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Clay Ph


Min

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I use a slip that is mostly OM4 which I need to reduce the shrinkage of. Slip needs to be alkaline when applying to green ware, will calcining part of it alter the ph? My other thought was to add a tiny bit of soda ash, in place of part of the 3134, to increase alkalinity if necessary. (slip is for mocha diffusion and on my clay it either cracks or gets gritty from lifting slightly) Anybody done this or have any thoughts?

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Waiting also

Do clay mfgr's. Control ph of water to control ph of clay.

 

I'm also thinking does water Impurities affect clay body dramatically. Eg city water vs.. Well water vs collected rain water. Rain water tends to be sweeter, well water tends to have higher minerals especially sulfur, city water has chlorine....., How do these affect clay bodies?

 

Inquiring minds want to know?

 

Why does slip need to be alkaline?

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Big Lou, Min wrote that she was doing a mocha diffusion which I think is the effect of an acid on the slip causing an attractive patterning, if coloured slip is used on a white one.??, as the acidic slip diffuses into the alkaline one, I think.

Thought clay was naturally alkaline?? Silly statement???

lots not to know!!

Didn't link her need for alkalinity to the adherence to clay body......

Watch this post all will be revealed,

NOT in my posting!

I'm merely thinking around this before reading up on it if it stays in my brain.

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Is adjusting the ph with something that burns out (vinegar or a small amount of ammonia maybe?) helpful?

 

I had to look up mocha diffusion. That looks cool!

Thanks for the thought about adding ammonia to the slip. I calcined some OM4 last night and will start testing with that to see if is less alkaline than uncalcined OM4. The vinegar is in the "tea" that goes onto the wet alkaline slip causing the reaction which makes the dendritic patterns. I wonder if nasty gasses are released if I add ammonia to the slip then put the vinegar onto that? Maybe I should try that one outside  :wacko: 

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I wonder if this helps:

 

http://www.ias.ac.in/matersci/bmsfeb2001/57.pdf

 

First, it suggests that adding ammonia to your deflocullated slip is not just fine, but a good idea. I had no idea that driving the pH up to 9-11 gives the best viscosity--who knew it was that basic. I don't think there is a toxic potential for adding the ammonia, either, as long as you haven't previously added bleach for any antibacterial/antifungal reasons. (NH3 + Cl = killer) NH3 + CH3COOH (vinegar) is fine.

 

I also wonder about your idea of adding ash. It might help your slip adhesion too, along with altering the pH.

 

Do you use oxides as your stain, or are you using mason stains? Mr. Hopper states that oxides can't be carried in solution as well as carbonates. What works for you?

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drmyrtle, thanks for the link. I'm not sure if it pertains to ceramic clays? I haven't seen a clay that has silicon nitride in it, I wonder what it's used for? I'll pick up some ammonia tomorrow and give it a try in place of some of the water, I'm curious as to what it will do. I've used oxides, carbs and stains in the acidic tea over slips with RIO or stain. It's just my current clay that is being a bugger, I've not had problems with any of the previous clays I've used mocha on. 

 

BigLou, I couldn't find anything here either. I did come across a CAD article that has one line in it saying a ph of 6.5 is ideal for plasticity. The article is here: http://ceramicartsdaily.org/ceramic-supplies/ceramic-raw-materials/the-particulars-of-clay-body-plasticity/

 

Thanks for all your suggestions!  :)

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I find ammonia fumes pretty nasty.  Pretty caustic  thoug don't know quantities, just don't go sniffing the bottle to see what it is!!

Soda ash is a defloc right?

There's always that one turkey in the studio that wants to try peeing in the reclaim for the sake of "authenticity." (Ewwww!)

I had some classmates that did exactly that. Their clay wasn't any more pungent than anyone else's.

Granted, urine is different than straight ammonia, but maybe just a little dab will do? I remember my grandmother putting a few drops in her dish water, and she washed bare handed.

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Min, does your slip recipe contain any feldspar?  I think the alkalinity comes from that in the recipes I've seen.

 

It has 5% custer in it. I've made it with part ball and part kaolin with decreasing amounts of the former and increasing amounts of the latter. As the kaolin goes up the effect from the vinegar etching goes down. I've also tried slip made from the claybody, lousy results with that also, it's a porcelain with no ball clay in it. Between the two tests I came to the conclusion it is the ball clay that is causing the alkalinity. Hopper's recipe  (ball 75, spar 5, silica 10, epk 10) plus I add 5  3134 and 10 RIO  It's lots of fun when it works, I first saw it done at a presentation done by Hopper. Instant drama on the pot.

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Huh.  Weird.

 

What's the kaolin you were using?  The significant alkaline component in OM4 is K20, EPK has 0.77% K20 less than OM4.  Grolleg on the other hand has  0.80% greater K20 than OM4.  Tile #6 has very little alkali of any kind.

 

I wonder if there's some other mechanism at work. Particle size?

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Deisel clay Right, myth re aging clay for next generation, peeing increases plasticity. or lazy potter does not want to brave the cold, frenetic potter leaves no time to go to toilet......

yes, bottle of caustic soda or ammonia washer woman's friend in areas of hard water. Makes for suds and soft,( eaten away??) hands.

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Huh.  Weird.

 

What's the kaolin you were using?  The significant alkaline component in OM4 is K20, EPK has 0.77% K20 less than OM4.  Grolleg on the other hand has  0.80% greater K20 than OM4.  Tile #6 has very little alkali of any kind.

 

I wonder if there's some other mechanism at work. Particle size?

 

EPK for the kaolin, OM4 for the ball. 

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Min, I believe that the reference is related to porcelain slips used for dental applications. I thought it might be of help because they were looking specifically at the addition of nitrate/ammonium to porcelain slip.

 

Babs, if that article is relevant (?) then it would explain why soda ash would act as a deflocculant, since the viscosity of their medium decreased dramatically at higher pH's. I take this to mean that the particles move more freely around each other (not in bird flocks) when you make the solution more basic. Since lye (from ash) has a pH in the 9-11 range, I'm thinkin' that the addition would help deflocculate a slip/solution.

 

As always, I come at this without the advantage of specific ceramics material training, and I hope my obtuse references are relevant and/or useful.

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