Sheer Thinning

[glazenerd]

Stumped...well sorta of stumped.

 

Cone 04 porcelain frit-ware has some chemistry, that I find challenging. I recall Min talking about having to heavily wedge a Plainsman body that had V-gum T plasticizer. The most colloidal plasticizer used in the pottery biz, to impart plasticity into an otherwise non-plastic formula. Works well for plasticity, but it holds water much differently than more common materials like bentonites or ball clays. The exterior of the ball may be correct, but as you wedge more moisture is pushed to the surface. After wedging numerous times: the problem persisted.

 

 Checking the chemistry of 3110, there is little boron sourced. I can only assume this is sheer thinning going on. If it is sheer thinning, how to overcome it?  hmmm.

 

Nerd

[tinbucket]

I would contact the materials guru Tony Hansen of Plainsman Clays and Digitalfire

[glazenerd]

Triolaz:

I did a search on his site: nothing came up. Doubt seriously this is an issue Tony has addressed. Suspect a wetting agent, or other regent will be needed to deal with this chemistry issue. Find it rather odd that frit would be interfering with colloidal materials. Definitely a chemical reaction: just have to figure out exactly what it is.

Nerd

[curt]

Pretty sure Veegum T is just a smectite, so not sure why it would act differently in relation to water than other smectites?

 

Shear thinning is a liquid thing. I don't think it applies to clay bodies which are much too stiff. Slip, maybe, but not clay bodies.

 

Perhaps the Frit, as a completely non-plastic material, is forming little micro-channels which are wicking interior moisture to the surface. Any evaporation taking place would speed this process along.

 

Is the clay sweating?

[glazenerd]

Initially, then it stops after a day of being left open. I slab rolled out the entire test batch several times on Bralizian luan: which wicks a lot of water. Wedged it back into a ball; left it over night: still thinning the next day. A real oddity. It has to be some reaction of the frit: have used V-gum in pure porcelain with no problems. Used it in other bodies, no problems. When frit is added.. problems.

 

Shear thinning just means liquid moves/displaced when mechanical pressure is applied: wedging in our case.

 

Nerd

[Min]

If it helps the porcelain I was referring to is this one. $70 for a 44 lb box and you can't use it right out of the box. Would swear it's way to hard and dried out when you open a bag, wedge it up and it's too sticky wet. Dry it out a bit then wedge and it's fine. Let the balls of wedged clay sit for a bit and they need to be re-wedged. It does throw nice once you get it sorted out but the cost is too much for my everyday pots plus the time it takes to get it workable. (I'm just using it for small stuff like wedding favours now) Tom, you've seen Tony's 03 fritted porcelain right?

[curt]

Not sure what Bralizian Luan is, but it sounds like serious stuff!

 

Shear thinning is a much more specific phenomenon than just pushing water around by force. It describes temporary changes to the microstructure of the whole material, not just the water in it. Think house paint and ketchup (hat tip Wikipedia) and how they work when you touch them. Thick, then suddenly much thinner when you move it, then a second later thick again. Clay bodies don't work this way (at least mine don't).

 

Point is, I don't think seeing this as shear thinning will move you in the right direction to understanding what is going on. Just my two cents.

[glazenerd]

 

Min said Would swear it's way to hard and dried out when you open a bag, wedge it up and it's too sticky wet.

 

Curt said: Thick, then suddenly much thinner when you move it

That is sheer thinning. It describes the mechanical issue; but the source of it is chemical. Have to figure out how to resolve it. Only the 04 fritware displays this issue.

 

Brazilian luan works much better than gypsum board for tile. It is pricey: $40 a sheet. But I have been using the same sheets for over 6 years. Cut in 2 x 4 sections, send it through the slab roller with clay on it: cut the tile, and leave it.

 

Yes Min, I have seen Tony's 04 fritware recipe. He uses 3% V-gum, little heavy for my tastes.

[glazenerd]

HYDROLYSIS reactions.

 

donnan hydrolysis, to be more specific. Frit has been thermally disassociated by the first smelting: so the resulting frit would only have sodium cations available: making it hydrophilic instead of hydrophobic.

 

Plain clay English: sodium in a clay body would normally accelerate drying ( hydrophobic), the sodium in frit has been physically altered from heat: causing it to be hydrophilic ( wants to store water.) which explains why the face of the clay has normal consistency, and the interior is mushy because the frit is holding water.

 

That is my best guess.

[Min]

HYDROLYSIS reactions.

 

donnan hydrolysis, to be more specific. Frit has been thermally disassociated by the first smelting: so the resulting frit would only have sodium cations available: making it hydrophilic instead of hydrophobic.

 

Plain clay English: sodium in a clay body would normally accelerate drying ( hydrophobic), the sodium in frit has been physically altered from heat: causing it to be hydrophilic ( wants to store water.) which explains why the face of the clay has normal consistency, and the interior is mushy because the frit is holding water.

 

That is my best guess.

 

except I highly doubt there is frit in the Polar Ice ^6 porcelain. 

[Mark C.]

( $70 for a 44# box)

I'm out of business at that price-just on the clay forget the glaze and firing cost-this is strictly a hobbist body or a sculpture body.

[Min]

( $70 for a 44# box)

I'm out of business at that price-just on the clay forget the glaze and firing cost-this is strictly a hobbist body or a sculpture body.

 

Yup! My wedding favours / ring dishes little things use 4 oz of clay, I can get around 175 of them out of a box and sell them for $5- each, so that's $880  I do use it for small sculptural pieces too, but for everyday pots, nope. Brings up the question of how much would you pay for a claybody. 

[Mark C.]

Clay is the cheapest part of this business.

I to use a few high end porcelains for small work that makes the glaze colors pop.Like spoon rests and sponge holder-those clay bodies cost twice as much and my usual Daves porcelain .There is a need for specialized  bodies that cost more but that need is small.

One only needs a body that works well with your glazes throws well and works (no cracking or falling apart and vitrifies)-other than that 

(unless you need translucent) what else is there.

Myself I need a white strong porcelain that fires hard and is durable.My use is 10 tons a year and is going down. I'm willing to pay whatever that body costs. I do not need materials in this body from all over the globe that add costs-I do not need translucent clay.I also do not want glassified clay like frost. 

My clay is really cheap as I buy so much and have the 12 ton discount going (with an whole truck load) so I'm willing to pay more .

What I have found is when I was starting out I used about 10 clay bodies and over time it got down to just a few . I think this rings true to many starting out . The endless  search for the perfect body which for me is never going to happen. I think finding a body that works is really all one needs.Working though all the glaze choices along with all the clay choices is so much work-it really just adds to the confusion of a beginner .

Learning to build kilns and fire them also fits in this as well as different clays work better in different atmospheres and temps.Its all in the learning curve.

These days it seems that the mainstream is use an electric kiln and fire to cone 6.Cone 6 bodies seem to be particularly troublesome or at least that what this forum seems to point out? The funny part is I know of only one full time potter in my circle that does this in cone 6.