to be split after
> firing.
> THE CRAZING ON THE TILES CAN BE CLEARLY SEEN IN THE
> PHOTO IN THE ZIP FILE WHICH IS ATTATCHED. THERE ARE 4
> OR 5 TILES OF DIFFERENT SIZES. THE CRAZING IS NOT VERY
> DEEP AND IF YOU BREAK THE TILE YOU CAN SEE THAT THE
> CRAZING IS DEEP ONLY TILL THE LAYER OF THE GLAZE OR
> PROBABLY A FRACTION DEEPER BUT IT CERTAINLY LOOKS
> UNATTRACTIVE TO THE BUYERS HERE.
> What could be the reason for this crazing.
> 1...Of late I have been telling my people to very
> slowly cool the kiln andthe cooling has been very slow
> and I open my fire boxes and the holes at the top on
> my kiln very late late by 24 to 30 hours. But still I
> get this crazing.
>
> 2... I took out 2 kilnloads of tiles which were dipped
> in a slip before they were fired. they came out fine
> without a single crack or crazing. But again I havent
> gotten good results. could it be because of the slip.
> The slip is 25% quartz,25% feldspar,15% China Clay
> Kaolin, 35% black fireclay, . To this mixture I added
> 1% red iron oxide powder. This slip gave out wonderful
> results. A very rich orange to brown colour. The
> crazing didnt happen in two kilns but thereafter I
> have been getting crazing. could it be because of the
> mismatch of the body and the slip. But if thats the
> case I woulnt have gotten two kilnloads of non crazed
> tiles. AND I FIRED A KILN RECENTLY WITHOUT DIPPING THE
> TILES IN THIS SLIP AND I AM STILL GETTING CRAZING.
> THE BODY OF MY TILES IS 90% BLACK FIRECLAY AND 10%
> GROG. IT ALWAYS GIVES GOOD RESULTS BUT EVEN THE LAST
> TWO KILNS WHICH WERE FIRED WITH TILES WITHOUT THE SLIP
> IT GAVE OUT CRAZING. IN THESE KILNS THE HOLES ON THE
> TOP OF THE DOME OF THE KILNS WERE OPENED 24 TO 36
> HOURS LATER THAN NORMAL. THE TILES HAVE CRAZED
> 3....The crazing is more profound or visible on the
> tiles near the fire boxes where the temperature might
> be high. Might that be the cause?(overfiring) but it
> doesnt seem so. I have gotten perfect kilns using the
> same firing techniques before.
> 4.... It seems that the crazing appears befor the
> salting because if I break the tile and see the cross
> section it appears that the salt has entered through
> the crack just very slightly into the body hardly 1/2
> mm. but I might be wrong.
> 5... Could it be the shape of the wares. My pipes are
> round and they hardly receive any crazing. THE tile
> boxes are like hollow square boxes. But then some
> pipes do receive crazing but that is very rare and to
> a lesser extent
>
> What has me worried is that I cant find the exact
> cause. CAN IT BE VERY SLOW COOLING BECAUSE I HAVE
> NOTICED THAT I GET CRAZING IN THE KILNS BECAUSE I HAVE
> ASKED THESE KILNS TO BE COOLED AT A VERY SLOW RATE 24
> TO 36 HOURS LATER THAT MOST OF THE EARLIER FIRED KILNS
>
> I KNOW THIS IS A VERY LONG MAIL BUT IF ANYONE COULD
> ANSWER TO THIS IN DETAIL IT WOULD BE VERY HELPING. I
> AM VERY CONFUSED.
>
> Vivek Patel from India
>
> Thanking you
>
> __________________________________________________
> Do You Yahoo!?
> Send your FREE holiday greetings online!
> http://greetings.yahoo.com
>
>
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