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colekeller

The effects of temperature on slipcasting with darvan

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Hey all, 

I was informed a while back that most commercial slips are deflocculated with Darvan, which can cause adverse effects (warping) on the resulting wares depending on the temperature of the room in which casting occurs. I have found in my testing that this is certainly the case, trying my best to control all other variables within reason only changing the temp of the room. Cold temps certainly seem to increase warping.

What I'm wondering is if anyone has any ideas regarding what the ideal temperature would be for slipcasting with darvan in it. I am trying to minimize warping as much as possible without having to heat my workspace to unnecessarily high temps. I can't seem to find anything about this online and would appreciate any direction greatly! 

Cheers, Cole

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15 minutes ago, colekeller said:

Hey all, 

I was informed a while back that most commercial slips are deflocculated with Darvan, which can cause adverse effects (warping) on the resulting wares depending on the temperature of the room in which casting occurs. I have found in my testing that this is certainly the case, trying my best to control all other variables within reason only changing the temp of the room. Cold temps certainly seem to increase warping.

What I'm wondering is if anyone has any ideas regarding what the ideal temperature would be for slipcasting with darvan in it. I am trying to minimize warping as much as possible without having to heat my workspace to unnecessarily high temps. I can't seem to find anything about this online and would appreciate any direction greatly! 

Cheers, Cole

I remember seeing 62 Fahrenheit, but I don't know if that was ideal or the minimum.

Looking on their specification sheet, their values are taken at 25 Celsius so maybe that is their benchmark.

Edited by liambesaw

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D.D. Button & W.G. Lawrence PHD-Alfred U, "The Effects of Temperature on the Charge on Kaolinte Particles in Water"

@68F the ionic charge responsible for suspension begins to drop: which in turn changes how particles "stack" as they drop out of suspension. The ideal "stacking" arrangement of particles is called "card stacking": which means particles are arranged tightly and uniformly. If the particle charge supplied by Darvan or by SS and soda ash is too low, or temperature is too low then they stack by particle size (A!B!C!) or "flat stacking" which results in warping. The ideal temperature is 90-100F, at which point temperature actually aids in suspension. The maximum temperature is 140F.

Applying this principle visually: maple syrup is firm in the freezer, thick in the refrigerator, heavy at room temperature: and thin when heated. The temperature directly impedes or accelerates particle suspension by allowing/hindering particle motion (collidial chemistry.)

Tom

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@glazenerd Wow 90-100F that is much higher than expected. Thank you so much for the explanation that really helps! 

Do you think the ambient temperature of the room that the object is drying in matters? I'm assuming that all the particles would be aligned relatively soon after the object is done casting so could I dry the wares in any temp room within reason?

Thanks again for the help,

Cole

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Cole:

Fred is correct: temperature of the slip effects ionic charge: which in turn effects particle stacking. F.H. Norton PhD @ MIT Wrote the original theorems on slip chemistry back in 1948. IF your slip is formulated correctly, deflocculated correctly, and the temperature is correct: then setting should occur within 15 minutes. Temperature of the mold could double that time. The other variable is soluble salts: which in modern times would be Nep SY used as the body flux.There were numerous studies done on the effects of soluble salts on casting rates, viscosity, particle suspension, and segregation. Those studies showed that soluble salts should be kept under 0.30%, which brings us back to Nep SY with up to 14% soluble salt content. 

If you can keep the temperature of the slip and molds at 75F, it would alleviate your warping issue. You would have to do absorption testing to verify the effects of soluble salts. EX: if your premix slip states 2% absorption at cone 6, and testing shows 3-4% at cone 6- then you are still dealing with particle segregation caused by either temperature, soluble salts: or both.

Tom

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