Problems With Plasticity

[PuckGoodfellow]

First off, i would like to say hello to everybody. i'm new to the forum and haven't had the chance to fully explore the site. so consider this my formal greeting (with a dire plea for help). i'm a beginner when it comes to dealing with any kind of clay but i read a lot. i am currently trying to work with natural mined clay (dug out of the ground with my own hands). it's smelly but i can see it's potential. i have been able to refine the clay and remove all the things i don't want in there. my only real problem i'm having now is my level of plasticity. my clay won't pass the finger test (it cracks every time you bend it. unless you add way to much water). i'm hoping ya'll can help me. is there anything i can add to the clay to fix this. i know that i could age the clay but sadly i don't have 6 months+ to allow it to ferment and mature. i've read that i can add calcium lignosulphonate (apparently its a concrete additive that allows for less water and greater absorption. please correct me if i'm wrong) and it will greatly improve the plasticity, but i can't find it in quantities smaller than 1 metric ton. can i use ashes (i think i remember a teacher in school saying you could add willow or cat-o-nine tail fluff but once again i'm unsure and not willing to ruin my clay.)? somebody told me i could add sand but it seems to me that adding that would have the opposite effect. i feel as though i have exhausted google and youtube and i still don't have a solution to my problem and i don't know anybody with the experience to help me. i have 80+lbs of clay just waiting for the right answer so i can finally start creating things (and not having them want to crack apart while molding let alone when drying and firing). i want to make clay pipes and mug/cups (i'm saying this just in case it effects what i should add to the clay. i have no desire to make anybody sick or hurt them because i used the wrong additive). I have been bitten by the clay bug (HARD) but i've reached an impass. Please help me. Any and all information will be greatly appreciated.

 

i eagerly await your responses. 

i'm ready and waiting to satisfy this pottery itch.

I can't seem to think about anything other than clay now-a-days.

 

 

[Chris Campbell]

Hi and welcome.

You might want to copy and post this in the "clay and glaze" area where more people will see it.

There are many people on the forum who have used local clays and can help. You could even use 'local clay' and 'plasticity' as words to search this site for old discussions about it.

Good luck!

[Pres]

So I moved the strand to Clay and Glaze Technical

[Bob Coyle]

Sounds like you have a who;e lot of sand in this clay. Have you tried just rolling it out, letting it dry, and firing it to see if it will even hold together? Lignin will make a stick mess and probably not solve your problem. Unless this stuff will fire hard on it's own, I'm not sure it is worth the trouble. You may end up adding so much ball clay and other stuff to it that IT becomes the additive.

[Tyler Miller]

I've had a bit of experience working with hand dug clay.  I'll say from the outset that if it's not plastic directly from the ground, it's probably not worth your time.  If it's too plastic/shrinky, that's one thing, many solutions to that, but a lack of plasticity is tough to overcome without additives.  There's a lot of good news along with this though.

 

You can dig around in the vein you found the clay in and sometimes find a more plastic area.  If you're getting it from a bare field (like a farm), look for low spots where the clay cracks with its edges curled.  This is clay of a finer texture and will end up with a more plastic body.  It's a little more labour intensive to collect, but if you're insistent on hand dug clay, it's a possibility to use what you've got available.  Otherwise, contact a state/province/county geological survey and see if you can't find publications on the kinds of clay in their area and their firing characteristics.  Ontario, my home province, has excellent resources in this regard and I was able to pinpoint a clay seam (several, actually) to use with little trouble.  Well, it's been a long project to get it to work and figure out how to make it work, but much easier than if I were to go it alone.

 

Bob's got an excellent point about simply firing it and seeing what happens before anything else.  Sometimes you won't get what you want.  Lime pops, too much organic material, too much shrink, dunting, or a number of other issues could arise.  If it fires okay, and you don't have access to other clay, mixing in ball clay isn't the worst thing in the world.

 

You could also use it as a base for a glaze.  Developing glazes from local clay is much easier and more common than clay bodies.  Less work, sometimes wonderful colours.

 

I hope this helps you in your project.

[Bob Coyle]

 

 If it fires okay, and you don't have access to other clay, mixing in ball clay isn't the worst thing in the world.

I have used inexpensive bagged fire clay as an additive instead of ball clay. The stuff I got was pretty full of crap so you might have to screen it to make sure you get out big chunks. The river bank clay I found required almost 50% addition to get a throwing body. If I coil built, I could have used much less. fired well at cone 5.

[PuckGoodfellow]

Thank you for all the feedback (and relocating my thread).

 

It feels good knowing i finally found the right place to learn the things i need to know. i told you very little about the clay itself and yet you were able to nail one of the problems i was having and raise a concern (about my clay) for me. the "lime pops" comment worried me the most. my clay isn't found in any vain per-say. i located (i guessing) around 500+lbs of clay at the base of an old washing plant in a limestone quarry (hence my concern about lime poppage). the day i found it, the ground was damp but drying. The clay looked GREAT! the layer that had build up over the years was about 4 inches thick and had eventually formed the mortar holding the rocks on the abandoned road in place. Right out of the ground it was like store bought clay. But when i washed it down to remove the aggregate i found that my screen wasn't fine enough and felt to sandy. i was left with clay that felt like sandpaper when it was rolled into a worm and dried. I WAS able to form two medium sized pipes. one broke but the other one made it to the fire (it cracked in half as i was heating it up but other than that it did ok).  i broke it back down, got a finer screen (i'm stuck with lowes for my supplies due to a lack of a ceramics supply shop. the employees all look at me with confusion when i tell them what i'm looking for) and removed about 3-4 cups of sand from my clay. My screen still isn't where i want it to be (i've even doubled it up) but i would say that my clay is about 95% smooth. every morning when i dump the water that has built up on the top of my clay, i get enough clay on the side of the bucket to form a ball a little smaller than a smasher marble. i like where it's going but it still cracks a bit when i bend it. i'm currently looking for a natural clay vein but i want to be able to do something with what i already have. i recently re-discovered the pottery wheel and electric kiln that has lain dormant and forgotten in my family's basement. i'm also building a woodfire kiln in my backyard so some of my pieces can have that smokey black char look. i've also all ready built a crucible (out of a propane tank and concrete) for melting soft metals so i can cast my own pipe molds. I've named him Desmond The Destroyer (or Double D for short). i fired him up for the first time the other day. He's pretty awesome actually.

[Benzine]

I was given some "Found Clay" several years ago. It was a blue green clay, than when fired turns a golden yellow. I had to screen it quite a bit, to remove the debris. Before using it, I made some test tiles. The tiles fired fine, but the clay body was extremely weak. I could easily snap the quarter inch thick tile with my hands.

 

Also, a classmate of mine in college, brought a similar clay into the studio. It was bisque fired, and turned ou the same as my test years later. However, when fired to the glazing tempeature, at least Cone 6, it started to melt.

 

So apparently this specific type of found clay needs some additives, for it to be truely usable.

[neilestrick]

This is why we use clay bodies. It's rare that a single clay will function the way we need it to in the forming or firing. Chances are your clay will become part of a clay body recipe. But first you'll need to do firing and absorption tests to see what else you will need to add to it to make it useable.

[PuckGoodfellow]

Firing and absorption tests? Could you please post me a link to a tutorial? I'm not sure how to do those tests (accurately). My goal Is to have a finished product that I can say was made 100% by me (tools and clay included). I want to be a potter that doesn't need a ceramic supplier. I wish to replicate a medieval potter and do everything myself (if possible).

[Min]

http://digitalfire.com/4sight/tests/ A little bit of light reading regarding testing clay.

 

I wish you luck with your endeavors to replicate a medieval potter. You learn a lot about claybodies when you mix your own but to do it without any bought materials is going to be a real challenge. Even with bought materials it is a lot of hard dusty work. Maybe start reading up on slip glazes at the same time. You might find the clay you found would work better as part of a glaze rather than a claybody.

[neilestrick]

HERE is a recent thread about mixing your own clay. While it sounds romantic and all that, for most people it's best left to the professionals who can do it quickly and safely. The thing to remember about old timey potters is that they built their homes and potteries where the good clay was. They didn't just hope that there was some usable clay in their back yard. Some of those old potteries are still running today, but I doubt there are any that don't buy some raw materials from a ceramic materials supplier. Any ideas about what you're going to use for glaze? Are you going to build your own kiln with bricks you made yourself? There's a lot that goes into this if you really want it to be just like the old days.

 

That said, it is a worthwhile endeavor to learn how to process and test clay. You will learn a great deal, so it's worth doing. Just make sure you can do it safely, and don't get hung up on the 'purity' of the process.

[Stellaria]

You've got a good goal - one that I share (though I'm a good bit earlier - Iron Age.) Only I know that it'll be a LONG time before I get there, as just building the skills to get to the forms I want, even with well-behaved clay, takes an insane amount of practice.

I guess what I'm saying is - try not to think of it as working counter to your goal if you need to rely on a ceramics supplier while you build the skills you need to get you to your goal. There are many many little pieces to build up to it with, and it's okay to take them one at a time, using what you have available so you can focus on that baby step for the time being.

[Guest JBaymore]

Interesting and lofty goal.

 

Years and years and YEARS ago I did consulting work on the reconstruction of a true-to-period updraft collonial era earthenware bottle kiln for the living history musuem Old Sturbridge Village in Massachusetts.  It is a recreation of a colonial village.  Quite large.  It was a fascinating place... everyone was "in character" and in costume. Lots of traditional crafts..... raising sheep to get wool that was carded and spun into yarn, dyed with vegetable dyes, and so on.  Craft work and food sold to the visitors.  The pots they made in the pottery there were sold in the museum gift shop.

 

We used hand made bricks made by a local brick plant to build the large kiln (Turns out that the person who made those bricks -Kurt Heinzman- years later ended up taking pottery classes with me at NHIA!  We didn't know this common relationship until much later).  The bricks were hand struck and burned in ricks.

 

https://www.osv.org/pottery-shop-kiln

 

https://www.osv.org/gallery/pottery-kiln-firing

 

At the first firing there I remember that we need to make a sort of a metal flap for the air intakes to control the air flow better.  I had to send a runner across the village to contact the 'village smithy' across the museum grounds, and he had to then hand make the parts we needed to be totally "in period".  Took a good while to get that as we were firing.

 

Made you appreciate the conveniences of stuff like telephones and readily available manufactured goods.

 

The reason I relate this story here............ behind the scenes..... and behind closed doors....... there was a room full of modern electric kilns.  They also were using a non-raw-lead commercial glaze on the redware.   And while they had a publicly viewable clay pit and were doing tradional proccessing there, the earthenware clay that they really used for production was from Cutter Ceramics (the "Laguna" of that time ).  I think I also remember some electric wheels behind the scenes (been a LONG time.... memory fades).

 

Being totally traditional is tough.

 

best,

 

..................john

[PuckGoodfellow]

Wow!..  So much to respond to.

 

first off.. i would like to thank you for all the links! i need all the reading material i can get.

 

Second..  i would like to report that this second cleaning of my clay has helped A LOT! For the first time, my clay has passed the finger test!!! i'm super excited and rather hopeful.

 

As for my desire to replicate a medieval potter.. i know its going to take alot of work and time. So i'm not apposed to buying the items i need to get going now. i just want to be as close to "made all by me" as i can get right now.i'm doing what i can to be a self taught potter. i will reach my goal one day (hopefully sooner than later), but in the mean time,.. i expect i will fail more often than not (you can be promised i will be coming to y'all when that happens). i can't wait to test my clay. cross your fingers for me. if the clay turns out to be good than i can check something off my list of steps to reach my goal.

[PuckGoodfellow]

When i'm done building everything i want to build, i should be able to use modern AND dated ceramic methods. Once i get close to bisk firing my pieces (did i use the right term?) i'll start thinking about making a slip/glaze (still not sure what the difference is).

[Stellaria]

Bisque, but yes

[alabama]

 Right out of the ground it was like store bought clay. But when i washed it down to remove the aggregate i found that my screen wasn't fine enough and felt to sandy. i was left with clay that felt like sandpaper when it was rolled into a worm and dried. 

 

Hey,

You need to find another source of clay.  The initial on site clay tests are past or fail....  Not maybe. 

Your state should have a state geologist you can ask.  I've had good results visiting with brick company engineers ... You can learn alot

in a 10 minute chat with someone whose job it is to know about natural clays.  A thank you and a piece of pottery can get you another visit easier.

 

"Pottery Technology" is a good book to start out with natural clays and "Pre-Industrial Utensils- 1100 - 1800 AD"  is a good book to look at pottery

forms from the Iron Age thru the colonial period.

 

Whenever I find a new source of clay, I make a few beads out of it, let them dry and then see how much pressure it takes to pinch them into breaking.

Then I fire the beads, on a section of "mig wire" (found at Lowes) and pinch them again.  I have found that brittle clay beads make for brittle ceramic beads.

Oh, and don't use the mig wire in a kiln...it seems to melt and fuses things together..

Good Luck.

Alabama