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
Reply to
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
Reply to
Red Deer
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
Reply to
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
Reply to
slgraber
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.
Reply to
dkat
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.
Reply to
googlegroups2sucks
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
Reply to
slgraber
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
Reply to
Eddie Daughton
very true - you need a good groggy clay. i like soldate60 or soldate30 for my larger bowls.
i also found while getting into bigger stuff (i still throw small on the scale of things - generally under 15 pounds) that throwing an UNusually large pile of clay brings out your mistakes. methods that will work with smaller piles can't work with bigger piles. throw the bigger piles for a while & pay attention to what works. when you go back to your smaller amounts you'll see you throw better then before.
see ya
steve
Reply to
slgraber
Either that, or use a bit more clay and leave the bottom half as a thicker support for the walls and trim it off afterwards - is what I have read :-)
Marianne
Reply to
Bubbles
Thanks all for your input - some really interesting reading....Steve those glazes are supurb - I just cant seem to get the running effect that you have achieved (although the glazes at college used to do that) and I really like it. I'll have to experiment a bit more. I'm gonna get back to the wheel and try again - I gotta master this - I'm not one to let something beat me. JM
Reply to
JM

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