Another Newbie Playing with Native Soil

[Genboomxer]

Hello Forum Folks,

One of the current projects I'm working on, now that I've acquired a little skill and knowledge, is to make some functional pieces from native soil.  This is something I've wanted to do since I was a kid playing in the fields where I grew up. 

I collected about 40 lbs of soil from an excavation site, slaked it into a slurry, and sieved it to ~40 mesh.  I dried it out on a hardibacker board, wedged it up and let it sit for a week. I netted about 20 lbs of a VERY sandy and short clay body.  I decided not to use or test it because of the sandy consistency.  I slaked it again and sieved it through 80 mesh which removed about 5 more lbs of fine sand.  Dried/wedged/waited a week as before.  This resulted in 15 lbs of a still short, but significantly more plastic, smelly clay body of a very dark, grey/green/brown color. It dries to a light grey/green. I'm guesstimating a 35% - 40% clay content???  Given the geology of the area I expected a very iron rich content. There are a lot of gold speckles when viewed in the sunlight that leads me to think Pyrite is plentiful. Maybe mica? The soil is from an alluvial plain about a mile from sandstone formations that was used for agriculture before heavy development in the middle of the last century. 

I wedged up a couple of chunks to see how it would perform on the wheel.  It gave little resistance and was remarkably soft and easy to throw. Like really thick peanut butter with sand in it. I decided I wasn't going to try and make anything too fine or thin because I was afraid of overworking it too quickly.  It produced little slip and soaked up a lot of water. I kept what slip I had and let it dry completely.  It is very hard to break and snaps apart without crumbling, if that means anything.  The 2 items I made had excellent green strength.  attaching a handle was an exercise in patience because of how short the clay turned out. I fully expected the handle to pop off in the bisque firing.  I also made a 10cm test tile to check shrinkage.  Dry shrink is ~6% or 7%.

Next, I decided that I couldn't leave well enough alone.  I combined equal parts ^10 B-Mix with the native clay, wedged it to homogeneity, and threw a small mug. This improved plasticity, was easier to throw, and demanded less water.  It behaved like a sandy B-mix and was a lot easier to put a handle on. I then did a ^06 bisque load in my electric kiln. I was expecting havoc and woe when I opened the kiln, but was pleased with the results so far. The native clay body fired to a deep terra cotta color Pictures do not do it justice. The blended clay body is a light salmon-y color.  The native has a bright ring when thumped; the blend a little less bright, even though it has thinner walls (prob. b/c of B-mix?) I have attached before and after photos for consideration.

Next I need to determine a suitable final firing temp to glaze and mature my experiments.  I also want to improve the workability and plasticity of the native clay body, but I'm not sure where to start.  I've read various methods for doing this, but it's like brewing: ask 10 brewers a question and you get 12 different answers. I'm sure that combining with the B-Mix was a quick and dirty impulse fraught with peril, but I can't help thinking it is a viable way to go.  What does this combination do in terms of glaze matching and maturation temp?  I think the native clay is a bit more straight forward in that it is terra cotta, so there are probably easier options to choose and test.  I'm thinking Spanish style of a white or red glaze (clear?).  I also want to use some of the processed native soil to glaze with.  I've seen it work on ^10 clay bodies, but not at ^6. 

Thanks in advance for the wisdom.

Dave

[Min]

Processing found "wild" clay has come up on the forum a number of times. This is one thread in particular that is worth reading. Checking for black coring (and amending the firing schedule if this happens) and checking for lime pops with vinegar are both a good ideas to start with. Look up the geological survey info for the area you got the clay from, it should give you some more info.

Are you looking to make a vitreous body including the found clay as part of the recipe or are you thinking of using it for lowfire earthenware? Do you have a test kiln to do some testing with, firing some samples to lowfire, mid and upper mid ranges to check melt / absorption / slumping etc? (firing samples in waster bowls)

[Genboomxer]

25 minutes ago, Min said:

Processing found "wild" clay has come up on the forum a number of times. This is one thread in particular that is worth reading. Checking for black coring (and amending the firing schedule if this happens) and checking for lime pops with vinegar are both a good ideas to start with. Look up the geological survey info for the area you got the clay from, it should give you some more info.

Are you looking to make a vitreous body including the found clay as part of the recipe or are you thinking of using it for lowfire earthenware? Do you have a test kiln to do some testing with, firing some samples to lowfire, mid and upper mid ranges to check melt / absorption / slumping etc? (firing samples in waster bowls)

Thanks for the link!  Turns out I've done most of what is suggested.  I will do  vinegar eat tonight because I know there was a lime industry uphill from my source and this is part of the geological makeup of the region. I have found more information about the source material (sandstone) than I have on the actual soil.  Any help for where to look for that is appreciated. 

I tested a bar of it and broke it in half.  No carbon coring at all.

I do not have a small test kiln per se, but I do have 2 kilns to work with, one ^6 electric. 3.3 cu ft,  and an ancient 7 cu ft gas kiln that can easily handle up to ^12, so I'm set there.  I am in the process of testing, but I'm really new to this and want to make sure I get all the info I can. Also, if someone has already gone down the same paths I'm on, maybe I don't have to do as much work. 

I want to explore all the possibilities with this wild clay.  What can I do with earthenware? How can I make it a clay body that matures at ^6 and/or ^10? All the stuff.

Thanks,

Dave

[liambesaw]

You can use your clay in a clay recipe once you figure out what type of clay it is.  Cone 6 clays contain clay, flux and Feldspar.  The flux and Feldspar help fuse and strengthen the clay, allowing it to mature or vitrify at a lower temperature. 

If your clay is short you can buy ball clay to mix with it, or try ball milling some of your clay as well and using some of that.  

You'll just have to do a lot of testing and adjusting as you go because no one else has done the work on this clay before you.

If you have a bureau of land management office around you, you can look up historical mineral mining maps and such. Some states have this available online as well through your local department of natural resources website, but as geological survey maps.  They're a lot harder to decipher in my opinion but provide better information about the actual geology of the area.  I'm just getting into amateur geology and find it all very interesting, especially in my area which has volcanic, block and fold mountains, big basalt columns and all sorts of great places to explore.  

[Genboomxer]

2 hours ago, liambesaw said:

You can use your clay in a clay recipe once you figure out what type of clay it is.  Cone 6 clays contain clay, flux and Feldspar.  The flux and Feldspar help fuse and strengthen the clay, allowing it to mature or vitrify at a lower temperature. 

If your clay is short you can buy ball clay to mix with it, or try ball milling some of your clay as well and using some of that.  

You'll just have to do a lot of testing and adjusting as you go because no one else has done the work on this clay before you.

If you have a bureau of land management office around you, you can look up historical mineral mining maps and such. Some states have this available online as well through your local department of natural resources website, but as geological survey maps.  They're a lot harder to decipher in my opinion but provide better information about the actual geology of the area.  I'm just getting into amateur geology and find it all very interesting, especially in my area which has volcanic, block and fold mountains, big basalt columns and all sorts of great places to explore.  

I guess I'm not sure what you mean by "what type of clay it is". I'm guessing it's a type of high iron, terra cotta earthenware.  The soil is from the west San Fernando Valley of Los Angeles, in the shadow of the sandstone bluffs where I grew up. I know the S. F. Mission made its roof and floor tiles, as well as some tableware and storage ware from locally sourced clay, so this keeps me hopeful it is viable with the right treatment.

I assumed I would have to do extensive testing because I haven't found a lot of other folks doing it online, and I have a tendency to do weird things few people do for my own creatively nutty reasons. Commercially available clay is great, but I want to add a personal, unique twist to my work if I can. I wasn't sure I would get this far, so I'm excited to do the work. 

I purchased some ball clay (OM-4) and feldspars for mixing my own glazes (another new experience of experimentation) so I will start to play with those ingredients and see where I get.  It would help to have a methodology for adding such materials in the right ratios.  It's not a deal breaker if I can't make a stoneware out of it, but I do want a durable and versatile local clay body for functional wares. A ball mill is not a budget priority so I will just have to work around it. Although I have a desire to see if the nearby sandstone can be used as a glaze ingredient. I did find a report on the sandstone. It is composed of 54% granite; 45% feldspar, cemented with limonite (iron ore).  So who knows I might eventually get a ball mill (maybe a large rock tumbler? ) for that and see what happens. I've been trying to decipher the survey maps myself.  I've read several, but they're pretty general for the area; no actual analysis of the specific soil, just suitability for farming and erosion characteristics.  "Sandy loam" is not helpful. Mineral content of the soil is still eluding me, but I hunt on.   

Edit: P.S. - Any insights regarding the 50/50 blend with ^10 B-Mix?  Does this theoretically up the maturation temp? I have only found one other person who has done this, and fired it to ^6 with success, but they haven't done any more than that.

Thanks,

Dave

 

[liambesaw]

By what type of clay I mean there's clays with different ratios of silica and alumina so some melt or mature earlier than others.  You'll just have to fire samples to different cones and see what happens or have it sent for testing.

Testing it would be good so you can incorporate it into glaze calculation and know exactly what is in it.  I'm assuming this would make it easier to determine a good clay recipe as well.

[Genboomxer]

9 hours ago, liambesaw said:

By what type of clay I mean there's clays with different ratios of silica and alumina so some melt or mature earlier than others.  You'll just have to fire samples to different cones and see what happens or have it sent for testing.

Testing it would be good so you can incorporate it into glaze calculation and know exactly what is in it.  I'm assuming this would make it easier to determine a good clay recipe as well.

Testing makes a lot of sense. Do you have a suggested lab?

[liambesaw]

15 minutes ago, Genboomxer said:

Testing makes a lot of sense. Do you have a suggested lab?

I don't but paging @glazenerd might help!

[Min]

@GreyBird dug clay along the Hudson River and had a sample analyzed, you could message her and ask where she got it done. This is the thread showing the process etc. for GreyBirds found clay. There is also a lot of good info in that thread from @glazenerd .

Found clay is often earthenware type clay so adding the ^10 B-mix would definitely raise the maturation temperature but it doesn't necessarily mean the clay would be okay with just that addition. Assuming what you have is a lowfire red clay then by adding the ^10 clay is in effect no different than when RedArt (lowfire red clay) is added to bodies to introduce iron into them, still have to balance the recipe out.  Have a look at the recipes in the Grinding Room from Alfred. Some of the materials used are no longer available but it will give you an idea of what you might need to add to your clay to complete it. It's going to be a process of trial and error but if you get an analysis done it will make the job a lot easier.

 

[Genboomxer]

25 minutes ago, Min said:

@GreyBird dug clay along the Hudson River and had a sample analyzed, you could message her and ask where she got it done. This is the thread showing the process etc. for GreyBirds found clay. There is also a lot of good info in that thread from @glazenerd .

Found clay is often earthenware type clay so adding the ^10 B-mix would definitely raise the maturation temperature but it doesn't necessarily mean the clay would be okay with just that addition. Assuming what you have is a lowfire red clay then by adding the ^10 clay is in effect no different than when RedArt (lowfire red clay) is added to bodies to introduce iron into them, still have to balance the recipe out.  Have a look at the recipes in the Grinding Room from Alfred. Some of the materials used are no longer available but it will give you an idea of what you might need to add to your clay to complete it. It's going to be a process of trial and error but if you get an analysis done it will make the job a lot easier.

 

Thank you for the links!  I looked for similar topics here but sometimes if you don't use the right key word it doesn't come up.

I did drop a piece of the fired clay into vinegar and it only fizzed for a second, so I'm interpreting that to mean I'm good on lime distribution. I am working on more test tiles today, and buying more witness cones for the varying temps I plan to test at. I think analysis will also help in that I should be focusing on practicing with what I have rather than playing with a theory. But I love learning new things.

So much appreciation for the wisdom and guidance!

[Min]

30 minutes ago, Genboomxer said:

I did drop a piece of the fired clay into vinegar and it only fizzed for a second

Try it with some unfired dry clay.

[glazenerd]

Gen:

Gold specks possible pyrite: but not mica- mica would be glassy or white. Pyrite is FeS (sulfur) and judging by your result with 50 local 50 B-mix: you have in excess of 8% iron content. The only issue that makes me doubt pyrite is the dried greenish color: hematite in the presence of calcium will present greenish.  The simple test to determine that: iron disulfide (pyrite) will go brown at cone 6- hematite will keep a deep red tint.  Alluvial soil is fine grained- sub micron and lower in alumina. If pyrite, doubt you can fire past cone 1-2 without pyroplastic issues. If hematite: then it should handle cone 6 because hematite and magnetite clay runs between 20-24% alumina- iron disulfide runs 15-17%. The test is simple: just put a button of you clay on a tile, scrap whatever and cook it to cone 6. Brown- iron disulfide- low fire. Deep red- hematite.

Plasticity- your sample has high sand content which is "tempering" the clay- not the same as plasticity. Tempering comes from the brick industry- used to produce malleability, but not plasticity. (They do not want high shrink values). Plasticity- start with 20% OM4. EX. 200 grams OM4 per 1000 grams local clay. You are hand mixing I assume? If so, it will take 3-5 days before full plasticity will develop. Overdo the plasticizer then you will have the opposite problem of clay fatigue- slumping-folding. 

Burn a sample to cone 6-  confirm what the iron source is: then address formula- cone value.

Nerd

[Genboomxer]

10 hours ago, Min said:

Try it with some unfired dry clay.

Thanks.  Very little and brief fizz.  

[traceyphillips]

On 9/18/2019 at 11:19 PM, Genboomxer said:

Hello Forum Folks,

One of the current projects I'm working on, now that I've acquired a little skill and knowledge, is to make some functional pieces from native soil.  This is something I've wanted to do since I was a kid playing in the fields where I grew up. 

I collected about 40 lbs of soil from an excavation site, slaked it into a slurry, and sieved it to ~40 mesh.  I dried it out on a hardibacker board, wedged it up and let it sit for a week. I netted about 20 lbs of a VERY sandy and short clay body.  I decided not to use or test it because of the sandy consistency.  I slaked it again and sieved it through 80 mesh which removed about 5 more lbs of fine sand.  Dried/wedged/waited a week as before.  This resulted in 15 lbs of a still short, but significantly more plastic, smelly clay body of a very dark, grey/green/brown color. It dries to a light grey/green. I'm guesstimating a 35% - 40% clay content???  Given the geology of the area I expected a very iron rich content. There are a lot of gold speckles when viewed in the sunlight that leads me to think Pyrite is plentiful. Maybe mica? The soil is from an alluvial plain about a mile from sandstone formations that was used for agriculture before heavy development in the middle of the last century. 

I wedged up a couple of chunks to see how it would perform on the wheel.  It gave little resistance and was remarkably soft and easy to throw. Like really thick peanut butter with sand in it. I decided I wasn't going to try and make anything too fine or thin because I was afraid of overworking it too quickly.  It produced little slip and soaked up a lot of water. I kept what slip I had and let it dry completely.  It is very hard to break and snaps apart without crumbling, if that means anything.  The 2 items I made had excellent green strength.  attaching a handle was an exercise in patience because of how short the clay turned out. I fully expected the handle to pop off in the bisque firing.  I also made a 10cm test tile to check shrinkage.  Dry shrink is ~6% or 7%.

Next, I decided that I couldn't leave well enough alone.  I combined equal parts ^10 B-Mix with the native clay, wedged it to homogeneity, and threw a small mug. This improved plasticity, was easier to throw, and demanded less water.  It behaved like a sandy B-mix and was a lot easier to put a handle on. I then did a ^06 bisque load in my electric kiln. I was expecting havoc and woe when I opened the kiln, but was pleased with the results so far. The native clay body fired to a deep terra cotta color Pictures do not do it justice. The blended clay body is a light salmon-y color.  The native has a bright ring when thumped; the blend a little less bright, even though it has thinner walls (prob. b/c of B-mix?) I have attached before and after photos for consideration.

Next I need to determine a suitable final firing temp to glaze and mature my experiments.  I also want to improve the workability and plasticity of the native clay body, but I'm not sure where to start.  I've read various methods for doing this, but it's like brewing: ask 10 brewers a question and you get 12 different answers. I'm sure that combining with the B-Mix was a quick and dirty impulse fraught with peril, but I can't help thinking it is a viable way to go.  What does this combination do in terms of glaze matching and maturation temp?  I think the native clay is a bit more straight forward in that it is terra cotta, so there are probably easier options to choose and test.  I'm thinking Spanish style of a white or red glaze (clear?).  I also want to use some of the processed native soil to glaze with.  I've seen it work on ^10 clay bodies, but not at ^6. 

Thanks in advance for the wisdom.

Dave

Great job! How long have you been doing this for?

[Callie Beller Diesel]

The week of August 12-16 (you can scroll down to the correct dates) Naomi Hunt of Bandana Pottery did a very informative series of Instagram posts on how they process their wild clay, and what they do to get it workable. (We can hope she puts it in a more permanent form on her website, but this is what we have at the moment.)  

You do not need an Instagram account to check out their feed. Click on the thumbnails to view the posts.

Instagram.com/bandanapottery

 

[Genboomxer]

3 hours ago, traceyphillips said:

Great job! How long have you been doing this for?

Thank you!

I started this project about 5 months ago, but I've only recently had the time and means to fire and test at home.

[Genboomxer]

3 hours ago, Callie Beller Diesel said:

The week of August 12-16 (you can scroll down to the correct dates) Naomi Hunt of Bandana Pottery did a very informative series of Instagram posts on how they process their wild clay, and what they do to get it workable. (We can hope she puts it in a more permanent form on her website, but this is what we have at the moment.)  

You do not need an Instagram account to check out their feed. Click on the thumbnails to view the posts.

Instagram.com/bandanapottery

 

Thank you for sharing!  The more I see of NC the more I understand why it is such a hub for potters. Three different varieties of clay within a stone's throw? Amazing. And their work is elegant.

P.S.  I took a look at your website and I really like your work.  I especially like the Distress Cetre mugs, and the motivation and humanity that inspired them. 

[Genboomxer]

On 9/19/2019 at 3:10 PM, glazenerd said:

Gen:

Gold specks possible pyrite: but not mica- mica would be glassy or white. Pyrite is FeS (sulfur) and judging by your result with 50 local 50 B-mix: you have in excess of 8% iron content. The only issue that makes me doubt pyrite is the dried greenish color: hematite in the presence of calcium will present greenish.  The simple test to determine that: iron disulfide (pyrite) will go brown at cone 6- hematite will keep a deep red tint.  Alluvial soil is fine grained- sub micron and lower in alumina. If pyrite, doubt you can fire past cone 1-2 without pyroplastic issues. If hematite: then it should handle cone 6 because hematite and magnetite clay runs between 20-24% alumina- iron disulfide runs 15-17%. The test is simple: just put a button of you clay on a tile, scrap whatever and cook it to cone 6. Brown- iron disulfide- low fire. Deep red- hematite.

Plasticity- your sample has high sand content which is "tempering" the clay- not the same as plasticity. Tempering comes from the brick industry- used to produce malleability, but not plasticity. (They do not want high shrink values). Plasticity- start with 20% OM4. EX. 200 grams OM4 per 1000 grams local clay. You are hand mixing I assume? If so, it will take 3-5 days before full plasticity will develop. Overdo the plasticizer then you will have the opposite problem of clay fatigue- slumping-folding. 

Burn a sample to cone 6-  confirm what the iron source is: then address formula- cone value.

Nerd

Hello again Nerd!

I finally got around to firing a sample of my project to ^6.  In the attached photo I have 2 samples. Top sample is native soil (I call it CPM) mixed 50/50 with ^10 b-mix. I'm pleased with the results so far regarding texture and color.  Shrinkage is ~12%. I also glazed a small mug made of the same 50/50 clay body with a home-mixed celadon (Britt Basic) and it turned out quite nice. I does appear to have crazed though.

The bottom sample is the native by itself fired to ^6.  Dark brown and glassy. It broke during firing. Probably during cool-down? It isn't brittle as I've tried to break it by hand and it's quite strong.  I think this answers the iron / pyrite content question? 

Thanks again for your insights!

[glazenerd]

Gen:

In the USA; iron bearing clay sources iron disulfide (most common, hematite, or magnetite. Iron disulfide is easy to spot because it fires into the brown range at cone 6; along with the typical bloating, blistering and black coring commonly associated with it. Hematite and magnetite will keep its classic "Terra Cotta" color, deepening into reds, reddish brown as you fire over cone 6.  The green native clay you show is common down in the Carolinas; the green cast coming from chlorite materials. The other issue you will find in conjunction with iron; is the alumina content. Alumina is obviously refractory and plays a key role in maturation temps. Low alumina (15-16%)will become molten at cone 04. As the alumina increases (20-24%) it tolerates more heat (cone 5-6) and 26-30% cone 10. Alumina levels also play a role in color development as well. Native clays with higher alumina content and iron bearing will keep its color to higher temps as well. Fired buff color 2-3% iron, Terra Cotta 4-5% iron, and you can reds, purples- 6-8% iron (magnetite or hematite only) with higher titanium levels.

Tom. Do a search on Facebook for "Clay Tech".. lots of clay info there.

[Genboomxer]

4 minutes ago, glazenerd said:

Gen:

In the USA; iron bearing clay sources iron disulfide (most common, hematite, or magnetite. Iron disulfide is easy to spot because it fires into the brown range at cone 6; along with the typical bloating, blistering and black coring commonly associated with it. Hematite and magnetite will keep its classic "Terra Cotta" color, deepening into reds, reddish brown as you fire over cone 6.  The green native clay you show is common down in the Carolinas; the green cast coming from chlorite materials. The other issue you will find in conjunction with iron; is the alumina content. Alumina is obviously refractory and plays a key role in maturation temps. Low alumina (15-16%)will become molten at cone 04. As the alumina increases (20-24%) it tolerates more heat (cone 5-6) and 26-30% cone 10. Alumina levels also play a role in color development as well. Native clays with higher alumina content and iron bearing will keep its color to higher temps as well. Fired buff color 2-3% iron, Terra Cotta 4-5% iron, and you can reds, purples- 6-8% iron (magnetite or hematite only) with higher titanium levels.

Tom. Do a search on Facebook for "Clay Tech".. lots of clay info there.

This soil is from the west San Fernando Valley in So CA.  What can I infer from the result I go?  No bloating or black coring evident in the samples.  I'm guessing I will need to stick to low-fire, majolica or non-functional projects?

Thanks again for the knowledge.

[glazenerd]

Gen- I will add SoCal to my list. From the color response you are dealing with iron disulfide. I would fire to cone 3, and check color response: then fire to cone 1- and check it again. I will assume you are after classic Terra Cotta. Once you determine the highest cone value verses color; you can then build flux additions around that cone to lower absorption. 

T