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How To Handle Unidentified Old Clay


susieblue

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So I just made a HUGE Craig's List score: a barely used, well-cared-for, mid size Duncan kiln (with pristine shelves), a phenomenal wheel made by a former potter (who is an engineer/industrial designer/machinist) and a ton of old supplies, including glazes, raw materials, chemicals and several buckets and boxes of dried clay. All for only $350!

 

Although I have had an off and on relationship with clay over 40 years I have never had the opportunity to really delve deeply into it until now so in some ways I really am a newbie.

 

My question: How do i know what kind of clay i have? It appears to be a mix of earthenware and stoneware. The potter who sold it to me said he fired mostly low to mid range. The kiln he sold me goes to cone 8 but he said never fired that high. The red clays i assume are probably low fire and the white he told me was very elastic so I am assuming it is a white earthenware...maybe?  I don't know about the brown and gray clay. If I treat everything like a low fire clay and use low fire glazes will I encounter problems?

 

I plan to take small quantities of each, slake and screen it so i can try it out when I am ready to fire.  Any advice? 

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You cannot assume the temperature of the clay by the colour. You have to test it all unfortunately. You really got the deal on the wheel and the kiln. If the testing of the clays is too onerous, just dump them. But not in your yard.

TJR.

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Will you have problems treating it all as low fire? If it's mid-fire clay, you might have issues with glaze fit and porosity, which will affect you if you're making functional pots, but not so much if you're sculpting.

 

4 different kinds of unknown clay? I'd be inclined to mix it with some perlite, peat moss and Portland cement and make an outdoor sculpture or a birdbath or something else decorative and unfired. Bigger headache to try and reclaim and then test all of it and figure out what it is.

But that's just my level of (no) patience and my need for some garden art speaking.

 

ps. I agree with Tom. For the price you paid, if you have to dump the clay, you still got a steal.

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No need to slake the clay to rehydrate it; just open the plastic bags, add a cup or two of water (depending on how dried out the clay is), close up the bag and then sit it in an empty 5 gallon bucket. Fill the bucket with water until the water level is just below the top of the clay. Let it sit for a couple of days. The water pressure from the bucket water will force the water inside the bag into the clay. Check after a day or two, add more water if needed and repeat, until you get a nice consistency.

 

At what temperature do you want to work? Cone 04/05 low temp or cone 6 mid-temp? If you want to fire to cone 6, then make some small test pinch pots of each of the clay bodies. Place them on a small bowl/dish made from known cone 6 clay. Fire -- if they are low-fire, the bowl will catch the melt; if they are mid-range, they'll be okay.

 

Same for testing glaze fit at low fire temps. Make up a couple of test tiles/pinch pots, glaze them with low fire glazes, and check the results. You have a couple of test firings to work out the question of what is what, but you can mix those test items with work made from known clay.

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I reread this post. I have to tell you that I love free clay and would do the testing. If the clay is leather hard, you can slice it up like bread-dip each piece in water and place in a bucket of water. Make sure the bucket water does not get inside the bag, or you get slurry.

Other options-

1.Use the clay as waster clay to make hump molds.

2.Make a plaster bat and use the clay to seal the edges.

3.Last option. Mix with saw dust and cement and coat your outdoor kiln.

Tom.

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LOL another Craigslist score, I love it.Congrats..  we got a deal not long ago as well.. we got about 100 lbs of clay and kept 25 lbs of ^6 white stoneware, had to hydrate it as it was bone dry .. it threw ok  i guess but it was some of the first clay we ever used.... 

 

we have 2 red clays here ,  one is a cone 6 and other a cone 5 ... 

we are cone 6 junkies for now so if you are looking for a good clay for ^6 i would suggest Little Loafers if you can get it in your area, its a very popular clay body.. 

 

Clay is cheap if it were me and i didnt know and i havent fired the kiln i just got, i would practice throwing with it and wait until i figured out what cone i wanted to fire.. if your like we were when we first started your going to make a few small pots here and there but your quality will improve 10 X of those  first pots you made.. give your self some time to learn  and ask questions when you hit a bump in the road, the folks here have helped us so much in a fairly short amount of time "sept. 2014" they still help lol ... we got pretty good at centering and opening up but pulling walls gave us fits .. It may take a little time and alot of clay to learn to pull.. it took us 175 lbs of clay and throwing every day we could then re wedging the older clay to keep both of us going... 

 

good luck to ya.

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congrats, craigslist is great.  and so is ebay except that anything with the word kiln in it will show up. there were a number of kilns under Kilns, used  the other day nothing near me but someone in illinois is going to get a real bargain!

 

if you can reclaim the clay, practice working with it and never fire the finished pieces.  spend some of the money you saved buying good clay once your skill level warrants firing something you have made really well.

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Thanks for all the advice. I will definitely save the stuff that was labeled (low-fire terra cotta still in the box). All the raw materials are labeled so I could just mix my own. He had the Newton Potters Supply Catalog (1973) so I know what all the model numbers/abbreviations mean.

 

I will probably try to reconstitute the the pure white to practice. I have taken several classes in throwing over the years and it does seem to be coming back to me. Youtube also helps.

 

I have to wear a mask to get this stuff all cleaned and organized since most of the plastic bags have disintegrated and there is loose white powder (whiting, zinc oxide, flint, and nephaline syenite) in large quantities in the original (opened) boxes. Not sure how to best store this since transferring it all to new bags or containers could raise a lot of airborne powder. Is that bad?.I know a lot of  materials are toxic and there are some glaze chemicals in this batch that can't even be purchased anymore. Will check out the sticky thread links to find out how to dispose of them. I don't plan to use any of the old glazes on food vessels since I know they are harmful. 

 

BTW: The guy I bought these from told me that he used to throw upside-down. I can't even fathom how he could do that.

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I'm a big fan of studio recovery clay. At one studio the recovery is all clays.... High low, red white ..... It comes out amazing and usually well behaved clay.

 

I tend to make most of my own clays, (glutton for punishment), I'd slop them all together, Pug and test.

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