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MichaelP

Sodium Silicate Crackle Pattern Problem

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I recently made a batch of pottery using Sodium silicate to get crackled surface. Everything went extremely well.

 

A couple of days ago I decided to make another batch. I throw a piece, dry the porcelain surface a little with propane flame, apply sodium silicate or its mix with a slip, dry the layer with a heat gun and start stretching.

 

This time I only get vertical cracks that quite quickly become a way too deep. No fine cross pattern (spider web) at all. Same porcelain fresh from the box, same sodium silicate and SS/slip mix as before.

 

I tried thin and thick Sodium silicate layers, flamed and raw porcelain surfaces. The results are still exactly the same.

 

What I didn't try yet is leaving the SS crust a bit more moist. Also, this time I throw mugs, so I leave the porcelain walls thinner since I'm not going to expand them much. But even if I wanted, I couldn't expand them more because of the deep vertical cracks that rip the surface apart as soon as I overstretch it a bit.

 

While I was struggling with porcelain, my wife made a few hand built pieces out of stoneware, and didn't have this problem.

 

What do you think can be the cause?

 

Thank you.

 

Mike

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Mike,

Bingo you have it.  You must not completely dry the sodium silicate.  Just leave it a little moist, and use as thin a coat as you can.  I also learned this the hard way, if I dried the SS completely it must have bonded and hardened too much and the crackly was too deep and made long vertical deep grooves.

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I never use a torch or heatgun after applying the sodium silicate.  It is all about the amount of TIME you leave the sil on there before stretching.  I use a watch.  Differnt clay bodies require different amounts of time for a give type of effect.

 

best,

 

.......................john

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1)  is there an official name for this technique?

2) what is the range of times that you let the sodium silicate set on the clay before you begin to stretch?

3) why do people use a torch or heat gun on it if that's not relevant to the outcome?

 

Larry

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1) is there an official name for this technique?

2) what is the range of times that you let the sodium silicate set on the clay before you begin to stretch?

3) why do people use a torch or heat gun on it if that's not relevant to the outcome?

 

Larry

 

 

1.) I've never heard a "name" for it. I can;t even remember where I picked it up....... it has been AGES.

 

2.) On the clay bodies I have use here and in Japan, times vary from maybe 20 seconds.... to 2 minutes. On the SAME claybody, with the SAME application amount, with the SAME thickness walls, (etc.), the 20 second time will give you different results than the 2 minute time. Generally.... from "less" to "more" change in surface.

 

3.) It makes more dramatic cracks........ but makes it less controllable (at least in my experience).

 

best,

 

...........................john

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I continue trying all possible variations, but on porcelain (vs.stoneware) the cracks remain deep and vertical regardless of what I do.

I'm completely lost.

 

Change your BRUSH.  Change your brushing pattern. (bet you use vertical strokes?)

 

best,

 

.......................john

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1)  is there an official name for this technique?

2) what is the range of times that you let the sodium silicate set on the clay before you begin to stretch?

3) why do people use a torch or heat gun on it if that's not relevant to the outcome?

 

Larry

 

1) I just call them Crackpots, that's completely unofficial.

2) I  brush it on, dry with a heat gun or blowlamp and then start stretching straight away.

3) It's the original way I saw someone do it.   I'll try something different next time.

 

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I continue trying all possible variations, but on porcelain (vs.stoneware) the cracks remain deep and vertical regardless of what I do.

I'm completely lost.

 

Change your BRUSH.  Change your brushing pattern. (bet you use vertical strokes?)

 

best,

 

.......................john

No, not vertical. I apply it circularly while the items rotates on the wheel.

 

Come to think about it, I, indeed, used a wide brush last time when everything turned out fine. Let's come back to it and try again. I'll be shocked if it cures the problem. Let's see...

Thanks John.

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Wow! Just wow! John, I cannot believe it! I took a wide brash of the same kind (2" instead of 1"), and it cured the problem completely.

Thank you so very much. I would've never guessed it.

 

Can you turn water into wine?

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No problem.

 

I use different brushes for different effects also.  (Been doing this trick for at LEAST 30 years.)  There are l ots of changes you can get by differences in application methods.  Play with it.

 

I am actually surprised that your horizontal brushwork gave you vertical cracks.  That is unusual, in my experience.  Unless we are cot really "communicationg" as to what we mean by "vertical cracks".  Which is possible.

 

best,

 

........................john

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The vertical cracks were..well.. perpendicular to the circular (horizontal) brush strokes. On some items, I also saw deep horizontal cracks, but they always appeared after formation of the deep vertical ones as I expanded the walls further.

 

I'll certainly keep this hint in my collection of the not-so-obvious solutions and tricks. 30-year experience means something indeed. :)

 

Thank you again John.

 

Mike

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Hello.. hopefully members will still be "listening" to this thread....  ;O)

 

Just recently learned of this "crack pot" technique and started a few attempts. My question refers to using it in hand built ceramics.

I have had decent results by forming a cylindrical slab pot and applying and drying the sodium silicate and pushing the form out from the inside.. makes nice vases. But I have seen some flat slab forms done with this method an can't figure out how they stretch the slab to introduce the cracks.

 

Any hints on who to make "cracked slabs" to use in construction?

 

Thanks

 

Bob

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Bob,

Cracking a flat slab form can be done by rolling out the slab a little thicker than you want it, paint it with your Sodium silicate and then stretch the slab by throwing it diagonally to the table so that when it hits the table it stretches the slab. A couple of throws should do it enough to get your cracking.

 

 

best,

Pres 

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I apply the SS right after throwing so the clay is still wet, then I dry the surface with a hair dryer for 2 minutes. I get a nice spread of cracks that way. I heard someone call it crackle pots so that's the official/unofficial name I tell people.

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I have experimented with SS one time very early in my throwing journey. Not that I have traveled that far into that realm of clay:

 

1st forms

 

I mixed black stain directly into the SS and applied with a brush with the wheel turning slowly. I dried it a bit with a torch, and  then pushed the form out to produce slightly heavier crackles. SS at one time was sold in degrees twaddle 75 and 150, which indicated it's strength as a deflocculant. Now all I see in SS, which I have to assume is full strength. So perhaps cut it 50/50 with water and try using that way for a more muted effect. The SS in this pic was on porcelain on which I just applied clear gloss for a black/ white finish; then I tossed it.   Practice piece.

 

Nerd

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Thank you Pres for the idea of doing this with a slab. I've used this sodium silicate technique (and taught it in classes) for wheel thrown work, and stretched kohiki slip covered slabs for handbuilt work, but never put the two ideas together. In my handbuilding class this morning, my topic for the students was (more) slab work, so I did one of these just to see what would happen. It was awesome! The students were amazed at the instant alligator skin. A whole new body of work just started!

S. Dean likes this

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dick, the addition of a few pressed circles to your slab before stretching it will give you ovals with crackles when you are finished.  small jar openings pressed over a stretched piece of cloth work for the circles.  once you see how easy, the possibilities are unlimited.

 

michael, randy broadnax has a youtube video on doing thie technique you have tried.

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Hello.. hopefully members will still be "listening" to this thread....  ;O)

 

Just recently learned of this "crack pot" technique and started a few attempts. My question refers to using it in hand built ceramics.

I have had decent results by forming a cylindrical slab pot and applying and drying the sodium silicate and pushing the form out from the inside.. makes nice vases. But I have seen some flat slab forms done with this method an can't figure out how they stretch the slab to introduce the cracks.

 

Any hints on who to make "cracked slabs" to use in construction?

 

Thanks

 

Bob

 

Who were the potters? Or link to the work in which you are interested?  Sodium silicate is one way to achieve a crackled surface, but there are others.

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