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Sodium Silicate Crackle Pattern Problem


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#1 MichaelP

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Posted 30 December 2013 - 09:28 AM

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



#2 Brian Reed

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Posted 30 December 2013 - 11:33 AM

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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#3 Marcia Selsor

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Posted 30 December 2013 - 01:34 PM

I agree. I like the large deep cracks and only get them when it is drier. Wetter you get finer lines.
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#4 Diane Puckett

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Posted 30 December 2013 - 05:49 PM

I have done this many times but have never used a torch or done anything to dry the clay prior to applying the SS. Is that just for porcelain?
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#5 JBaymore

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Posted 30 December 2013 - 05:58 PM

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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#6 MichaelP

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Posted 30 December 2013 - 10:39 PM

Thank you guys and girls. Back to my wheel.



#7 docweathers

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Posted 31 December 2013 - 12:12 AM

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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#8 MichaelP

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Posted 04 January 2014 - 09:52 PM

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.



#9 JBaymore

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Posted 04 January 2014 - 10:35 PM

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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#10 JBaymore

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Posted 04 January 2014 - 10:36 PM

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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#11 ayjay

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Posted 05 January 2014 - 09:19 AM

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.

 




#12 docweathers

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Posted 05 January 2014 - 02:07 PM

AyJay

 

The name "crackpots" gives me a sense of close brotherhood with them.

 

John

 

20 seconds to 2 minutes gives me some basic parameters to work with.

 

 

Thanks

 

Larry


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#13 MichaelP

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Posted 05 January 2014 - 04:30 PM

 

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.



#14 MichaelP

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Posted 05 January 2014 - 05:22 PM

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?



#15 JBaymore

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Posted 05 January 2014 - 05:51 PM

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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#16 MichaelP

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Posted 05 January 2014 - 06:22 PM

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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