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hanee

High Grog Core With Grogless Surface Modeling

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I'm wondering if I should expect to encounter any problems in the firing or drying stage if, with the exact same base body, I use a very highly grogged core but use an ungrogged version of the same body for, say, the last eigth to quarter of an inch of the form. I can't think of any plausible reason why it wouldn't work if dried patiently, but being a sculptor, and not a potter, I thought it was worth asking those who know.

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Thanks! I will go ahead and risk it on my next figure, as it would be nice to have the possibility of relying on a high grog formula for strength but still being able to have a more refined surface if needed.

 

I do have a question for my understanding: when people use terra sig aren't they effectively doing the same thing as putting a high-shrinkage clay on top of a low-shrinkage clay? Is it the *thinness* of the second layer what allows it to work? If so, why would a thin layer be any less subject to cracking than a thick layer? I'm not quite understanding why thick vs thin would matter.

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Terra sig is water thin ... It fills in the small low spots to give an overall smoothness. Then people burnish it by rubbing the surface so it gets well meshed with the under layer. It is a low fire process.

 

You could smooth your surface by making a terra sig with your clay body and brushing it on. That way you would get smoothness yet still be able to see the textures of your grog.

 

Why thin layers? The humidity evens out better than one thick layer. Think of painting your living room by applying the thickest coat you can ... The paint would start to slide down the wall because the wall could not absorb the water quick enough. Two coats over two days works 100% better because it has time to even out and dry so it can accept the next layer.

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Could you just use a rib, or some type of burnishing tool to smooth the surface?  I know that might be a bit of an issue with your intricate work, but a possibility.  Chamois work on the wheel, at smoothing, without raising the grog, so it should work on sculptures as well.  They do have potter's sponges out there, that are supposed to give the same smooth surface as a chamois too.

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Chris, I'm working low-fire so I'm wondering if I should expect a higher success rate with a second layer in either case. Thanks for the explanation of terra sig, I know about it, but have never used it as I've never used a glaze process. The way I'm understanding your explanation of the sig is that it's effectively cracked already as its individual particles are filling in between the other clay particles and there are gaps in between, so you're not dealing with an eggshell thin layer that might crack but more of a spatter in which the individual dots moving apart, even at different rates, isn't going to cause any aesthetic issue. --- With the thin layers thing, still a bit confused. I'm not adding wet to dry but clay of the same moisture content to the same moisture content.

 

Benzine, I do smooth the surface in some places and the new clay body I'm using which contains large grog and no small grog smooths quite nicely, when I want it to. The old clay was not as good at that but not terrible either. It's not smoothness that's the goal so much as modeling. It's within the modeling process that the grog gets in the way (though I can work with it fine, it's just it would be a dream to not have to battle with large particles of grog when making a 1/8th inch eyelid). Not looking for a way to get things smoother, per say, but looking for a way to model finer detail with a bit more plasticity/workability while still having the strength I need at the earlier building stage for support of outstretched limbs and the like.

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hanee, why are you using such a heavily grogged clay?  Is it for the added building strength and lessened shrinkage?  The only grogged clay, that I work with, is for Raku purposes, where it serves to minimize the thermal shock.

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Benzine, Haven't really had much in the way of shrinkage problems, it's all for build strength. I haven't the skill to do things like these without grog, though I know Bruno Luccheshi manages to:
 
pond-no1-02-266x400.jpg

 

counter-no3-1-400x400.jpg

 

I'm sure it could work without grog if I tried hard enough, but it's quite difficult for me to manage to work without an armature to begin with, and adding the extra challenge would make the working process all about how to coax the clay into submission instead of letting that fall into the background and putting all my energy into composing and modeling the figure. Also, sculptors work additively as much as possible, so having to have your clay firm up and cut it back is really going to take away from any suppleness of modeling...

 

In something like that child figure above (pond-no1) the head is massive, and even though hollow, it's on a very skinny neck and wants to fall forward. I propped it while working but it's never ideal to do that because it gets in the way of modeling features or noticing asymmetries. If it was not well-grogged clay I would have to prop quite a bit more, might sag and lose the back bend, whole thing might compress as I worked, etc... I like the feel of modeling with grog, too, nice materiality and all, it's just the small details or final surface stuff where it ends up being a big pain sometimes. And I don't like the multi-colored bumpy speckles left behind after firing on more refined work...

 

(Also it seems for good build strength you really need a substantial amount of grog -- the raku clay I used for that figure leaning on a counter was far stronger than the sheffield MGB I used for that child figure; even though the MGB has just the right kind of very-coarse grog that's supposed to be optimal for strength it must have far less total grog than raku clays usually have).

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