LTDeane@aol.com on sun 29 sep 96
Anyone else out there doing colored porcelain inlay work ? I am having a
problem with cracking along the inlay lines in the second firing ( ^5 ) I
am inlaying sometimes 5 layers of colored porcelain into a thin slab of white
( compatiable ) porcelain, to " paint " a picture of sorts. I take lots of
care to compress hard , each layer into the slab, and even finely sand the
dried green piece before I bisque to ^06. The pieces come out of the
bisque just fine with no cracking in sight...........it is only at the higher
temp of ^5 that the cracking along the different lines of the colored clay
appears. It happens both when I apply a clear glaze over or no glaze. All
the clay is compatible as I mix mason stains into the white porcelain for my
colors.........The ONLY thing I can think of is that I must compress even
harder.to mesh the clay better.....but so often when I do this the colored
clay " bleeds " into the white background............Any advice ? Thanks
Laurie in Annapolis
Andrew S Lubow on tue 1 oct 96
Are you using the same body with colorants added?
On Sun, 29 Sep 1996 22:51:31 EDT LTDeane@aol.com writes:
>----------------------------Original
>message----------------------------
>Anyone else out there doing colored porcelain inlay work ? I am having
>a
>problem with cracking along the inlay lines in the second firing ( ^5
>) I
>am inlaying sometimes 5 layers of colored porcelain into a thin slab
>of white
>( compatiable ) porcelain, to " paint " a picture of sorts. I take
>lots of
>care to compress hard , each layer into the slab, and even finely
>sand the
>dried green piece before I bisque to ^06. The pieces come out of
>the
>bisque just fine with no cracking in sight...........it is only at the
>higher
>temp of ^5 that the cracking along the different lines of the colored
>clay
>appears. It happens both when I apply a clear glaze over or no
>glaze. All
>the clay is compatible as I mix mason stains into the white porcelain
>for my
>colors.........The ONLY thing I can think of is that I must compress
>even
>harder.to mesh the clay better.....but so often when I do this the
>colored
>clay " bleeds " into the white background............Any advice ?
>Thanks
> Laurie in Annapolis
>
ZALT@aol.com on thu 3 oct 96
I don't do clay inlay but I suggesst that you try mixing a little frit into
your colour clay. Even though your using the same clay with colour added you
must remember that the pigment will affect the flux in the clay. This may be
just sufficient to cause the separation. Another probable reason is that the
two clays: the white porcelain and the colour pigment clay are at different
stages of dryness when you use them. This will cause one clay to mature to
greenware before the other. In turn there will be a great deal of stress
between the two. You could try to wrap the clay slabs extreamly well with
cleaner bags (plastic) after inlaying the design. Leave the peice as long as
possible so that all humidity balances out between the two clays.
Good Luck
Terry
Zane Dmytruk on thu 3 oct 96
LTDeane@aol.com wrote:
>
> ----------------------------Original message----------------------------
> Anyone else out there doing colored porcelain inlay work ? I am having a
> problem with cracking along the inlay lines in the second firing ( ^5 ) I
> am inlaying sometimes 5 layers of colored porcelain into a thin slab of white
> ( compatiable ) porcelain, to " paint " a picture of sorts. I take lots of
> care to compress hard , each layer into the slab, and even finely sand the
> dried green piece before I bisque to ^06. The pieces come out of the
> bisque just fine with no cracking in sight...........it is only at the higher
> temp of ^5 that the cracking along the different lines of the colored clay
> appears. It happens both when I apply a clear glaze over or no glaze. All
> the clay is compatible as I mix mason stains into the white porcelain for my
> colors.........The ONLY thing I can think of is that I must compress even
> harder.to mesh the clay better.....but so often when I do this the colored
> clay " bleeds " into the white background............Any advice ? Thanks
> Laurie in Annapolis
Hi Laurie,
My suggestions for the inlay problem would be to slightly score the
surface you are applying to and or the underside of the inlayed pieces.
At the same time touch a bit of slur (slightly watered down clay) on top
of your score lines before you inlay. If any of the slur should come to
the surface you may be able to remove it with a metal rib. Slow drying
would also be a must. I have not done inlay work, but I think the
priciple for bonding pieces of clay would be the same.
Bond well!
Janice
David Hewitt on fri 4 oct 96
In message , LTDeane@aol.com writes
>----------------------------Original message----------------------------
>Anyone else out there doing colored porcelain inlay work ? I am having a
>problem with cracking along the inlay lines in the second firing ( ^5 ) I
>am inlaying sometimes 5 layers of colored porcelain into a thin slab of white
>( compatiable ) porcelain, to " paint " a picture of sorts. I take lots of
>care to compress hard , each layer into the slab, and even finely sand the
>dried green piece before I bisque to ^06. The pieces come out of the
>bisque just fine with no cracking in sight...........it is only at the higher
>temp of ^5 that the cracking along the different lines of the colored clay
>appears. It happens both when I apply a clear glaze over or no glaze. All
>the clay is compatible as I mix mason stains into the white porcelain for my
>colors.........The ONLY thing I can think of is that I must compress even
>harder.to mesh the clay better.....but so often when I do this the colored
>clay " bleeds " into the white background............Any advice ? Thanks
> Laurie in Annapolis
>
Hi Laurie,
I can't say I do what you describe so I may not be the best person to
help you, but I see no one else seems to have chipped in. However, I do
work with coloured porcelain clays and have done quite a bit with a
laminage technique.
I suspect that your problem is because the inlayed pieces of clay shrink
more in one direction than another. If you roll out any piece of clay in
one direction only you will cause the platelets of clay to line up in
one direction. If you were to then fire this having carefully measured
the width and length you would find that the shrinkage % would not be
same in each direction. We all know, for example, that when throwing a
dish with a large diameter base it is necessary to press down and
outwards on the base to get all the clay platelets going round with the
pot, otherwise there is a risk of an 'S' crack in the base. If this is a
correct analysis of the cause of the problem, then the only thing I can
think of is to be careful when rolling out the pieces for inlaying, to
roll in all directions.
It would be interesting to hear from anyone who is successfully doing
your kind of inlay work. Hope you manage to get over the problem.
David Hewitt
David Hewitt Pottery Caerleon, Newport, Gwent, UK.
URL http://digitalfire.com/magic/hewitt.htm
JoAnn Axford on sat 5 oct 96
HI Laurie. I've done some colored clay inlay. I was working with Miller
005 white stoneware, fired to ^6. I was making a slip with dry 005, adding
mason stains to the slip, drying it out and wedging up the colored clay. I
found that keeping the applied colored clay the same consistency as the white
slab to be the key to avoiding cracks. Sometimes I wanted the piece I was
applying to stand out more in my design and I would let it dry out a bit
before applying. If you don't want those cracks,keep your whole piece
covered in plastic except for the spot you are working on. Here is the
process I used. 1. roll out large white slab on slab roller...cover with
plastic..2. roll out colored clays into very thin slabs (by hand) cover with
plastic. 3. cut out colored clay pieces and arrange on the large
slab....cover with plastic. 4..hand roll the applied pieces on the slab. 5.
run the whole slab through the slab roller again....The thickness of your
applied pieces will determine the amount of distortion. Just remember to
keep everything covered with plastic unless you are working on it. Hope this
is helpfull. then again...maybe this is what you already do???????
Yours In Clay JoAnn Axford
Anglersnet on sun 6 oct 96
Have you considered the fact that cracking can occur when the colorants
you are adding are affecting the green and fired shrinkage and cause
differential stress between colored and noncolored areas. Most colorants
will have the effect of either fluxing or making the body more refractory,
depenting on the colorant chemistry, body chemistry and your firing
temperature. Some such as Chrome based pigments can really increase the
fusion temperature dramatically and reduce shrinkage. Iron containing
pigments, depending on the other constituents, can have the opposite
effect. Traditionally one would shift the other basic body ingredients
to compensate for the changes brought about by the pigments. (Increase the
spar or like flux for refractory colorants... reduce for fluxing
colorants) You might try testing the white vs colored body samples for
green and fired shringage, possibly boiled absorbtion, and a firing
deformation test with clay bars.
I hope your solution needn't be too complex.
(Excuse me if this has been discussed previously in the thread.)
Bob Jameson
| |
|
