Large bowls sagging when throwing

I want to be able to throw large salad bowls, but I have a problem with
sagging just before I finish the throw. Is it better to half throw then
left for a while to dry/firm up before continuing to throw?
Whats the technique for this?
JM

Hi JM,
I've found that when I try to pull too much clay from the bottom, it
seems to cause the sides of the bowl to sag as I refine the sides. I
think you need to leave a large amount of clay at the bottom to support
the bowl as it gets bigger. I know it sounds like a waste of clay.
You have to trim alot later. But you can recycle the trimmings. I
think a large bowl looks best with a large footring anyway. Sometimes,
If my clay is very soft or wet, I will walk away from the wheel and
leave the piece to dry some and come back to it in an hour or so. That
helps to keep it from sagging somewhat.
Good luck,
Sandi

I've found that when I try to pull too much clay from the bottom, it
seems to cause the sides of the bowl to sag as I refine the sides. I
think you need to leave a large amount of clay at the bottom to support
the bowl as it gets bigger. I know it sounds like a waste of clay.
You have to trim alot later. But you can recycle the trimmings. I
think a large bowl looks best with a large footring anyway. Sometimes,
If my clay is very soft or wet, I will walk away from the wheel and
leave the piece to dry some and come back to it in an hour or so. That
helps to keep it from sagging somewhat.
Good luck,
Sandi

Thanks Sandi I'll try that..... I have been trying to save on trimming too
much. Also I have found 'over working' the clay makes it sag, but I've
overcome that and still found that I was getting sagging when throwing
larger items. JM

i find that when throwing bowls or vases, you need to pay attention to
the structure of the pot - or the foundation of the pot. how the walls
stand on the base of the pot.

for vases, i shape from the inside, bottom of the cylinder UP to the
rim. for bowls i shape from the top of the cylinder, stroking DOWN to
the center with my rib, all on the inside of the cylinder.

with bowls, if you shape with the rib on the inside from the bottom UP
& out it's very easy to accidently *kick* the walls off their
foundation. it's also SO very tempting to do this! then the bowl
sags. i do MANY passed from TOP rim down to the bowl center whe
shaping bowls. i never count, but i think it's easily 20 or 30 passes
to fully shape a bowl. and i get them pretty thin.

keep the wall of the bowl in mind. what you really want to do is coax
the walls over. slightly getting the walls to open up more & more each
time. getting there fast breaks this foundation & enables the bowl to
sag or get those "woop-d-doo's" at the transition from wall to bottom.
i shape all the way down to platters this way if i want. i also start
with a wide-ish cylinder, angled outward when i know i want to throw a
bowl.

i strive to have no perceptable distinction between wall & bottom of
bowl.

i apply slight pressure outward at the bowl rim, slowly gaining
pressure to the bottom of the pot. when i'm NOT over the solid pot
foundation, i push outward slowly. when i know i'm over the pot
foundation (base diameter on the wheel head) i press MUCH harder to
smooth that wall-base transition zone.

stroking or shaping the bowl quickly, i feel, puts stresses in the clay
that come out as warping after firing. many smaller inducements to
shaping the bowl usually leave very small warpage to the bowl.

~ hard to explain. no pictures....

see ya

steve

here's some pictures of my finished bowls.

http://www.dataflo.net/~mpurintun/st...ic%20bowls.JPG

see ya

steve

wrote in message
oups.com...

here's some pictures of my finished bowls.

http://www.dataflo.net/~mpurintun/st...ic%20bowls.JPG

see ya

steve

Those are really lovely. Reduction, high fire?

When I throw bowls I pull them more vertical than what they are going to be
and with the walls thicker than what they will end up being. When I have
finished pulling I compress the rim with a chamois and bend it over almost
90degrees to the outside. Starting at the top I take my rib and run it down
the inside repeatedly until I have the shape I want. This is also pulling
the bowl out so that the bent over rim is now gone (that is the side of the
bowl is straight with no bent lip). I trim the bottom with my trimming
stick and then trim very little. How I open the floor actually is what
determines the shape more than anything.

"JM" wrote in message
...
I want to be able to throw large salad bowls, but I have a problem with
sagging just before I finish the throw. Is it better to half throw then
left for a while to dry/firm up before continuing to throw?
Whats the technique for this?
JM

JM wrote:
I want to be able to throw large salad bowls, but I have a problem with
sagging just before I finish the throw.


well, i find that sagging lettuce makes me want to throw large salad
bowls across the dining room. i.e. sagging helps me finish the throw.

dkat - my bowls are all cone 10, cone 11. the base glaze is tenmoku,
with spashings of rutile based glazes *jensen blue* and *jensen red*.
i still use commercial glazes from my supplier Aardvark in santa ana.
nationally thru usa they supply similar glazes to Laguna Clay. ~ same
glaze names. same recipies i guess.

i noticed that these jensen based glazes react REALLY well on top of
iron based glazes such as tenmoku. and they live to get HOT such as
cone11. they run, so i use them inside bowls & on rims of vases.

i discovered over some three years that if the base glaze doesn't fully
dry out before applying the secondary jensen glazes i get a still more
fastenating reaction. ~ that took me a few rainy seasons to see why
sometimes i got this other reaction. i achieve this now from
pre-wetting the bisqueware before applying any glaze.

as far as sagging goes, i'd say throw a few hundred pounds to start to
see the reasons for sagging.

see ya

steve

Could try a body wiv a bit more "tooth".. I find throwing big stuff with
smooth clays is a bit of a no no... so I adds a bit of fine sand (or even a
bit of sanded red clay, gets iron in then too...) Or wedges a bit of a
coarser clay (say Spencroft Magma) into my normal clay (Commercial Clays
APC, (cheapskate.....))
Hugs
Eddie
wrote in message
oups.com...
dkat - my bowls are all cone 10, cone 11. the base glaze is tenmoku,
with spashings of rutile based glazes *jensen blue* and *jensen red*.
i still use commercial glazes from my supplier Aardvark in santa ana.
nationally thru usa they supply similar glazes to Laguna Clay. ~ same
glaze names. same recipies i guess.

i noticed that these jensen based glazes react REALLY well on top of
iron based glazes such as tenmoku. and they live to get HOT such as
cone11. they run, so i use them inside bowls & on rims of vases.

i discovered over some three years that if the base glaze doesn't fully
dry out before applying the secondary jensen glazes i get a still more
fastenating reaction. ~ that took me a few rainy seasons to see why
sometimes i got this other reaction. i achieve this now from
pre-wetting the bisqueware before applying any glaze.

as far as sagging goes, i'd say throw a few hundred pounds to start to
see the reasons for sagging.

see ya

steve