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Natural Dug Clay, Need Help


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I’ve been digging red clay dirt in my back yard and wet processing it.  I cannot get it into a plastic state.  It’s really short.   I’ve tried everything that was previously suggested and then some.  I’ve added Bentonite.  I’ve added epsom salt (which almost seemed to make it worse).  I’ve tried redrying, pulverizing, and rehydrating.   I even bought a 200 mesh sieve to get only the really fine particles.  What is the problem, and is there any hope?  Thank you!

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Hi DJJ!

Whilst waiting on response (from clay experts), could you post some pics of your clay (wet, formed, dry, fired...) and identify the location?

Folk have been digging, analyzing, classifying, documenting, etc. clay deposits for quite some time; the location might help generate a helpful response - county (in North Carolina?) might be close enough.

fwiw, I'm adding a small amount of 80% OM4 ball clay, 10%feldspar, 10% silica to my reclaim (commercial wet pugged); doesn't take much to change the working properties!

Hopefully, experienced natural clay harvesters will chime in here...

Edited by Hulk
approximate location
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2 hours ago, Hulk said:

Hi DJJ!

Whilst waiting on response (from clay experts), could you post some pics of your clay (wet, formed, dry, fired...) and identify the location?

Folk have been digging, analyzing, classifying, documenting, etc. clay deposits for quite some time; the location might help generate a helpful response - county (in North Carolina?) might be close enough.

fwiw, I'm adding a small amount of 80% OM4 ball clay, 10%feldspar, 10% silica to my reclaim (commercial wet pugged); doesn't take much to change the working properties!

Hopefully, experienced natural clay harvesters will chime in here...

We are in Kings Mountain NC, about 30 miles west of Charlotte.

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10 hours ago, DJJ said:

I’ve been digging red clay dirt in my back yard and wet processing it.  I cannot get it into a plastic state.  It’s really short.   I’ve tried everything that was previously suggested and then some.  I’ve added Bentonite.  I’ve added epsom salt (which almost seemed to make it worse).  I’ve tried redrying, pulverizing, and rehydrating.   I even bought a 200 mesh sieve to get only the really fine particles.  What is the problem, and is there any hope?  Thank you!

You are dealing with a property called "cementing."  This property is created by higher iron and alumina content which creates strong positive charges that "cement" particles together. It can be further compounded by the acidity of the clay. Without going down the clay chemistry rabbit hole: perhaps simple math. Negative charge = plasticity. Positive charge = cementing. In addition: alkalinity = deflocculation= plasticity. Acidity = flocculation= cementing. Cementing can be better understood as tight compaction/adhesion of adjoining clay particles. The solution requires more than just adding plasticizers; requires more chemistry than that. Start with a minimum addition of 10% Nep Sy or Mahavir potash (or whatever KnaO flux you have available to spike the alkalinity. You also need a broader dispersion of fine particle ball clay such as OM4, FHC, C&C, or other commercial ball clays. The starting point would be 65% wild clay, 10% Nep Sy (body flux, 15% OM4, and 10% silica. Start with a 1000 gram sample and test. Remember, plasticity can take 5-7 days to develop- it is not an instant reaction.

Tom

 

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19 minutes ago, glazenerd said:

You are dealing with a property called "cementing."  This property is created by higher iron and alumina content which creates strong positive charges that "cement" particles together. It can be further compounded by the acidity of the clay. Without going down the clay chemistry rabbit hole: perhaps simple math. Negative charge = plasticity. Positive charge = cementing. In addition: alkalinity = deflocculation= plasticity. Acidity = flocculation= cementing. Cementing can be better understood as tight compaction/adhesion of adjoining clay particles. The solution requires more than just adding plasticizers; requires more chemistry than that. Start with a minimum addition of 10% Nep Sy or Mahavir potash (or whatever KnaO flux you have available to spike the alkalinity. You also need a broader dispersion of fine particle ball clay such as OM4, FHC, C&C, or other commercial ball clays. The starting point would be 65% wild clay, 10% Nep Sy (body flux, 15% OM4, and 10% silica. Start with a 1000 gram sample and test. Remember, plasticity can take 5-7 days to develop- it is not an instant reaction.

Tom

 

Thank you Tom.  Excuse my ignorance, as I’m new to this, but what is Nep Sy?

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3 minutes ago, DJJ said:

Thanks.  Could wood ash be used to make the clay more alkaline?

Yes, wood ash could be used. Trees pull calcium and potassium from the soil, and often other alkaline. Cannot advise you on how much to use because the amount of alkaline is directly related to the soil it grows in. Good place to start would be 2-3% because of the weight differential between ash and minerals (Nep Sy) 

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My experience is by the time you add all the additives to make natural dug clay work in a mondern way (wheel throwing etc)its much easier and chaeper expecially labor wise just to buy clay.

Sure backyard clay is fun and it not always about money but to make this clay work its really not much different than commercial clay in the long run.It needs lots of additive and will always have some drawbacks.

 

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I would like to know where you are gathering it from and how, also your entire processing process.

There is a lime test you're supposed to administer using hydrochloric acid. Too much lime and you're fighting an uphill battle that may be unwinnable.

Further, I recently brought a seive out to collect with and ended up with more sand than before. Backwards of what I imagined, so be careful of what else you may be collecting.

I think aging is also important.  Nothing you can add will replace time.

If you use wood ash, make sure it is clean and white, otherwise you'll be introducing morganics, which will make it harder to refine.

I agree with Mark, but if you can make a product, any product, with your clay, and either enjoy making them, or can sell them, it could be worth the initial investigation.

Sorce

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There may be lime.  It might be worth a test.  
My process is pretty simple, just dig from about 3-5 feet with a post hole digger, dry the dirt, dump it into a water filled bucket, mix it, sieve it first using a regular kitchen sieve, then fine sieve using a 200 mesh sieve, mix it with a drill mixer, drain water after it settles, pour slurry into a pillow case, and dry it out to workable consistency.  I usually let it sit for a few days in a plastic bag before wedging it.  
Funny thing is, I actually got more plastic clay before I started using the 200 mesh sieve.  Maybe someone can explain that one.  Perhaps the finer clay is more susceptible to cementing as glazenerd pointed out.  

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8 hours ago, Callie Beller Diesel said:

I’d be concerned about using wood ash. It can be quite caustic in glazes, especially unwashed. 

I already tried adding ash to a few of my clay chunks.  I wedged it in with rubber gloves.  How long would it remain caustic before I risk touching it do you think?

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1 hour ago, DJJ said:

I already tried adding ash to a few of my clay chunks.  I wedged it in with rubber gloves.  How long would it remain caustic before I risk touching it do you think?

Depends on how much acid there is to react with it.  If there's a lot of acid you can touch it right away, if there's very little to no acid it'll likely always burn you 

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What Liam said. Another problem with wood ash is that it’s so variable in composition from batch to batch. Typically anyone using ash in a glaze will create a large batch, or homogenize several smaller ones so that results will be consistent over time. 

You're already dealing with one variable material in the form of a “wild” clay.  I would think it’d be a lot easier to amend with ball clay and neph sye as recommended, at least until you’ve worked with the clay enough to establish what it’s working properties are. 

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Yep! Definitely you can test the pH of it. Make a slurry with distilled water and a dry piece of the mixed clay and test the water.

But as glazenerd said, it takes a week or two to develop plasticity so it may continue to react for that period.  Perhaps test it a few times over that week.

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2 hours ago, DJJ said:

There may be lime.  It might be worth a test.  
My process is pretty simple, just dig from about 3-5 feet with a post hole digger, dry the dirt, dump it into a water filled bucket, mix it, sieve it first using a regular kitchen sieve, then fine sieve using a 200 mesh sieve, mix it with a drill mixer, drain water after it settles, pour slurry into a pillow case, and dry it out to workable consistency.  I usually let it sit for a few days in a plastic bag before wedging it.  
Funny thing is, I actually got more plastic clay before I started using the 200 mesh sieve.  Maybe someone can explain that one.  Perhaps the finer clay is more susceptible to cementing as glazenerd pointed out.  

Your processing methods are fine: need to move on from that. Wild clay often have Organics which can add some/or much plasticity. Some are removed during wet processing- normal/desired: the 200 mesh sieve removed the rest. 200 mesh sieve is really not necessary, although I understand the why. Typically 60 or 80 mesh screens are the norm. Remember, the fly ash is only being used to spike alkalinity; not as a body flux. Harvesting wild clay is the roots of modern pottery; much more popular than most realize. There are deposits that can be used straight from the ground and onto the wheel, but uncommon. The limitations being accepted as non-functional use unless formulated and tested. I have the good fortune of having recieved clay from across the USA. My favorites so far have been magnetite (iron) from New York and hematite from Oklahoma. Speaking of cementing: sub-tropical laterite from India tested at 43% alumina &13% iron (4.65PH)required nearly 20% Nep Sy just to neutralize the strong positive charge. 

Tom

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