Bryan on sun 25 feb 07
Hi All
I have been carving tile, painting slip on while leather hard, and then
scraping off the excess. At first the tile would occasionally crack
when I painted on the slip. In order to correct this I added .75%
paper. Then the tile started getting some 1" to 3" surface cracks where
the slip had been.
I am trying an increase in paper content to 1.25%.
The slip is not deflocculated. I have had other problems with
deflocculated slip.
The body is a cone 6 porcelain that doesn't have molochite.
Any ideas?
Bryan Johnson
Vince Pitelka on mon 26 feb 07
Bryan,
Your comment that the cracks were in the clay rather than in the slip leads
me to believe that perhaps you are carving too deeply. Certainly the most
famous historical mishima work is Korean Koryo Dynasty slip-inlaid celedons.
I think that much of the secret of success in that work was that the carving
was extremely shallow, so that there was less slip to shrink, and the effect
on the claybody was minimal. The down side is that you have to be extremely
careful in scraping the surface so that you don't scrape right through the
inlay. But if you are serious about this, then you are no doubt getting
very sensitive to the thickness of the slip as you are scraping.
I have done a great deal of mishima in both impressed and carved patterns on
various stoneware claybodies using porcelain slip, and have had very little
trouble with cracks along the slip lines. I've always kept the inlays very
shallow.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Lee Love on mon 26 feb 07
On 2/26/07, Bryan wrote:
> I am trying an increase in paper content to 1.25%.
> The slip is not deflocculated. I have had other problems with
> deflocculated slip.
> The body is a cone 6 porcelain that doesn't have molochite.
What is your slip made of?
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Craig Martell on mon 26 feb 07
Hello again Bryan:
If you carve the tile at the leatherhard state and then apply a wet slip
perhaps it would help if you rewet the tile after carving. You might give
the tile a light spray of water. You could then apply the slip and maybe
adding some moisture to the tile would lessen the shrinkage/drying
stresses. Just a thought.
This reminds me of the problems that single fire potters have when raw
glazing. If you glaze at leatherhard, and the piece isn't really evenly
leatherhard, cracks appear after glazing. So many people have chosen to
glaze when the pot is in a pre-leatherhard state, or bone dry.
regards, Craig Martell Hopewell, Oregon
Bryan on mon 26 feb 07
Lee Love wrote:
> On 2/26/07, Bryan wrote:
>
>> I am trying an increase in paper content to 1.25%.
>> The slip is not deflocculated. I have had other problems with
>> deflocculated slip.
>> The body is a cone 6 porcelain that doesn't have molochite.
>
> What is your slip made of?
The same clay body.
Bryan Johnson
Ben Shelton on mon 26 feb 07
I would take another look at deflocculating the slip. It will allow a lower
water content and yet maintain fluidity. That along with a wetter tile may
aleviate the cracking problem.
What types of problems have you had with deffloculated slip in the past?
Ben
Craig Martell on mon 26 feb 07
Hello Bryan:
I think that you said you apply the slip at the leatherhard state. You
might try applying it right away when the clay has more water and hasn't
gone thru much shrinkage. The difference beween a very fluid slip and
leather hard clay may be significant in terms of shrinkage. If this
doesn't work you could calcine some of the body and do a blend of raw and
calcined slip to cut the slip shrinkage somewhat. You can also use darvan
or some other deflocc. additive which would lower the water content of the
slip.
regards, Craig Martell Hopewell, Oregon
Bryan Johnson on mon 26 feb 07
Craig Martell wrote:
> Hello Bryan:
>
> I think that you said you apply the slip at the leatherhard state. You
> might try applying it right away when the clay has more water and hasn't
> gone thru much shrinkage. The difference beween a very fluid slip and
> leather hard clay may be significant in terms of shrinkage.
I can't carve the tile until it is leather hard. I can try darvon
again, but last time I ended up with problems with the slip.
I'll try that again.
Deflocculating the slip makes so much sense, but it was causing problems
with the slip.
The problem seems to be that the moisture from the slip is causing the
clay to expand. The expansion in the middle of the tiles caused a cracks
at the edge. As the slip and tile dried the edges pulled back together.
After trying the paper addition the cracks were only under areas slip.
The tile was strong enough to resist the edge cracking, but absorbed
moisture and then cracked during drying where the slip had been.
> If this
> doesn't work you could calcine some of the body and do a blend of raw and
> calcined slip to cut the slip shrinkage somewhat. You can also use
> darvan
> or some other deflocc. additive which would lower the water content of
> the
> slip.
The crack wasn't in the slip, which is what I would expect the calcining
to address.
I think that the quantity of pigment in the black slip is acting as the
non-plastic component.
I do like the idea of decreasing the water content of the slip.
>
> regards, Craig Martell Hopewell, Oregon
Bryan Johnson
Bryan on tue 27 feb 07
Lee Love wrote:
> On 2/28/07, Bryan wrote:
>
>>
>> About the control of slip removal, I have been using a Bison loop
>> tool
>
> This is another possible problem. A loop tool takes too much clay
> off when you scrap because of the curve of the tool. You really
> don't want to cut into the clay body like you do when you are trimming
> a foot. It is better to use a Japanese style kana kept very sharp.
> Mine are so sharp I can shave with them. My favorite tool has a
> curved blade on one end and a flat blade with a curved edge on the
> other. You mostly use the flat blade. Remember, you are just
> cleaning the surface, like cutting off whiskers, not biting into the
> flesh.
Exactly what it does. They come in a wide variety of curves, even
straight ones.
>
> Another little change I learned at Shimaoka's workshop (he was
> recognized as a national living treasure for the specific technique of
> rope impressed inlay), is rather than sharpening the outside edge of
> the kana, as you do for pot trimming, you sharpen the inside edge.
> This is better for scraping and also makes it easier to keep the tool
> sharp, because you can set it on the edge of a table and file the
> inside edge while holding the handle of the tool.
>
I've tried to talk Phil into making me a tool with that edge sharpened.
I am trying the drier approaches first because the slabs are already
leather hard.
Bryan Johnson
Lee Love on tue 27 feb 07
Hi Bryan,
So, the inlay has much less shrinkage than the clay body?
Do you need to put paper in the body too?
Lee in Mashiko
On 2/26/07, Bryan wrote:
> The same clay body.
>
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Lee Love on tue 27 feb 07
So the inlay is cracking because it shrinks more than the body that
has paper in it. That makes total sense.
. If the moisture is from the slip is causing the clay body to
crack, you need to equalize the moisture. Dryer slip and softer
claybody. The body will crack if you apply slip when the body is too
dry. My inlay slip is as thick as possible. The water is skimmed
off the top before I scoop it out of the larger bucket into the
application tub.
If you are inlaying deep impressions it might be better to
use soft clay, rather than slip. Shimaoka does with when inlaying
large circles on pots. You rub the clay into the depressions. Let it
dry a little, then burnish
Also, after you apply the slip, cover the pots and let the
moisture equalize before allowing the slip to dry.
Some of my inlay and hakeme work:
http://claycraft.blogspot.com/
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Lee Love on tue 27 feb 07
On 2/27/07, Bryan Johnson wrote:
> Craig Martell wrote:
> > Hello Bryan:
> >
> > I think that you said you apply the slip at the leatherhard state.
>I can't carve the tile until it is leather hard.
Bryan, this is the key. You have to catch the clay at its
softest leather hard. With Jomon Zogan, if the clay is too hard, we
always use a brush and wet the surface. The good safety feature of
rope impression, is that if the clay is too hard for the inlay, it
will crack from the pressure of the rope.
> The problem seems to be that the moisture from the slip is causing the
> clay to expand. The expansion in the middle of the tiles caused a cracks
> at the edge. As the slip and tile dried the edges pulled back together.
That is why you have to work at the softest leatherhard possible.
If you are having trouble with the carving, try different tools.
I put up some photos of a tsubo I carved fish into. I tried
different tools for the carving and ended up using a blunted sharpened
pencil. There are some cracks in the inlay, but it is impossible to
avoid with unglazed shigaraki clay:
http://mashikopots.blogspot.com/
The difference in color of the different shots is from an
incandescent light I used, trying to get glare off the pot to show the
fish.
The last pot was sold to a good customer who saw it after buying
a tea bowl from me on Esty, because I packed the show card that
featured it with the pots he bought. You can see my Esty online
store here:
http://www.ikiru.etsy.com/
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Bryan on tue 27 feb 07
Ben Shelton wrote:
> I would take another look at deflocculating the slip. It will allow a lower
> water content and yet maintain fluidity. That along with a wetter tile may
> aleviate the cracking problem.
>
> What types of problems have you had with deffloculated slip in the past?
>
> Ben
>
>
The slip started cracking when it was deflocculated.
This time around I am going to try applying slip to a bone dry tile,
1.25% paper fiber content in the body, and as undetermined slip, or slips.
Vince,
About the control of slip removal, I have been using a Bison loop
tool and selectively leaving some slip as shading. _Unfortunately _I
do like lines deeper than a traced pencil line
Bryan
Vince Pitelka on tue 27 feb 07
Bryan wrote:
> About the control of slip removal, I have been using a Bison loop
> tool and selectively leaving some slip as shading. _Unfortunately _I
> do like lines deeper than a traced pencil line
Bryan -
Who said anything about a traced pencil line?? I always use a standard
stainless steel rib, sharpening it occasionally by holding the rib
vertically at 90 degrees to a sharpening stone, with the straight edge
against the stone, giving you a square edge with two sharp cutting edges.
With a sharpened rib, it's easy to remove the clay in very thin passes, so
that you can stop before you cut through the mishima.
If you want to stop the cracking, then do shallow inlays. It's as simple as
that.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Heather Pedersen on wed 28 feb 07
On Tue, 27 Feb 2007 18:47:42 -0600, Bryan wrote:
>This time around I am going to try applying slip to a bone dry tile,
>1.25% paper fiber content in the body, and as undetermined slip, or slips.
Why are you using bone dry tiles with your slip? Everything I've heard
about this technique is that it is best to use a leatherhard tile. I
assume you're trying for something particular that requires a bone dry
tile, or a very thin application of slip? Otherwise that seems a bit like
shooting yourself in the foot.
Regards,
-= Heather Pedersen
Bob Santerre on wed 28 feb 07
Yes, Bryan, I would echo what Craig has mentioned in his last paragraph
(below) ... apply the slip to a bone dry piece. I spray slip onto large
bowls and vases, but ONLY after they are bone dry greenware. I've
tried spraying at the leatherhard stage, but have found that there's a
much greater incidence of cracking at this stage. Even with bone dry
ware I do get an occasional crack, especially on bowl rims, but the
cracking problem is 10 times worse with leatherhard ware. Minimizing
the amount of water in the slip as much as you can (Darvan, calcining)
and applying to bone dry ware will give you the best shot.
Bob
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
Craig Martell wrote:
> Hello again Bryan:
>
> If you carve the tile at the leatherhard state and then apply a wet slip
> perhaps it would help if you rewet the tile after carving. You might
> give
> the tile a light spray of water. You could then apply the slip and maybe
> adding some moisture to the tile would lessen the shrinkage/drying
> stresses. Just a thought.
>
> This reminds me of the problems that single fire potters have when raw
> glazing. If you glaze at leatherhard, and the piece isn't really evenly
> leatherhard, cracks appear after glazing. So many people have chosen to
> glaze when the pot is in a pre-leatherhard state, or bone dry.
>
> regards, Craig Martell Hopewell, Oregon
>
> ______________________________________________________________________________
>
> 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.
>
>
>
Lee Love on wed 28 feb 07
On 2/28/07, Bryan wrote:
>
> About the control of slip removal, I have been using a Bison loop
> tool
This is another possible problem. A loop tool takes too much clay
off when you scrap because of the curve of the tool. You really
don't want to cut into the clay body like you do when you are trimming
a foot. It is better to use a Japanese style kana kept very sharp.
Mine are so sharp I can shave with them. My favorite tool has a
curved blade on one end and a flat blade with a curved edge on the
other. You mostly use the flat blade. Remember, you are just
cleaning the surface, like cutting off whiskers, not biting into the
flesh.
Another little change I learned at Shimaoka's workshop (he was
recognized as a national living treasure for the specific technique of
rope impressed inlay), is rather than sharpening the outside edge of
the kana, as you do for pot trimming, you sharpen the inside edge.
This is better for scraping and also makes it easier to keep the tool
sharp, because you can set it on the edge of a table and file the
inside edge while holding the handle of the tool.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Bryan Johnson on wed 28 mar 07
Having read and then trying the easiest to implement suggestion,
applying slip when the tile is past leather hard, I finally have some
results.
There wasn't any cracking during drying, a couple cracked during firing.
I'll probably try deflocculating the slip in a week or so.
Thanks for the suggestions.
Bryan Johnson
Marengo, Wi
| |
|
