Cindy Hart on sat 29 nov 03
Hello,
I am having a problem with hairline cracking in square tiles 7.5 X 7.5".
I slab roll and cut them out. They are approx 1/2" thick. I lay them on
sheet rock and cover them with sheet rock. Each day I turn them over and
recover. I bisque fired 5 of them yesterday and all but one has a hairline
crack through it. There was no evidence of a crack when I loaded them. I
did fire them on top of each other. Could that be a problem? I fire my
smaller frames that way and haven't had any trouble. Does anyone have any
suggestions that may help prevent this?
I thought I might have a problem with the glaze firing and added Alumina
Hydrate to my wax as was suggested in the archives but these didn't even
make it that far.
TIA,
Be Well,
Sid in SC
Cindy Hart on sat 29 nov 03
Hello,
I just started reading the messages after I posted my question regarding
cracking tiles and saw the other cracking tile query. We had a lot of wet
weather here also.... I do not roll my clay at different angles and will
try that. I impress them with leaves, pine and herbs so,for me,the
thickness is not drastic. I forgot to mention that I fire to cone 6 and
bisque to cone 06.
Thanks again,
Sid in SC
Michael Wendt on sat 29 nov 03
It sounds to me like the classic stack dunting due to thermal differential.
When you fire large flat things stacked flat, the center first lags the
edges in temperature going up and if that doesn't crack them, then the
center stays hot while the edges cool causing the tiles to crack.
Standing tiles up on edge in a circular pattern that presents flat vertical
faces to the heat source ( the elements of the kiln ) allows you to fire
tiles in tight stacks without this problem as long as they don't get so hot
they warp. "Circle up the wagons" pattern so to speak
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
wendtpot@lewiston.com
www.wendtpottery.com
Sid in SC wrote:
>Hello,
I am having a problem with hairline cracking in square tiles 7.5 X 7.5".
I slab roll and cut them out. They are approx 1/2" thick. I lay them on
sheet rock and cover them with sheet rock. Each day I turn them over and
recover. I bisque fired 5 of them yesterday and all but one has a hairline
crack through it. There was no evidence of a crack when I loaded them. I
did fire them on top of each other. Could that be a problem? I fire my
smaller frames that way and haven't had any trouble. Does anyone have any
suggestions that may help prevent this?<
LindaBlossom on sat 29 nov 03
Sid,
First problem is that stacking thing. You are not allowing moisture to get
out when you stack and fire them this way. Fire them on setters or
vertically if you can and allow space between them.
I know the sheetrock drill but if you have a proper clay body this is
unnecessary. You can dry them stacked, pressed together lightly, over a
heat source and have them dry the next day if you use the right clay body.
I have done this for years without a problem.
Linda
Ithaca, NY
>
> I am having a problem with hairline cracking in square tiles 7.5 X 7.5".
>
> I slab roll and cut them out. They are approx 1/2" thick. I lay them on
> sheet rock and cover them with sheet rock. Each day I turn them over and
> recover. I bisque fired 5 of them yesterday and all but one has a
hairline
> crack through it. There was no evidence of a crack when I loaded them. I
> did fire them on top of each other. Could that be a problem? I fire my
> smaller frames that way and haven't had any trouble. Does anyone have any
> suggestions that may help prevent this?
> I thought I might have a problem with the glaze firing and added Alumina
> Hydrate to my wax as was suggested in the archives but these didn't even
> make it that far.
.
Gordon Ward on sat 29 nov 03
I have been firing tiles on edge making sure there is air space around
each tile. By starting in the center of the shelf with a kiln post as a
support, I begin placing the tiles on either side, fanning out in a
herringbone pattern with only the tile's corner touching it's neighbor for
balance. Some clay bodies seem to be better than others too, so
some testing may also be in order. Good luck.
Gordon
Janet Kaiser on sun 30 nov 03
Hi Terry!
When you say that there has not been the problem before, is that
with tiles of the same design? Have the tiles a thick "border" of
clay, or is the carving right up to the edge? Before you
soul-search too much about the clay, moisture retention, firing,
cooling, etc. I would look at the tiles themselves, if I were
you. It takes a lot of skill and a steep learning curve to "carve
clay" successfully, as you are no doubt aware. I worry that this
artist is doing something quite "advanced" without the necessary
basics in place...
You say that there is "fairly deep relief carving", which IMHO is
the potential problem here... The tensions between thick and thin
areas are massive, albeit on a very small scale relative to, say,
a very large pot... But as when it is not a good idea to have
very thick to exceedingly thin areas on a vessel, the same goes
for flat ware such as tiles. Possibly even more so, as warping
and cracking occur more often in tiles than in vessels,
sculptures, etc. As in sculpture, cracks are inevitable unless it
is a very well-grogged body, when you MAY just get away with such
a technique/design for tiles.
Perhaps a solution would be to have the artist carve a negative
form, biscuit fire that and then use it as a stamp? Being a
graphic artist, they should not have any difficulty working in
reverse or negatives.
Alternatively, the total THICKNESS of tiles needs to be
increased, so that (say) the bottom 1/2 inch is a "base" which
may not be reduced and then the 1/4 to 1/2 inch top half can be
regarded as the "carvable" part.
Otherwise, I think that they need to start slowly, gradually
increasing the depth until they find the limits of the material
they are using for themselves. Clay being a new medium for them,
you may even need to impress upon them, that they are trying to
do something "extreme", to which the medium (i.e. clay) is not
really suited. If they do not want to waste a lot of time and
work "experimenting", they could do with learning some of the
"ground rules" before trying to stretch the material's inherent
properties. Crawling before walking before running, if you get my
drift?
Hope this helps to bring all possible causes into the equation
for consideration!
Janet
*** IN REPLY TO THE FOLLOWING MAIL:
>One of our folks here at Nottingham is moving from graphics to
art deco
>carved tiles. She is using a sanded white cone 10 stoneware
clay from
>Ardvark ( Hopkins White standard ). These tiles are 1/2 - 3/4
inch
>thick often with fairly deep relief carving.
>Problem with her last batch of tiles was craking which remained
fairly
>thin and had the glaze healed over the cracks. Tiles were glazed
bisque
>right after a long rainy week and fired on a slow Skutt cone 6
program.
>The clay is rolled several times at opposite angles using a
Baily slab
>roller and the tiles are dried very slowly. This is the first
time the
>problem has occured.
>My thought is that the tiles contained lots of moisture from
the week
>of high ambient weather and fairly heavy glazing ( three brushed
on
>coats) and cracked due to too fast a firing.
*** THE MAIL FROM terry sullivan ENDS HERE ***
***********************************************************
The top posted mail was sent by Janet Kaiser
The Chapel of Art : Capel Celfyddyd
8 Marine Crescent : Criccieth : Wales : UK
Centre of Excellence for The Arts
Home of The International Potters' Path
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Llewellyn Kouba on sun 30 nov 03
Hello Cindy,
I had some of the same problems Cindy with slab rolling. I really think
this is the problem or at least was my issue. I was doing large pieces of
slab - 9 x 13 (larger really because I had to cut the excess off to square
the tile). Where I would join hunks of clay together here is where the
problem comes in. Even though you don't see the cracks they are in the
joined sections. I found scoring and slipping the joined sections before
pressing or rolling helps but may not eliminate the problem altogether? My
next solution is: I made a mold of my tile and now will use fairly smooth
(more slip like) pour or press into the plaster mold and it should be one
unit and also add more grog will also help. It will take longer to dry but
I hope for better results. I don't know if this is a help but something I
learned from my last tile project.
Llewellyn Kouba
At 09:57 AM 11/29/2003 -0500, you wrote:
>Hello,
>
>I am having a problem with hairline cracking in square tiles 7.5 X 7.5".
>
>I slab roll and cut them out. They are approx 1/2" thick. I lay them on
>sheet rock and cover them with sheet rock. Each day I turn them over and
>recover. I bisque fired 5 of them yesterday and all but one has a hairline
>crack through it. There was no evidence of a crack when I loaded them. I
>did fire them on top of each other. Could that be a problem? I fire my
>smaller frames that way and haven't had any trouble. Does anyone have any
>suggestions that may help prevent this?
>I thought I might have a problem with the glaze firing and added Alumina
>Hydrate to my wax as was suggested in the archives but these didn't even
>make it that far.
>
>TIA,
>Be Well,
>Sid in SC
>
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