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Help! Hand-Dug Clay Needs Additive For Strength

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My husband recently dug clay from a clay hole that his tribe has used for years, and the clay vein was so smooth that the clay peeled off the walls of the clay hole.  He and other tribal members thought they'd found the best clay yet from that spot.  It's now been dried, screened, soaked and dried to workable consistency. It wedged up beautifully but they find that the clay has no strength!  A coil-built pot sags under its own early weight.  

 

His thought is to return to the clay hole and dig what he would consider poor clay, process it, and add it in.  But I wonder if anyone has a suggestion about an additive that would add significant strength without drastically changing the color of the clay, which is a deep brownish- grey color, which fires to a tan or yellow-brown.  This clay is slightly darker and more grey than the clay that is usually acquired from the hole, making us wonder what is missing.  The pots will be burnished, preheated to 500 degrees and fired on the ground in the traditional way. Any help is greatly appreciated, since the clay hole is inaccessible during hunting season, which has begun.  I've attached an image of a fired pot.  

 

Thanks, Jayne 

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you might try bisking some of the clay, hammer it and sieve it to fine sand size or a bit coarser  and adding it back into the raw clay much like grog is added to other clay bodies.

It should give strength an the color would be the same

hope this helps

Wyndham

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I'm not sure what brands of clay you have available to you but you might be able to find a Raku clay in a dry form that fires to a similar color. Mixing it with the dug clay may give you the strength you need.    Denice

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Wyndham, thanks for the suggestion. As it happened, I was just starting a long preheat prior to bisquing my sculptures, so we rolled out super thin pieces of the hand dug clay and added them to the kiln. Being paper thin, the bisqued bits of clayshould be easily crushed. Do you have a suggestion regarding the minimum % of additive to clay? That is, an idea of a place to start wedging it in and testing it?

 

And Denise, that's a good idea for the long run. I'll look into just what my local clay retailer has. Highwater Clay's office is just a couple of hours away, so if it's not available locally, that's an option.

 

Colby, your suggestion is imminently practical, but there is evidence that my husband's tribe has been making pottery in this area for ~6000 years, and continuing to follow the traditions is their way of honoring their ancestors. It is impractical, given what is now known about clay and firing techniques, but to stray very far from tradition would be considered unethical in the making of Catawba pottery.

 

Thanks to all for offering help. My husband hasn't been able to reach the traditional clay hole for months due to rain, so finding that this beautiful, silky clay was unworkable was a real disappointment.

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Not sure on this but is the addition of paper appropriate ? Is the clay warping in the making process or in the firing process. I think there was dialogue here sometime ago to the effectthat grog actually weakens the clay body.. smallcracks forming around the grog pieces. Sculptors add paper for strength in the making process and lightness in the end result.

Hope someone else can comment on this.

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Jayne, I believe your husband might have struck upon a layer of especially silty clay. Silt, as it occurs in hand-dug clay, is a semi useless component that can make an otherwise wonderfully plastic clay body unworkable.  Silty clays will feel plastic and silky, but will also feel deceptively thin, with an awful tendency to slump and act strangely.  It should make a clay body stronger, in theory--it's veg. matter incorporated into the clay body, but it's such finely levigated muck that it does nothing but badly weaken your clay in really weird ways and contribute to LOI and drying issues.  

 

Edit:  Talking to a geology person today got me understanding this a lot better.  Silt isn't vegetative matter, it's rock dust, like clay, but it doesn't have clay's particle structure, and therefore doesn't have its charge or strength.  Silt is the cause of the feeling of silky smoothness, but it's not vegetative matter, just differently structured rock dust.

 

All hand dug secondary clays will be silty to some extent, and it varies almost by the seasons as you dig.  Commercial clays separate out the clay.  If you'd like a DIY approach to that process, check out Michael Cardew's Pioneer Pottery.  He outlines it in his appendix on brick making.  I believe it's also covered in "the Self-Reliant Potter" Series.

 

This may be unnecessary though, since by the sounds of things the water making the clay hole inaccessible might be the cause of the silt, and your husband simply needs to dig out the recent silty additions.  Digging out wider might make for a more consistent clay product.  I've noticed something about the way the old brick and tile yards worked around SW Ontario using local clays--They found a layer and stuck with that rather than digging up or down. pits 15 feet deep and an acre in size.  The terracotta just south of Woodstock, Ontario turns from a hard, salmon coloured cone 06, to a soft, chalky cream that crumbles in your hands at the same temp.  Obviously you've only got so far to go...

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Babs, I think this clay is well beyond saving with paper additions, even if it were an acceptable practice.  

 

Tyler, thank you for your insights into this. It all makes perfect sense, given the fact that the clay vein is located near the Catawba River in lowlands.  Regarding digging deeper vs wider:  this centuries old clay hole, long kept a secret from outsiders, was bulldozed over several years ago by the white owner of the land where the Catawbas have been digging clay for as far back as memories and stories recall.  It was done to make access to other areas more convenient for the farmer who rents the land from the landowner!  It was a blow, but the Catawbas persevered, as they always have, and resumed digging in the same area, although from atop the soil that had been pushed over the hole.  For a better understanding of the subject, we will check out your suggested sources.  Any other sources that you think might help would be welcome.    The potters have no understanding of or knowledge of clay's composition; they've simply always gone by "feel" and this clay was deceptive in its feel.  I've attached a photo, taken around 1985 of my husband standing in the former clay hole, handing up freshly dug clay to his 85-year old grandmother, who would tear away the undesirable bits and toss the rest into a bucket for her grandson to schlep out.  That trench no longer exists.

 

My husband dug 700 lbs of this clay that day, carrying it in buckets great distances to his truck.  Is it utterly worthless as clay or do you think it can it be saved with additions?

 

Grateful for the help, Jayne

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Neil, it looks like there's going to be a lot of experimenting with different solutions.  For your suggestion, what proportion would you suggest starting with?  Could it be wedged into the wet clay, or would the clay need to be turned back to slip before adding silica and ball clay/fireclay?

 

Thanks, Babs.  Yeah, I like that picture, too.  I remember that day as one of the best of my life. (probably because I wasn't standing in the ditch lifting out clay that ended up in reject piles around his grandmother's feet!)

 

Jayne

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Tell us the process of how the clay is made?

Has any QC been done ok pn kiln? Are you firing with witness cones?

I like goldart.... It tends to be great equalizer when making clay.

But I like what Neil said, mixing up particle sizes

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Lou, the clay is dug from what I suppose you would call river bottoms.  Before there were vehicles, the Indians paddled canoes across the river to this patch of land to collect clay.  (The clay was so desirable that the North Carolina Cherokee would travel - sometimes on foot - to South Carolina to acquire this clay from the Catawbas.) This clay is used to make small bowls, peace pipes, etc. But to make larger bowls, clay from a different area had to be added in at the proportion of 1 part strengthening clay ("pan clay") to 4 parts river bottom clay ("blue clay").  That clay could be found in many places.  The clays, full of debris and rocks, are spread to dry in the sun, after which the debris and rocks are removed by filtering through a window screen. (Before there were screens, it was simply picked out by hand.)  Then the clay is covered with water until it has become a smooth slip.  That slip is poured into a pillow case or onto a cloth covered surface and allowed to dry to workable consistency.  It is wedged and formed into coils.  The process is unscientific, with the quality of the clay judged by feel, with one generation teaching the next generation.  If you look at the earlier posted photo of Bill handing clay up to his grandmother, clumps of rejected clay are scattered around her feet.

 

Traditionally, the clay has been strong enough to withstand a punishing firing system. After preheating pots next to a fire or in a fireplace (or for the last half century, in an oven), the pots are placed in the hot coals of a fire that has burned down.  Then another fire is built over the pots with small pieces of wood.  As that fire burns down, layers of pine bark strips are laid over the pots to smother the fire and create the characteristic shiny black and grey areas.  This firing takes place on the ground or in a very shallow concavity, a method that is risky to the pot and to the potter.  In fact, a tribal elder recently lost her home to a fire that spread when she was burning pots.  

 

Catawba pottery is not as widely known as many western tribes' pottery, but Bill's grandmother Georgia Harris had a one-woman show at the Renwick and is the only person to have been posthumously awarded the Folk Heritage Award by the NEA.  In their press release in 1997, they wrote about Catawba pottery:

      In the western United States, many Indian pottery traditions thrive and enjoy wide recognition.  In the east, however, few Indian pottery traditions survive, and only one - that of the Catawba of South Carolina - maintain a direct connection to the pre-conquest past. "The Catawba potters constitute the only group of potters east of the Mississippi River which has maintained this aboriginal art form in a nearly pure state from pre-Columbian times to the present" according to Catawba historian and culture scholar Dr. Thomas J.Blumer. 

 

So, no, there is no QC or use of witness cones or anything more nontraditional than using an oven to preheat the pots.   I hope this answered your questions?

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You might get in touch with the SC state geologist office. they may have mapped that area and help find a new deposit near by and accessible .By describing the color to a geologist may help him pinpoint other deposits for you.

What part on SC are you referencing, just wondering.

We have a local clay called Buck Tallow that is silty muck but other clay that works well is under this seam.

 

As to the bisk, trial & error

Wyndham

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Amazing story, history........i want to visit now..... I was thinking of Catawba valley pottry ...groundhog like kilns. Didn't think to trace back to Catawba tribe!! This takes it to a whole different perspective, pottery wise and historically.!!!! Pottery at its purist!!

 

Part of me wants to tell you don't mess with tradition. As in fixing the clay with modern / foreign ingredients., What would grandma or others elders say...regarding clay?

 

Another part of me wants to fix clay in least invasive method. And from the scientific side find out why this last batch is not working.

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My husband, who works 60-70 hours a week as Chief of the Catawba Nation and soooo looks forward to weekends when he can put his hands in clay, asked me to express his appreciation for all of your help. You have offered a lot of potential solutions and he will be pursuing them all in an effort to salvage this clay for himself and other tribal potters who were initially thrilled with what looked to be a fine clay vein. 

 

Wyndham, the Catawba reservation is an area of under a thousand acres about 30 miles southeast of Charlotte NC, and about 10 miles east of Rock Hill, SC.  In 1760 the King of England granted the Catawba Nation 144,000 acres straddling the NC and SC border.  In an illegal treaty, the state of South Carolina "purchased" that parcel in 1840, leaving the Catawba homeless until a white settler gave a 630 acre parcel to the state to be held in trust for the Catawba. The Catawba sued over that illegal treaty and settled for $50,000,000 and federal recognition in 1993.  That parcel is the core of the present Catawba Nation. 

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Amazing story, history........i want to visit now..... I was thinking of Catawba valley pottry ...groundhog like kilns. Didn't think to trace back to Catawba tribe!! This takes it to a whole different perspective, pottery wise and historically.!!!! Pottery at its purist!!

 

Part of me wants to tell you don't mess with tradition. As in fixing the clay with modern / foreign ingredients., What would grandma or others elders say...regarding clay?

 

Another part of me wants to fix clay in least invasive method. And from the scientific side find out why this last batch is not working.

Lou, you made me smile with your reference to Grandma, which is indeed what even I called Georgia Harris.  She would have been dubious about anything a "modern" potter could offer, but she would have been practical enough to consider it!  On the other hand, with 75 years of experience as a potter, she wouldn't have been fooled by this clay vein!  

 

Since you like history, I thought I'd share this image of a turn-of-the-century Catawba potter named Sarah Harris.  I can't imagine sitting as she is and working on hand-built pots!  It makes my back hurt just thinking about it! 

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Dandasana! a powerful  pose. Try it Jane sitting on a firm cushion, stting bones right on the front edge of the cushion, you'lll be there in no time. Right in the moment. I can see you making those beautiful canoes for Bear! :)

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There are lessons on particle size theory avaialble from Alfred U. I'm thinking the part of vein/veins harvested have too fine a particle size. One part basically states for stronger body with grog additions use 50%coarse 40%fine 10% medium . The same theory applies to clay bodies too much of one particle size make for weaker body. For your body, get those castaway stones and "mill" them down and re introduce to clay body. My mill consits of 5 gal plastic pickle bucket and 8# sledge hammer. Think butter mill action. Then screen results in coarse med and fines. Or just screen out extra coarse and use the rest. This way you still have a "true" clay and natural solution. I have more ideas but they all move away from indigenous sources.

 

Other than pots slumping does it retain all other traditional qualities?

 

( I really pulling for a indigenous solution)

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What color does the "Blue river clay" fire to?  I have some, that a Science teacher brought in for me.  They found it on their property, near a stream.  It looks blue green, but turn golden yellow, when fired.  It's fairly weak, even when fired.  I made a test tile, and was able to snap it by hand, once it was bisqued.  

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Dandasana! a powerful  pose. Try it Jane sitting on a firm cushion, stting bones right on the front edge of the cushion, you'lll be there in no time. Right in the moment. I can see you making those beautiful canoes for Bear! :)

Babs, Given that I have two very curious and large dogs who share my studio, I suspect that the Dandasana pose may do wonders for me but not for my production schedule!  I can just imagine the broken sculptures that would result from working at dog-level! 

Jayne

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O.K., Lou.  You're right.  Grandma would prefer that Bill and the other potters find an indigenous solution!  So he will try crushing the rocks that were removed and adding them back in.  We read that grog can be added in at 10% for throwing and up to 80% for building.  What would you suggest as a starting place for additions?  And would you suggest adding only the crushed rock or combining it with sand and fired/crushed clay and adding that mixture to the too-fine clay?  Or perhaps we should limit the variables and add only the crushed stone to one batch of clay, sand to another batch, and fired and crushed clay to another?

 

It's hard to say if it retains the other traditional properties, since no one has gotten any further than half-built bowls with this clay.  

 

Bill came home from the tribe's Longhouse today chuckling about the fact that the other potters are blaming him for the bad clay, forgetting that when they saw what he had dug they immediately began digging in the same place.  It fooled them all.  But I think you've all figured out the problem, and just understanding what makes this clay "work" (or fail to) is a huge relief in itself.  Now we just have to figure out the proper additions and proportions....

 

By the way, for the sake of simplicity, the tribe's employees are given the usual federal holidays, which includes - and yes, it is beyond ironic - Columbus Day, the day that Columbus "Discovered" the Americas!  So Bill has a long weekend to play around with all these suggestions!    

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Benzine, disregarding the smoke effects of the pine bark, the clay fires to a range of colors from tan to yellow to amber. Interestingly, I've noticed that the older pots tend to be lighter in color.  About 20 years ago, we came upon an unsigned pot at a flea market that Bill instinctively believed to be the work of his grandmother's grandmother, although he'd only seen one of her pots in an old photograph.  He told the seller what he believed it to be and happily paid the $18 price.  When we showed it to the acknowledged authority on Catawba pottery, Dr. Thomas Blumer, he immediately and excitedly confirmed that it was a rare example of the work of Martha Jane Harris, Bill's great, great grandmother. A beautiful cork color, it is on the left in the photo attached. For the last five generations, pottery-making seemed to skip a generation in his family, so that the pot on the right is Bill's, in the middle is his grandmother's, and on the left is the pot we found at the flea market, almost certainly the work of his great, great grandmother.

 

Jayne  

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I'll put my two cents in..Fill half of a glass quart jar with your clay. Fill the rest of the jar with water. Let it slake and settle for 2-3 days. If it layers out, the lowest layer will probably be silt. Scoop off and save the top 2/3 to 3/4 and let this dry to a workable consistancy. Try Throwing or building with the newly dried clay. Discard the lower level.

 

If this improves the clays workability, then repeat the process using 5 gallon buckets.

 

Jed

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