mel jacobson on mon 10 aug 98
the old story.
you can compress til your fingers bleed, and if you have a bad
clay..........cracks.
when i work anything large, i change my body.
lots of sand and grog...fine grog is fine.
but boy, my stuff just never cracks. (or if it does it is because i let
them dry in one place too long. i quess anyone that studied with mackenzie
sorta has an instinct for sand.
he just loves it.
open bodies just work.
and you can learn to throw it for most anything............those tight,
sticky, baby pooh bodies are wonderful for begginers, babies...........but
potters use open bodies.
no cracks, no loss, and they look great when you tip your bottoms over.
have you ever seen a ferguson, mackenzie bottom.............do you think
they throw
with baby poooh.?
hell, i even grog up porcelain if i am going to throw big.
mel./mn
http://www/pclink.com/melpots
marie elaine on wed 12 aug 98
> when i work anything large, i change my body.
> lots of sand and grog...fine grog is fine.
> open bodies just work.
Ok Mel... I'm taking your advise to heart... especially since I've had some
recent trouble with a white stoneware body and slip trailing.
I'd like to know what amounts and what grain size of sand have you found to
work best when throwing large forms say from 7 to 10#s of clay.
Here in back to normal hot and humid sunny florida... Marie Elaine
carrie or peter jacobson on mon 12 oct 98
Hi Paul and clayarters: As a fledgling potter, I don't get the gist of what
you're saying about adding the extra ball of clay... How big is "tiny"? Tip
of your little finger? Smaller? Does the ball go on the inside of the pot,
or the outside? I guess, if it goes on after trimming, the pot is
leather-hard? What is the point of this, and why does it work?
I've had some trouble lately with the bottoms of bowls cracking. These
aren't S cracks, generally, and I don't understand what I am doing wrong.
I'm working in porcelain, and making wide shallow bowls, like 14-16 inches
across and maybe 6" from the bottom of the foot to the lip. Lots of them
are cracking, near the foot or across the bottom of the bowl, and I don't
get it.
I'll try anything to get this to stop, and wonder if what you are
describing would help? I have only been throwing about a year, so I am a
babe in the woods.
thanks,
Carrie
--+++--
----------------------------Original message----------------------------
The best way to prevent cracks in ware thrown off the hump is to have
the bottoms be REAL thin. If you're not trimming, you should be able
to see the wire go through as you're looking down into the pot. If
you are trimming, you just need to trim real thin.. Dave Shaner has a
neat trick for this, also. He adds a tiny ball of clay in the center
of the foot after trimming and attaches it with a spin of the wheel so
it has a kind of spiral ridge shape to it. They never crack.
Paul Lewing, Seattle
-----------------------------
Carrie Jacobson
Pawcatuck, CT
mailto:jacobson@brainiac.com
Grace Epstein on sat 26 dec 98
Happy New Year and is there
anyone who knows what would cause large cracks across the diameter of large
bowls ( rim diameter of 13 " , about 9 " deep ) ? Prior to bisque firing
there is no evidence of any crack. It's not an s, nearly a straight
crack...3-4" long.
2 out of 2 Christmas gifts with cracks !
Grace
Dan Tarro on sun 27 dec 98
Grace,
This may be the same thing that I experienced a few months back. If it
is, I might be able to help. I need to know what kind of kiln you bisqued
in first.
Dan Tarro
Oak Tree Stoneware
Ham Lake, Minnesota
On Sat, 26 Dec 1998 14:19:04 EST Grace Epstein
writes:
>----------------------------Original
>message----------------------------
>
>
>Happy New Year and is there
>anyone who knows what would cause large cracks across the diameter of
>large
>bowls ( rim diameter of 13 " , about 9 " deep ) ? Prior to bisque
>firing
>there is no evidence of any crack. It's not an s, nearly a straight
>crack...3-4" long.
>2 out of 2 Christmas gifts with cracks !
>Grace
>
___________________________________________________________________
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Richard Ramirez on sun 27 dec 98
Grace,
Are you compressing bottoms and are you sure your bottoms aren't too thin?
Maybe that helps? Richard Ramirez "The Clay Stalker"
Ron Roy on sun 27 dec 98
Hi Grace,
Get the Hamer book and look under C for cracks - you will see about 10
pages of different kinds of cracks - pick out the one that looks like what
is happening to you and you will have the reason it happened.
It is important to know if the crack is open or closed when trying to
figurer out when cracks happened. It is also necessary to know if the edges
are sharp or rounded if the ware is glazed.
RR
>----------------------------Original message----------------------------
>Happy New Year and is there
>anyone who knows what would cause large cracks across the diameter of large
>bowls ( rim diameter of 13 " , about 9 " deep ) ? Prior to bisque firing
>there is no evidence of any crack. It's not an s, nearly a straight
>crack...3-4" long.
>2 out of 2 Christmas gifts with cracks !
>Grace
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Grace Epstein on tue 29 dec 98
Hi Richard the Claystalker
I know I am supposed to compress...not positive I always do so enough...any
advice would be helpful...I may be trimming down too thin ...actually I just
measured the depth of the crack at the center of the bottom: 1/4" thick !
that's not that thin is it ? Someone else had thought I had too thick of a
bottom...Either way I imagine the crack is from type of stress?
Grace
Paul & Lori Rozman - Lautermilch on wed 30 dec 98
Grace,
That's ceramics for you: the cause could be a number of things. It is
difficult to tell sight unseen. Some times there could be a hairline crack
in the green state(due to drying the edges too fast). It sounds to me
though from your description that it might be a cooling (heat shock) crack
problem. If you look at the split with a magnifying glass one can usually
tell by the edges of the split if it is a crack that occurred on the way up
or down. If the edges are covered with glaze then you had that crack on the
way up the temp. in which case it would be a drying crack. If the split is
sharp edged then it is a cooling too fast ( or heat shock) problem. Either
case you know to prevent it in the future. No short cuts in Ceramics and
don't we know it.
Happy New Year to All,
Paul Rozman
700 Russell Road, RR# 2
Ladysmith, BC, V0R 2E0
Canada
TL. (250) 245-1055
http://www3.bc.sympatico.ca/mtopottery
mtopottery@bc.sympatico.ca
-----Original Message-----
From: Grace Epstein
To: CLAYART@LSV.UKY.EDU
Date: December 26, 1998 11:19 AM
Subject: Cracks
>----------------------------Original message----------------------------
>
>
>Happy New Year and is there
>anyone who knows what would cause large cracks across the diameter of large
>bowls ( rim diameter of 13 " , about 9 " deep ) ? Prior to bisque firing
>there is no evidence of any crack. It's not an s, nearly a straight
>crack...3-4" long.
>2 out of 2 Christmas gifts with cracks !
>Grace
>
JP Shepherd on wed 30 dec 98
Do you have a good foot rim on it? I have found that I never get cracks on
the bottoms when I have a foot rim. (Sometimes I get lazy though or have
made the bottom too thin for one and it ends up ruined by the crack anyway.)
Hope that helps,
JP
-----Original Message-----
From: Grace Epstein
To: CLAYART@LSV.UKY.EDU
Date: Saturday, December 26, 1998 12:19 PM
Subject: Cracks
>----------------------------Original message----------------------------
>
>
>Happy New Year and is there
>anyone who knows what would cause large cracks across the diameter of large
>bowls ( rim diameter of 13 " , about 9 " deep ) ? Prior to bisque firing
>there is no evidence of any crack. It's not an s, nearly a straight
>crack...3-4" long.
>2 out of 2 Christmas gifts with cracks !
>Grace
>
Veena Raghavan on wed 30 dec 98
Grace,
At the risk of sticking my neck out, when there are so many more
experienced and expert potters in Clayart, I have found that having the
thickness of the bottom and the sides as equal as possible makes a big
difference. I have had students, who make thick bottoms, but the sides are
thinner, especially near the foot, and the result is cracking. I have also
found that, apart from compressing when one is throwing, it is very
important to keep sponging out the water so that the bottom does not get
water-logged, this is another problem I have had with students. Thirdly, I
think it helps to compress the bottom from the outside, when the piece is
leatherhard, but burnishing it with the end of a wooden tool or spoon.
Hope some of this helps.
All the best and Happy New Year.
Veena
Veena Raghavan
75124.2520@compuserve.com
Grace Epstein on thu 31 dec 98
Paul
I will definately look at the cracks...I do tend to rush the bisque
cooling...esp when trying to get pieces into christmas packaging...AND drying
too fast may definately may be a problem esp when one day the woodstove is on
and the next day it is not...
thanks for your help
its surprising how many people have been dealing with cracks !
grace
in CT where we have snow ! beautiful to see and awful to drive in
Grace Epstein on thu 31 dec 98
jp
lately the foot rim i make is just the result of trimming out the bottom out
to about 1/4" away from the sides of the bowl...a foot that is only visable
when holding the pot upside down ( wish i had a pencil )
grace
Burtt on thu 31 dec 98
Hi Grace and others:
I've been dealing with bottom cracks for some time now and feel
certain that my problems go back to drying time.
Since I work out of my garage, I also dry my pots in the garage,
making them subject to the weather. I live on the Gulf Coast where we
have extremes of humidity, but also some very dry weather at times.
During a recent prolonged spell of high humidity, I had no
cracks...zero. But then a colder dry front moved through and some of my
cracks returned. I have put extra emphasis on the bottoms of my pots and
that helped some, but some of my questions for others out there are
these:
Am I crazy for trying to dry in my garage?
When is the critical time for drying? I dry quickly from wheel to
leather hard, then I trim and cover them with plastic.
Is there a system for how long to cover? I do not leave them covered
until bone dry. Should I?
Just a few questions as I try to ``crack'' one more production
problem.
Thanks and good luck, Grace.
Steve Burtt
Grace Epstein on thu 31 dec 98
Veena
I like your idea of thin sides and thick bottoms...I am new at throwing larger
pieces and I am sure the last 1-2" near the bottom are thick...there has to be
some kind of pulling -stress action to result in the crack. I will take heed
of all of your ideas as any one of them may contribute !
thanks
Grace
Joyce Lee on fri 1 jan 99
Usual disclaimer: I'm not even close to an expert.......but....
the "thin sides/thick bottom" comments sound reasonable for me, too. My
last "angel eyes" (sorta' tenmoku) 6" high/11" wide bowl has two cracks
in the middle part of the foot ring. The clay body has limited grog.
Luckily, I'm able to use it because the cracks don't go through and the
glaze breaks nicely around&in the cracks so they look almost
planned...IF my names both began with "S", that is. I haven't
experienced many cracks, but this bowl is both thinner than I usually
throw and much thicker on the bottom. Best I could do that day so I
kept it. Looks great piled with lemons.
Joyce
In the Mojave going out to torture the clay and further punish the
extruder, which is beginning to regret coming to live at my house. I
think in addition to a directionality disability (tested), I must be
spatially challenged, also. I am amazed at the shape of the extrusions
so far...evidently need physical evidence/end-product in order to fully
comprehend ("see) shapes...then light bulb flickers and it's "ooohhh, so
that's it" time...until then, don't know what to expect.
Antoinette Badenhorst on mon 28 jun 99
Carrie, Are these cracks spiraling around the pot? Do you sometimes
feel that your hands are too quick for your wheels rotation. Increase
your speed then, because you might stretch the clay beyond its limits.
Do you throw thick and trim thin? If so, do you compress the pot again
after you have trimmed? You should also work with very sharp trimming
tools on porcelain. Porcelain is normally drier than other clay when
one trim , which means that the pressure that one put onto it when
trimming is critical. If your tools are sharp it help to decrease
pressure and the possibility to crack the pot without knowing it. I
never tested for cracks on green porcelain before, so I do not know if
it will work, but if you paint paraffin on any other greenware before
bisque firing, it shows the cracks clearly. It might be worth a try on
your porcelain.
Enjoy your porcelain!
Antoinette
--- carrie or peter jacobson wrote:
> ----------------------------Original
> message----------------------------
> All you experts out there: I have read the archives,
> and have even done
> what they said to do, but it ain't workin'.
>
> I am starting to make some pretty nice stuff, in
> porcelain, and am also
> starting to have problems with cracks. I have solved
> the bottom-cracking
> issues. These cracks start at the foot. Some cross
> the foot, some go up the
> side of the foot and onto the wall of the piece, and
> one traveled across
> the foot and onto the bottom of the bowl, but was
> not an s-crack.
>
> I have tried mending these with paper clay, and been
> somewhat successful.
> But most of the last pieces have not shown cracks
> until I pull them out of
> the glaze firing.
>
> I'm using commercial cone 6 porcelain, I am turning
> the clay sideways
> after wedging (i.e., not putting the pointy end of
> the wedged piece facing
> up). I am compressing the bottoms. I am, at least
> now, not single-firing.
> (Interestingly, this particular problem did not
> occur when I did single
> fire. Then, I had other problems.) My one insight is
> that my pieces are
> quite thin now, though the feet are thicker. I
> wonder if there is too much
> tension there?
>
> I am drying these things very slowly, wrapping in
> plastic, not using
> plastic bats, turning them over when they are dry
> enough. Is there such a
> thing as drying too slowly?
>
> Thank you in advance for your help.
>
> Carrie
>
>
> Carrie Jacobson
> Pawcatuck, CT
> mailto:jacobson@brainiac.com
>
===
Antoinette Badenhorst
PO Box 552
Saltillo,Mississippi
38866
Telephone (601) 869-1651
timakia@yahoo.com
_________________________________________________________
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Get your free @yahoo.com address at http://mail.yahoo.com
Jeri Palmer on mon 28 jun 99
Carrie, I work in ^10 porcelain and I have had the cracks you are getting,
but only once or twice. Please put the pointy end up you just spent all that
effort aligning all those platelets, don't go against them now. Also, your
pot needs to be the same thickness all over. I can't stress this enough. I
love to work very thin but any time your piece goes from thick to thin or
vice versa you got troubles. Try to keep the bottom and the foot the same
thickness as your wall. I will make a big difference. Jeri
John K Dellow on mon 28 jun 99
carrie or peter jacobson wrote:
>
>
> I am drying these things very slowly, wrapping in plastic, not using
> plastic bats, turning them over when they are dry enough. Is there such a
> thing as drying too slowly?
>
> Thank you in advance for your help.
>
> Carrie
>
> Carrie Jacobson
> Pawcatuck, CT
> mailto:jacobson@brainiac.com
-- Try using cloth to cover the pots when slow drying. Plastic can cause
moisture to condense on the inside and drip back onto the pots. This may
cause fine cracks which will not be apparent until after the glaze
firing.
John Dellow "the flower pot man"
ICQ : #2193986 {jacka}
E-mail : dellowjk@kewl.com.au
25 Hugh Guinea Ct, Worongary Q 4213
Ph:+61-7-55302875 Fax:+61-7-55253585
Home Page http://www.welcome.to/jkdellow
Mike Bailey on mon 28 jun 99
In message , carrie or peter jacobson writes
Dear Carrie,
Snip
>
>These cracks start at the foot. Some cross the foot, some go up the
>side of the foot and onto the wall of the piece, and one traveled across
>the foot and onto the bottom of the bowl, but was not an s-crack.
Snip
What temperature are you using for the bisque? - it could be that you
are underfiring at this stage - this is one of the main reasons for this
sort of cracking. It sounds like a form of dunting.
Cheers.
Mike.
--
Mike Bailey. Bath. U.K.
Ron Roy on tue 29 jun 99
Hi Carrie,
This may be bisque dunting caused by the free silica in the body. The
quartz (silica) goes through an inversion at 573C on the way down and if
one part of the pot goes through the inversion faster than the other part
dunting can occur.
The clue - if it is bisque dunting - the crack will be closed when you open
the kiln. If you could see the ware as the cracking is happening - the
crack would be open - as the rest of the ware goes through the inversion
temperature - the crack will close up.
Part of the solution is to fire the bisque higher - I assume you are firing
it below 04 - try it at 04 - makes the ware stronger.
Another solution is to slow down the cooling at the crucial time - like
between 650C and 500C - and/or making sure your kiln is well sealed -
certainly turn off any venting system. Densely stacked bisque kilns will
cool slower and may prevent the uneven cooling enough to prevent this kind
of dunting.
Kilns usually cool faster at the bottom - so you may notice this cracking
more at the bottom of your bisque loads.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
mel jacobson on tue 20 jul 99
as you age you see pots in people's homes that you would
pay any price to get back...then take them home and hammer
them to bits. and they are your pots.
i have paintings out there that i am plotting a break in
robbery, to get them back, so that i may burn them.
of course if anyone robbed me of my sheila clennell cups and saucers
i would track them down and use my 30/30 on them.
so, be careful about bad flaws.....they have a way of biting you
in the butt.
and it hurts.
on the other hand, went to lunch and saw some blue bowls that i made
in 1970 that i thought were really nice...man, did i do that?
20 inches across....damn....makes one think.
mel/mn
http://www.pclink.com/melpots
from minnetonka, minnesota, u.s.a.
Vivian Mills on thu 30 mar 00
------------------
On a recent trip to China, I came home with a Yixing teapot. When I got it =
home,
I discovered it had a hairline crack down from the open top of the pot, and
unfortunately, it leaks .
Does anyone have any suggestions as to how I might repair this, and make it
useable. Could I maybe put a bit of low-fired glaze on the inside over the
crack, and refire it to a low temperature?
It is a dark red-brown color now, stoneware, and unglazed. Thanks for your
ideas.
Vivian
Cindy Strnad on fri 31 mar 00
Vivian,
What a bummer! I think I would apply some paper clay to the crack, and then
glaze with a clear glaze, just over the crack. If you glaze only, the
chances are good that your glaze will just seep into the crack and leave you
with a teapot that still leaks. I've fixed cracks using the paperclay
method, and it's always worked just fine for me, and doesn't even show. I
stick with ^6 glazes, but I expect your idea of using a low-fire glaze might
be safer for the pot.
Cindy Strnad
earthenv@gwtc.net
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
Diane G. Echlin on mon 7 aug 00
Ugh! I unloaded some bisque this morning and found some cracks in the
bottoms of my bowls. there were three different kinds: s-cracks which I
understand come from poor compression of the bottom of the form, then a
double Y crack that looks like this (I hope it translates well:)
\___/
/
and a three-pronged crack like this:
/
_____/
I'm using ^6 Laguna/Miller white stonware, and I think this might have
been a batch of reclaim, or reclaim mixed with fresh out of the bag.
thanks in advance!
Diane in CT
philrogers pottery on mon 7 aug 00
Diane,
These are 'biscuit dunts' caused by not reaching a high enough
temperature.in the biscuit firing. Typically these cracks can resemble brick
work in their appearance. Clay requires to reach a high enough temperature
to provide the strength to withstand the rigours of cooling. This
temperature varies a little according to the clay but Cone 06 is a
reasonable average. This temp. must be attained throughout the kiln so a
slow temp.rise at the end and then a soak would probably be beneficial.
Please refer to Frank Hamers excellent Dictionary of Potters Materials and
Techniques for a fuller explanation.
Phil Rogers.
----- Original Message -----
From: Diane G. Echlin
To:
Sent: Monday, August 07, 2000 3:16 PM
Subject: cracks
> Ugh! I unloaded some bisque this morning and found some cracks in the
> bottoms of my bowls. there were three different kinds: s-cracks which I
> understand come from poor compression of the bottom of the form, then a
> double Y crack that looks like this (I hope it translates well:)
> \___/
> / >
> and a three-pronged crack like this:
> /
> _____/
> > >
> I'm using ^6 Laguna/Miller white stonware, and I think this might have
> been a batch of reclaim, or reclaim mixed with fresh out of the bag.
> thanks in advance!
> Diane in CT
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
mel jacobson on fri 1 dec 00
there are many experts on this list that can go
into some detail about cracks. i hope they do.
i have always used the simple explanation that
clay is under tension when in the drying stage...when
you fire, well it just increases the tension. crack.
once the crack happens, the tension is released.
try and figure out why the tension is there. then do
something about it....throwing, building, drafts, uneven
drying...all contribute.
in most cases, the shape of the crack and where it occurs
will aid you in finding the reason. (experts, please)
same with a kiln shelf, once it cracks and relieves its
tension....hell you can use it for 40 years. it will crack
no further.
mel
just plain ol` mel. works for me.
charles pearce, the fine lettering artist designed
my enclosure card for me as a gift. he used the term `master potter`.
he said he stands by the term. so be it.
the only thing mr. uchida gave me when i left the pottery in kyoto
was a stamp....it was `sama`*. it means a great deal to me...no
one else.
*sama, loosly translated means `Most Honorable Mister.`
FROM MINNETONKA, MINNESOTA, USA
http://www.pclink.com/melpots (website)
Earl Brunner on fri 19 jul 02
I have been observing a problem at the art center with some of our
glaze pieces. This is student work, I haven't been able to determine
any one factor that may be causing the problem. I seem to be seeing
more cracks showing up in the glaze fire lately. We are firing to cone
6 in skutt 1027's. I'm not sure if it's happening i one kiln more than
the other. The pieces appear sound prior to the firing, but come out of
the glaze cracked. It is apparent by the way the glaze has melted
around the edges of the cracks that the crack separates or happens prior
to the glaze melting. This seems to be happening more since I changed
over to Ron and John's suggested firing schedule for cone 6.
I'm wondering if there is something inherent in the way electric kilns
heat and cool that could be contributing, if it is a silica/cristobalite
issue, the particular clay we are using ( Aardvark Texas White), the
bisque temp. or what. Most of the posts I can't see anything in the way
they are constructed or made that I can point a finger at.
Any ideas?
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Ron Roy on sun 21 jul 02
Hi Earl
I would guess the cracking is happening as the bisque firing cools - at the
quartz inversion. Sometimes these cracks - because they close up as the
rest of the pot goes through the inversion - are difficult to see. As the
ware begins to sinter during the glaze firing - and soften - these cracks
open up.
If the glaze has melted into the cracks it means the cracks opened on the
way up - so you can't blame slow cooling.
My first question would be - what cone are you bisqing to? What kind of
body is it - what percent of free silica is being mixing into the body.
Is the ware thin on the rim and heavy in the foot - are the cracking pots
from the bottom or the top of the firing - or the sides? Is there any kind
of pattern - like plates and bowls rather than cups and bottles?
There has been some talk of replacement of Ione grog with other grog - some
of which has some cristobalite associated - better ask Ardvark what kind of
grog they are using now?
Bisque will ring if it's not cracked by the way - see if you can find some
with cracks - firing it higher can make it strong enough to get through the
inversions.
RR
>I have been observing a problem at the art center with some of our
>glaze pieces. This is student work, I haven't been able to determine
>any one factor that may be causing the problem. I seem to be seeing
>more cracks showing up in the glaze fire lately. We are firing to cone
>6 in skutt 1027's. I'm not sure if it's happening i one kiln more than
>the other. The pieces appear sound prior to the firing, but come out of
>the glaze cracked. It is apparent by the way the glaze has melted
>around the edges of the cracks that the crack separates or happens prior
>to the glaze melting. This seems to be happening more since I changed
>over to Ron and John's suggested firing schedule for cone 6.
>
>I'm wondering if there is something inherent in the way electric kilns
>heat and cool that could be contributing, if it is a silica/cristobalite
>issue, the particular clay we are using ( Aardvark Texas White), the
>bisque temp. or what. Most of the posts I can't see anything in the way
>they are constructed or made that I can point a finger at.
>
>Any ideas?
>
>
>--
>Earl Brunner
>http://coyote.accessnv.com/bruec
>mailto:bruec@anv.net
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
John Christie on mon 22 jul 02
Earl Brunner wrote:
>I have been observing a problem at the art center with some of our
>glaze pieces. This is student work, I haven't been able to determine
>any one factor that may be causing the problem. I seem to be seeing
>more cracks showing up in the glaze fire lately. We are firing to cone
>6 in skutt 1027's. I'm not sure if it's happening i one kiln more than
>the other. The pieces appear sound prior to the firing, but come out of
>the glaze cracked. It is apparent by the way the glaze has melted
>around the edges of the cracks that the crack separates or happens prior
>to the glaze melting.
I agree with Ron Roy that the cracks were probably there at the end of the
bisque firing though hard to spot. Usually this type of hairline crack is
easier to see after glaze dipping when they will appear as tiny lines of
thicker glaze (the crack has slightly more absorbency than the surrounding
clay). As Ron points out, these can be caused by underfired bisque -
especially if there has been equipment failure resulting in a bisque kiln
failing to reach temperature - perhaps only locally if only one element has
failed in an electric kiln.
Other causes of these cracks are:
1. Speed-drying in hot sun or on a kiln. Especially where lidded pots are
dried with their lids on or vessels dried upside down. Vapour from drying
clay condenses on dry clay and causes cracks.
2. Similarly, bisque firing damp ware can have the same result - dry pots
can be cracked by vapour from other pots. Especially where pots are fired
in stacks.
3. Pots that have been frozen at the leather-hard stage may appear sound
but may develop very similar cracks (usually cobweb shaped) after bisque
firing.
4. Hairline cracks (but not cobweb shaped) may result from careless
handling of dry pots (or dunting).
John Christie.
www.blackhillspottery.co.uk
Fredrick Paget on mon 24 jul 06
Thinking about S cracks - I have never really bought the
"compressing" argument.
I believe and my theory is that the S cracks originate from lapped
over places in the clay mass created as the clay is wedged, Look at
the clay before you slam it down on the bat . Does it have visible
lines where the clay has been layered over another part of the clay
mass? these are weak points and it is hard to eliminate them by
"Compressing" from the top side.select a part of the clay ball or
cone that is free or these weak points as the future bottom of your
piece.
Then the next thing that causes cracks is uneven drying where the
outside of a piece drys before the center. Now the outside is
shrunken a little and the clay is hard while the center is still wet.
As the center drys it shrinks a bit and the outside being hard won't
give, so the center part cracks as it shrinks. This kind of a crack
is different from the previous S crack, being long and straighter or
curved around the pot edge. Io avoid this keep the pot covered in
plastic.
Sometimes I even cut a hole in the center of the plastic so the
center bottom is exposed so it drys first. As it shrinks it can pull
in the still plastic clay around the edges.
I have been working with some new cone 5 clays that are prone to
cracks. It really emphasizes these points to you.
--
From Fred Paget,
Marin County, CA, USA
fredrick@well.com
Charter Member Potters Council
Heidi Fahrenbacher on mon 24 jul 06
This past week I went to the Ann Arbor Art Fair and I was looking at lots of
pots. I noticed on the bottom of several artists' pieces that there were
small "S" cracks on the underside of the piece, but the cracks didn't
pentrate the interior.
I have this same problem with my work. The cracks don't appear until after
the piece has been fired. What's going on? Plus is it good to sell these
pieces? I've read that cracks on fucntional work can be a nice home for
bacteria. I've been selling all my pots with tiny cracks as seconds.
Does anyone have experience with these type of cracks? Please help!
Thanks,
Heidi
Fahrenbacher
Nancy Braches on mon 24 jul 06
Heidi
I am in no way an expert but I learned about compressing the bottoms both when you throw and when trimming. S cracks were in some of my bowls/plates when I first started throwing and when my instructor told me about compressing and how important it is, it took care of my problem.
I very rarely get S cracks in my pieces. But I probably compress more than necessary :)
Nancy
Heidi Fahrenbacher wrote: This past week I went to the Ann Arbor Art Fair and I was looking at lots of
pots. I noticed on the bottom of several artists' pieces that there were
small "S" cracks on the underside of the piece, but the cracks didn't
pentrate the interior.
I have this same problem with my work. The cracks don't appear until after
the piece has been fired. What's going on? Plus is it good to sell these
pieces? I've read that cracks on fucntional work can be a nice home for
bacteria. I've been selling all my pots with tiny cracks as seconds.
Does anyone have experience with these type of cracks? Please help!
Thanks,
Heidi
Fahrenbacher
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Nancy Braches on mon 24 jul 06
Heidi
I forgot to mention that, at one point, I used the nice thick bats from bailey supply and left my pieces to dry without wiring them off first and I had cracking problems. Now I wire them once and let them sit, has saved me from having cracks again.
Nancy
Hilltop Pottery
Heidi Fahrenbacher wrote: This past week I went to the Ann Arbor Art Fair and I was looking at lots of
pots. I noticed on the bottom of several artists' pieces that there were
small "S" cracks on the underside of the piece, but the cracks didn't
pentrate the interior.
I have this same problem with my work. The cracks don't appear until after
the piece has been fired. What's going on? Plus is it good to sell these
pieces? I've read that cracks on fucntional work can be a nice home for
bacteria. I've been selling all my pots with tiny cracks as seconds.
Does anyone have experience with these type of cracks? Please help!
Thanks,
Heidi
Fahrenbacher
______________________________________________________________________________
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William & Susan Schran User on mon 24 jul 06
On 7/24/06 9:11 AM, "Heidi Fahrenbacher" wrote:
> I have this same problem with my work. The cracks don't appear until after
> the piece has been fired. What's going on? Plus is it good to sell these
> pieces?
"S" cracks generally are a result of one or any combination of: clay body,
insufficient compression or too great a change in thickness.
Some clay bodies, often bodies composed of primarily fine particle clays can
be more prone to this cracking issue. Clay bodies will perform better and
less subject to many problems if they are composed of clays of various
particle sizes.
If after trimming the bottom of the pot is not compressed well, this can
lead to cracking. This is especially true of work thrown off a mound.
If a pot is trimmed, or not trimmed, and the thickness of the clay at the
center of the bottom is very thin and the thickness at the edge of the
bottom, where it turns or transitions into the wall, is quite a bit thicker,
this can lead to cracking issues.
I don't sell anything with cracks.
I don't sell seconds, my name is on that pot.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
John Rodgers on mon 24 jul 06
I very rarely get cracks - "S" or otherwise - in my pot bottoms. Proper
compressing is the key. And to, I use plaster bats. I never wire cut a
pot from the bat. The pots will "self-release" when they are good and
ready, and the bottom will be very smooth with no trimming required.
There is often talk about getting plaster chips into the clay .... but
it never has happened to me and I have been using the plaster bats for
some 10 plus years now. I don't beat up my bats. The only drawback to
the plaster bat for me is they are somewhat heavy, but they do release a
pot so easy and usually within a couple of hours or so of being thrown.!
John Rodgers
Chelsea, AL
Heidi Fahrenbacher wrote:
> This past week I went to the Ann Arbor Art Fair and I was looking at lots of
> pots. I noticed on the bottom of several artists' pieces that there were
> small "S" cracks on the underside of the piece, but the cracks didn't
> pentrate the interior.
>
> I have this same problem with my work. The cracks don't appear until after
> the piece has been fired. What's going on? Plus is it good to sell these
> pieces? I've read that cracks on fucntional work can be a nice home for
> bacteria. I've been selling all my pots with tiny cracks as seconds.
>
> Does anyone have experience with these type of cracks? Please help!
>
> Thanks,
> Heidi
> Fahrenbacher
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
>
Nancy Braches on tue 25 jul 06
Compressing as well as "other" factors all can lead to S cracks. I don't think one is the perfect answer but each person has to see what is their own problem. From experience I personally have found that if I compress, no problem. If I don't....S cracks everywhere. Wedging and drying doesn't seem to be my problem. So the best advice for anyone with the problem is to look at all areas of their pot making...wedging, compressing AND drying. Changing each one (or all) and see if it fixes the problem. I know from experience, when I dried my piece inappropriately, even though I compressed well, the cracks came back. So it became apparent, it is a factor of all things and different for each potter.
Fredrick Paget wrote: Thinking about S cracks - I have never really bought the
"compressing" argument.
I believe and my theory is that the S cracks originate from lapped
over places in the clay mass created as the clay is wedged, Look at
the clay before you slam it down on the bat . Does it have visible
lines where the clay has been layered over another part of the clay
mass? these are weak points and it is hard to eliminate them by
"Compressing" from the top side.select a part of the clay ball or
cone that is free or these weak points as the future bottom of your
piece.
Then the next thing that causes cracks is uneven drying where the
outside of a piece drys before the center. Now the outside is
shrunken a little and the clay is hard while the center is still wet.
As the center drys it shrinks a bit and the outside being hard won't
give, so the center part cracks as it shrinks. This kind of a crack
is different from the previous S crack, being long and straighter or
curved around the pot edge. Io avoid this keep the pot covered in
plastic.
Sometimes I even cut a hole in the center of the plastic so the
center bottom is exposed so it drys first. As it shrinks it can pull
in the still plastic clay around the edges.
I have been working with some new cone 5 clays that are prone to
cracks. It really emphasizes these points to you.
--
From Fred Paget,
Marin County, CA, USA
fredrick@well.com
Charter Member Potters Council
______________________________________________________________________________
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Dorie Mickelson on tue 25 jul 06
Heidi,
I've always been taught that four things can potentially lead to cracks in
the bottom of pots -- (1) the bottoms being too thick; (2) not compressing
the bottoms enough; (3) leaving water sitting in the bottom of the pot
during or after throwing; and/or (4) uneven drying of pots. Address these
four three issues and you should not have any more cracks!
I would not recommend selling any pots with cracks on the bottoms whether
they penetrate the interior or not. Not even as seconds. In my opinion,
they are not structurally sound, and as such, are defective.
I do still occasionally keep some defective pots for my own personal use in
my studio (to hold brushes, etc.), but more and more, I have learned to just
hammer the bad pots and to make room for better ones!
Best,
Dorie Mickelson in Ann Arbor, Michigan
www.FreeSpiritCreations.com
SNIP < From: Heidi Fahrenbacher, Subject: cracks; This past week I went to
the Ann Arbor Art Fair and I was looking at lots of pots. I noticed on the
bottom of several artists' pieces that there were small "S" cracks on the
underside of the piece, but the cracks didn't penetrate the interior. I
have this same problem with my work. The cracks don't appear until after the
piece has been fired. What's going on? Plus is it good to sell these pieces?
I've read that cracks on functional work can be a nice home for bacteria.
I've been selling all my pots with tiny cracks as seconds. Does anyone have
experience with these type of cracks? Please help!>
Norman Aufrichtig on tue 25 jul 06
hi fred,
not to discount what you said, am careful how i use the clay from the
pugmill, but if you want to test the compression argument i have a
suggestion. throw some forms off the hump but do not compress the bottom,
throw some more but compress the bottom use a rib to do this, they should
all have the same thickness bottom. don't trim the bottom, as this does
compress the bottom. i think this will show the value of compressing .
drying is somewhat important but if a piece is well thrown it can be dried
pretty fast. i live in the dry southwest use b mix and dry my clay very
fast, very seldom do i have a problem with cracking.
norman a
----- Original Message -----
From: "Fredrick Paget"
To:
Sent: Monday, July 24, 2006 10:20 PM
Subject: Re: [CLAYART] cracks
> Thinking about S cracks - I have never really bought the
> "compressing" argument.
>
> I believe and my theory is that the S cracks originate from lapped
> over places in the clay mass created as the clay is wedged, Look at
> the clay before you slam it down on the bat . Does it have visible
> lines where the clay has been layered over another part of the clay
> mass? these are weak points and it is hard to eliminate them by
> "Compressing" from the top side.select a part of the clay ball or
> cone that is free or these weak points as the future bottom of your
> piece.
>
> Then the next thing that causes cracks is uneven drying where the
> outside of a piece drys before the center. Now the outside is
> shrunken a little and the clay is hard while the center is still wet.
> As the center drys it shrinks a bit and the outside being hard won't
> give, so the center part cracks as it shrinks. This kind of a crack
> is different from the previous S crack, being long and straighter or
> curved around the pot edge. Io avoid this keep the pot covered in
> plastic.
>
> Sometimes I even cut a hole in the center of the plastic so the
> center bottom is exposed so it drys first. As it shrinks it can pull
> in the still plastic clay around the edges.
>
> I have been working with some new cone 5 clays that are prone to
> cracks. It really emphasizes these points to you.
>
> --
> From Fred Paget,
> Marin County, CA, USA
> fredrick@well.com
>
> Charter Member Potters Council
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
>
>
> --
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>
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Fredrick Paget on tue 25 jul 06
>hi fred,
>not to discount what you said, am careful how i use the clay from the
>pugmill, but if you want to test the compression argument i have a
>suggestion. throw some forms off the hump but do not compress the bottom,
>throw some more but compress the bottom use a rib to do this, they should
>all have the same thickness bottom. don't trim the bottom, as this does
>compress the bottom. ...etc
I am not saying that compressing is bad. I believe that it is a step
toward smearing the clay in those shear planes that you get as the
clay is wedged or from the twisting the clay gets in off the hump
throwing, I just say try not to put the laps or shear planes on the
bottom if you can avoid it. Clay properties are a big factor. I like
to work with the rattiest most awful clay I can get to see if I can
beat it into submission. You get to the point where you can do that
then good clay is sooo easy!
--
From Fred Paget,
Marin County, CA, USA
fredrick@well.com
Charter Member Potters Council
Ivor and Olive Lewis on wed 26 jul 06
Dear Fredrick Paget,=20
You may be on the right track there but consider first that Clay, at the =
force which exerted by a fingertip or a laid over Rib will never be =
compressed.
When these tools are moved over the base on the inside of a cylinder or =
the face of a plate, fluid movement takes place. This is a fundamental =
property of Plastic Materials and clay/water, being plastic, flows. If =
the motion of the tool is dominantly from the periphery to the centre, =
clay is moved inward to the centre. When it gets to the axis of rotation =
pressure from the finger or the rib forces it to descend to the =
wheelhead or bat surface. It then reverses its direction of flow and =
moves back to the circumference again.
This process reduces floc size through Shear and also attenuates the =
dimensions of flocs, stretching them and thinning them. IF there is =
insufficient water in the plastic will clay fracture, When these =
fractures, which are sub-microscopic in width, do not heal they remain =
as faults. When there is sufficient water in the clay/water mixture it =
re-adheres to itself, eliminating the fault. If the clay does not have =
sufficient water crack faces separate as clay shrinks. Often they are so =
small may not reveal themselves until the work is fired. This was =
described in Pottery Making Illustrated some years ago.
Best regards
Ivor Lewis.
Redhill,
South Australia.
Alisha Clarke on wed 26 jul 06
A couple of months ago I visited a large studio/retail space that I really
respected that includes work from about eight potters. It's a beautiful
space in a beautiful setting and I have enjoyed visiting there whenever I'm
in the area (I won't give the name or location). This last time I was there,
however, they had two potters working on wheels throwing off the mound. One
was throwing small bud vases, but the other was doing some nice large mugs.
I was curious to see how he did it, since I've never mastered throwing off
the mound, primarily because I could never figure out how to compress the
bottoms sufficiently to avoid S-cracks. I didn't want to interrupt his work,
so I went and looked at some of the finished mugs for sale. What do ya know
... they all had S-cracks going all the way through and they were simply
filled with some sort of sealer (I believe silicone). And, they were being
sold for FULL PRICE -- $20 a mug. I was tempted to say something to them at
the time, but decided it wasn't my business and left, but it has been
bothering me ever since then. I really think it was unethical to be selling
them that way, without marking them as seconds. I'm sure many clients will
not look carefully at the bottoms before buying them. Who knows what toxins
might be released into a hot cup of coffee from the sealant, not to mention
the shoddy craftsmanship.
I know there are other potters there and hopefully they would not do the
same, but the fact that the studio would be selling them that way really
bothered me. I lost a lot of respect for them. I guess the message is that
you're just hurting yourself if you sell goods with known flaws, unless you
mark and sell them as seconds.
Leesh
~~~~~~~~~~~~~~~~~~~~~~~~~
Alisha Clarke
www.alishaclarke.com
On 7/25/06, Dorie Mickelson wrote:
>
> Heidi,
>
> I've always been taught that four things can potentially lead to cracks in
> the bottom of pots -- (1) the bottoms being too thick; (2) not
> compressing
> the bottoms enough; (3) leaving water sitting in the bottom of the pot
> during or after throwing; and/or (4) uneven drying of pots. Address these
> four three issues and you should not have any more cracks!
>
> I would not recommend selling any pots with cracks on the bottoms whether
> they penetrate the interior or not. Not even as seconds. In my opinion,
> they are not structurally sound, and as such, are defective.
>
> I do still occasionally keep some defective pots for my own personal use
> in
> my studio (to hold brushes, etc.), but more and more, I have learned to
> just
> hammer the bad pots and to make room for better ones!
>
> Best,
>
> Dorie Mickelson in Ann Arbor, Michigan
>
> www.FreeSpiritCreations.com
>
>
>
> SNIP < From: Heidi Fahrenbacher, Subject: cracks; This past week I went to
> the Ann Arbor Art Fair and I was looking at lots of pots. I noticed on the
> bottom of several artists' pieces that there were small "S" cracks on the
> underside of the piece, but the cracks didn't penetrate the interior. I
> have this same problem with my work. The cracks don't appear until after
> the
> piece has been fired. What's going on? Plus is it good to sell these
> pieces?
> I've read that cracks on functional work can be a nice home for bacteria.
> I've been selling all my pots with tiny cracks as seconds. Does anyone
> have
> experience with these type of cracks? Please help!>
>
>
>
--
~~~~~~~~~~~~~~~~~~~~~~~~~
Alisha Clarke
www.alishaclarke.com
Ivor and Olive Lewis on thu 27 jul 06
Dear Alisha Clarke,
Since the techniques you discuss have been well documented by other =
Clayart members, perhaps you might like to enlarge on your description.
Knowing what you do about the process you were observing, did you notice =
if these workers were doing the things you might expect them to do to =
ameliorate the development of flaws as bad as those you saw in their =
finished work ? ?
I support you view that work as badly flawed as this should be treated =
as scrap.=20
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on fri 28 jul 06
Hi Alisha,
You hurt all potters when you sell flawed work - I think we owe it to each
other to at least say something to somebody when we see obvious faults.
One of the students in my class this week saw a very unstable glaze being
used as a liner glaze in pots in a gallery where she sells her work - I
think the gallery owner should be told what the possible problems will be.
RR
>A couple of months ago I visited a large studio/retail space that I really
>respected that includes work from about eight potters. It's a beautiful
>space in a beautiful setting and I have enjoyed visiting there whenever I'm
>in the area (I won't give the name or location). This last time I was there,
>however, they had two potters working on wheels throwing off the mound. One
>was throwing small bud vases, but the other was doing some nice large mugs.
>I was curious to see how he did it, since I've never mastered throwing off
>the mound, primarily because I could never figure out how to compress the
>bottoms sufficiently to avoid S-cracks. I didn't want to interrupt his work,
>so I went and looked at some of the finished mugs for sale. What do ya know
>... they all had S-cracks going all the way through and they were simply
>filled with some sort of sealer (I believe silicone). And, they were being
>sold for FULL PRICE -- $20 a mug. I was tempted to say something to them at
>the time, but decided it wasn't my business and left, but it has been
>bothering me ever since then. I really think it was unethical to be selling
>them that way, without marking them as seconds. I'm sure many clients will
>not look carefully at the bottoms before buying them. Who knows what toxins
>might be released into a hot cup of coffee from the sealant, not to mention
>the shoddy craftsmanship.
>
>I know there are other potters there and hopefully they would not do the
>same, but the fact that the studio would be selling them that way really
>bothered me. I lost a lot of respect for them. I guess the message is that
>you're just hurting yourself if you sell goods with known flaws, unless you
>mark and sell them as seconds.
>Leesh
>
>~~~~~~~~~~~~~~~~~~~~~~~~~
>Alisha Clarke
>www.alishaclarke.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Nancy Braches on sat 29 jul 06
RR
My students look at me in shock when I throw a piece is in the reclaim bucket. Yesterday I threw 4 mugs into it. I forgot to cover them and in this heat the handles dried faster than the mug and started to pull away.
I try to explain safety and pride in work is the most important and we each have our own level of it and when I first started throwing I would have done anything to save those mugs, but now, it's easier for me just to throw 'em all over again.
Nancy
Ron Roy wrote: Hi Alisha,
You hurt all potters when you sell flawed work - I think we owe it to each
other to at least say something to somebody when we see obvious faults.
One of the students in my class this week saw a very unstable glaze being
used as a liner glaze in pots in a gallery where she sells her work - I
think the gallery owner should be told what the possible problems will be.
RR
>A couple of months ago I visited a large studio/retail space that I really
>respected that includes work from about eight potters. It's a beautiful
>space in a beautiful setting and I have enjoyed visiting there whenever I'm
>in the area (I won't give the name or location). This last time I was there,
>however, they had two potters working on wheels throwing off the mound. One
>was throwing small bud vases, but the other was doing some nice large mugs.
>I was curious to see how he did it, since I've never mastered throwing off
>the mound, primarily because I could never figure out how to compress the
>bottoms sufficiently to avoid S-cracks. I didn't want to interrupt his work,
>so I went and looked at some of the finished mugs for sale. What do ya know
>... they all had S-cracks going all the way through and they were simply
>filled with some sort of sealer (I believe silicone). And, they were being
>sold for FULL PRICE -- $20 a mug. I was tempted to say something to them at
>the time, but decided it wasn't my business and left, but it has been
>bothering me ever since then. I really think it was unethical to be selling
>them that way, without marking them as seconds. I'm sure many clients will
>not look carefully at the bottoms before buying them. Who knows what toxins
>might be released into a hot cup of coffee from the sealant, not to mention
>the shoddy craftsmanship.
>
>I know there are other potters there and hopefully they would not do the
>same, but the fact that the studio would be selling them that way really
>bothered me. I lost a lot of respect for them. I guess the message is that
>you're just hurting yourself if you sell goods with known flaws, unless you
>mark and sell them as seconds.
>Leesh
>
>~~~~~~~~~~~~~~~~~~~~~~~~~
>Alisha Clarke
>www.alishaclarke.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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Alisha Clarke on sat 29 jul 06
Hi Ivor,
I didn't observe the whole process of the production (wedging, coning, etc.)
to be certain of why they were getting the s-cracks, but I was curious
because of the problem I've had with s-cracks when throwing off the hump. I
was focusing on whether or not he was doing anything in the throwing process
to compress the bottoms, and I didn't notice it. I think it was Bonnie who
mentioned about coning the clay to avoid cracks, but I wasn't watching for
that at the time.
I'll have to look at the archives for information about throwing off the
hump. It's a weakness for me, but I want to master it if I can.
Alisha
On 7/27/06, Ivor and Olive Lewis wrote:
>
> Dear Alisha Clarke,
>
> Since the techniques you discuss have been well documented by other
> Clayart members, perhaps you might like to enlarge on your description.
>
> Knowing what you do about the process you were observing, did you notice
> if these workers were doing the things you might expect them to do to
> ameliorate the development of flaws as bad as those you saw in their
> finished work ? ?
>
> I support you view that work as badly flawed as this should be treated as
> scrap.
>
> Best regards,
>
> Ivor Lewis.
> Redhill,
> South Australia.
>
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
--
~~~~~~~~~~~~~~~~~~~~~~~~~
Alisha Clarke
www.alishaclarke.com
Alisha Clarke on sat 29 jul 06
Ron,
That's an excellent point. It has been hounding me ever since I saw it. I
think the thing that bothers me, is that it wasn't just a matter of selling
flawed work, but of intentionally trying to cover it up in a way that could
be unhealthy.
I think I may write to the gallery and express my concerns.
Alisha
On 7/29/06, Ron Roy wrote:
>
> Hi Alisha,
>
> You hurt all potters when you sell flawed work - I think we owe it to each
> other to at least say something to somebody when we see obvious faults.
>
> One of the students in my class this week saw a very unstable glaze being
> used as a liner glaze in pots in a gallery where she sells her work - I
> think the gallery owner should be told what the possible problems will
> be.
>
> RR
>
>
>
> >A couple of months ago I visited a large studio/retail space that I
> really
> >respected that includes work from about eight potters. It's a beautiful
> >space in a beautiful setting and I have enjoyed visiting there whenever
> I'm
> >in the area (I won't give the name or location). This last time I was
> there,
> >however, they had two potters working on wheels throwing off the mound.
> One
> >was throwing small bud vases, but the other was doing some nice large
> mugs.
> >I was curious to see how he did it, since I've never mastered throwing
> off
> >the mound, primarily because I could never figure out how to compress the
> >bottoms sufficiently to avoid S-cracks. I didn't want to interrupt his
> work,
> >so I went and looked at some of the finished mugs for sale. What do ya
> know
> >... they all had S-cracks going all the way through and they were simply
> >filled with some sort of sealer (I believe silicone). And, they were
> being
> >sold for FULL PRICE -- $20 a mug. I was tempted to say something to them
> at
> >the time, but decided it wasn't my business and left, but it has been
> >bothering me ever since then. I really think it was unethical to be
> selling
> >them that way, without marking them as seconds. I'm sure many clients
> will
> >not look carefully at the bottoms before buying them. Who knows what
> toxins
> >might be released into a hot cup of coffee from the sealant, not to
> mention
> >the shoddy craftsmanship.
> >
> >I know there are other potters there and hopefully they would not do the
> >same, but the fact that the studio would be selling them that way really
> >bothered me. I lost a lot of respect for them. I guess the message is
> that
> >you're just hurting yourself if you sell goods with known flaws, unless
> you
> >mark and sell them as seconds.
> >Leesh
> >
> >~~~~~~~~~~~~~~~~~~~~~~~~~
> >Alisha Clarke
> >www.alishaclarke.com
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
>
>
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--
~~~~~~~~~~~~~~~~~~~~~~~~~
Alisha Clarke
www.alishaclarke.com
Jennifer Boyer on tue 1 aug 06
Try drying your hump-thrown pieces on a layer of sheetrock over your
ware board. It will speed up the drying of the bottom of the pot.
Some clays are more prone to s cracking than others. Mine requires
this kind of help!
Jennifer
On Jul 29, 2006, at 10:56 AM, Alisha Clarke wrote:
> Hi Ivor,
> I didn't observe the whole process of the production (wedging,
> coning, etc.)
> to be certain of why they were getting the s-cracks, but I was curious
> because of the problem I've had with s-cracks when throwing off the
> hump. I
> was focusing on whether or not he was doing anything in the
> throwing process
> to compress the bottoms, and I didn't notice it. I think it was
> Bonnie who
> mentioned about coning the clay to avoid cracks, but I wasn't
> watching for
> that at the time.
>
> I'll have to look at the archives for information about throwing
> off the
> hump. It's a weakness for me, but I want to master it if I can.
> Alisha
>
*****************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
*****************************
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