glazenerd

Picture below has been cropped to fit format: actual clay size is 7” x 4” x 4”. Sample was saw cut and wetted to illustrate layers/ color/ and grain. Sample was flipped upside down to capture color variations. The orange/gold color on top is actually the bottom of the sample.
A wild clay sample can tell you a lot just by looking at it. Obviously this is a sedimentary clay because it has three distinct layers and colors. The bottom layer is thin, and is noted by the cleavage crack at the bottom left corner. The top layer is granular and light orange/gold in color, which denotes the presence of iron disulfide (iron). This sample of iron disulfide is light in color, which means total iron content is in the 3-4% range. As the percentage of iron goes up; the color will become deeper and deeper. Naturally occurring magnetite (iron) usually presents medium to dark gray in clay color. Naturally occurring hematite will present light to medium “reddish” in color, with no goldish hue. Iron disulfide typically has a gold cast because the iron is oxidizing (rust), whereas hematite is not subject to this natural process.
The middle layer is dark brown ball clay which typically indicates the presence of inorganic sulfides from lignite coal particles. Lighter brown color means less inorganic material, and darker brown means more. The exception to that rule is organic particles (humus). If your sample was taken from a heavily vegetated area; then the level of organic (humus) will be higher, which like wise will create a dark brown appearance. How can you tell if its organic or inorganic? First, the collection site: open fields or valleys will have less organic material, and heavily vegetated areas will have more. Secondly, a very simple test: take a small 1/4 cup powdered clay sample and add a a bit of water at a time until it forms a pliable ball. Does not have to be all nice and neat; just pliable. If it is sticky or gummy feeling; organics. If you can roll it between your hands without it sticking or smearing; it is inorganic. Yes, there are exceptions were a sample can have both inorganic and organic materials.
Besides the obvious large particles of shale; did you notice the smaller nodules? There seems to be a heavy population of them in this sample; which means the middle layer has a higher percentage of 20-60 mesh particles. Bad thing? No, it can be used for non-functional, large format pieces. If you are going to make cups and bowls, then these larger particles have to come out. Wet processing will allow the large particles to settle out quickly, or dry processing will require a 60-80 mesh screen. This sample was found in an open eroded ditch in a field, so the color is most likely from inorganic sulfide. The presence of these sulfides also indicates a coal seam is nearby: which I happen to know is correct because of the numerous coal mines located locally back in the late 1800’s. This knowledge also helps determine the plasticity of ball clay located next to coal seams; typically they are more plastic. 
The bottom (thin layer) is free from large particles, and because this is a sedimentary sample; also means it is finer and more plastic. As with all clay sediments; larger particles drop out first, and smaller particles drop out last. Remember, this sample was photographed upside down to capture color variance. So the thin layer on the bottom, is actually the top of the sample. Can you field test plasticity? yes. Make a 1/4 cup of the middle layer, and a 1/4 cup of the bottom layer to start. If you have a scale, you can accurately measure what you add to each sample to create a pliable ball. If no scale; add 1 teaspoon, add a second, and once it begins to form a ball, then add 1/2 teaspoon until it becomes a pliable ball that does not crumble, nor overly wet and sticky. Low plasticity clay requires less water to form a pliable ball, and a high plasticity clay requires more water for the same. Exact? no- but will give you some general sense and direction.
Tom
 

Picture below has been cropped to fit format: actual clay size is 7” x 4” x 4”. Sample was saw cut and wetted to illustrate layers/ color/ and grain. Sample was flipped upside down to capture color variations. The orange/gold color on top is actually the bottom of the sample.
A wild clay sample can tell you a lot just by looking at it. Obviously this is a sedimentary clay because it has three distinct layers and colors. The bottom layer is thin, and is noted by the cleavage crack at the bottom left corner. The top layer is granular and light orange/gold in color, which denotes the presence of iron disulfide (iron). This sample of iron disulfide is light in color, which means total iron content is in the 3-4% range. As the percentage of iron goes up; the color will become deeper and deeper. Naturally occurring magnetite (iron) usually presents medium to dark gray in clay color. Naturally occurring hematite will present light to medium “reddish” in color, with no goldish hue. Iron disulfide typically has a gold cast because the iron is oxidizing (rust), whereas hematite is not subject to this natural process.
The middle layer is dark brown ball clay which typically indicates the presence of inorganic sulfides from lignite coal particles. Lighter brown color means less inorganic material, and darker brown means more. The exception to that rule is organic particles (humus). If your sample was taken from a heavily vegetated area; then the level of organic (humus) will be higher, which like wise will create a dark brown appearance. How can you tell if its organic or inorganic? First, the collection site: open fields or valleys will have less organic material, and heavily vegetated areas will have more. Secondly, a very simple test: take a small 1/4 cup powdered clay sample and add a a bit of water at a time until it forms a pliable ball. Does not have to be all nice and neat; just pliable. If it is sticky or gummy feeling; organics. If you can roll it between your hands without it sticking or smearing; it is inorganic. Yes, there are exceptions were a sample can have both inorganic and organic materials.
Besides the obvious large particles of shale; did you notice the smaller nodules? There seems to be a heavy population of them in this sample; which means the middle layer has a higher percentage of 20-60 mesh particles. Bad thing? No, it can be used for non-functional, large format pieces. If you are going to make cups and bowls, then these larger particles have to come out. Wet processing will allow the large particles to settle out quickly, or dry processing will require a 60-80 mesh screen. This sample was found in an open eroded ditch in a field, so the color is most likely from inorganic sulfide. The presence of these sulfides also indicates a coal seam is nearby: which I happen to know is correct because of the numerous coal mines located locally back in the late 1800’s. This knowledge also helps determine the plasticity of ball clay located next to coal seams; typically they are more plastic. 
The bottom (thin layer) is free from large particles, and because this is a sedimentary sample; also means it is finer and more plastic. As with all clay sediments; larger particles drop out first, and smaller particles drop out last. Remember, this sample was photographed upside down to capture color variance. So the thin layer on the bottom, is actually the top of the sample. Can you field test plasticity? yes. Make a 1/4 cup of the middle layer, and a 1/4 cup of the bottom layer to start. If you have a scale, you can accurately measure what you add to each sample to create a pliable ball. If no scale; add 1 teaspoon, add a second, and once it begins to form a ball, then add 1/2 teaspoon until it becomes a pliable ball that does not crumble, nor overly wet and sticky. Low plasticity clay requires less water to form a pliable ball, and a high plasticity clay requires more water for the same. Exact? no- but will give you some general sense and direction.
Tom
 

When reviewing clay specs: the alumina content will predict plasticity. The lower the alumina content; the more plastic the clay will be. Example: kaolin is 37% alumina, and nearly non-plastic. Larger grain (micron) ball clays have 27-31% alumina, and typically rated as medium plasticity. Fine particle (sub-micron) ball clays with high plasticity run 24-27% alumina. As alumina levels drop, plasticity increases: bentonite (very high plastiity) has 20% alumina. BentoneMA (even more plastic than bentonite) is highly processed hectorite with less than 2% alumina. Particle size also effects plasticity: fire clays have a percentage of large (20-80) mesh particles that lower plasticity; even though it has lower alumina. High plasticity ball clays are under 1 micron particle size; or sub-micron particles. Example: Kaolin run 2-20 microns typically; which also plays into its non-plastic rating. OM4 ball clay runs 0.67 microns and is medium plasticity. CMC ball clay is just below 0.50 microns and is rated high plasticity. I use Taylor ball clay (not available commercially) that is 0.27 microns and extremely plastic.
When formulating: plasticity ratings matter. For example: a common formulation basis is 25% kaolin, 25% ball clay, 25% silica, and 25% feldspar (cone 10)  25% OM4 ball clay will create workable plasticity. If you changed that 25% to CMC ball clay: the body would absorb water rapidly and collapse quickly on the wheel because CMC is much more plastic than OM4. Let me express this another way: 8% of my Taylor ball clay will produce more plasticity than 25% of OM4. So you have to understand that parameter when formulating. Remember: high plasticity equals high water absorption. Randomly switching ball clays in equal additions (25% OM4 verses 25% CMC) will turn a plastic clay into a “fat” clay quickly. 
Alumina will predict plasticity in most all cases. Exceptions: as mentioned, larger particle sizes will lower plasticity even when alumina is lower. 2. Higher calcium content will increase plasticity when alumina content is higher because calcium creates isomorphic substitution (don’t ask) at a higher rate than sodium or potassium. 
Fireclays have higher inorganic sulfide levels which equate to higher LOI at 1750F. Inorganic sulfides = lignite coal particles.
Tom

When reviewing clay specs: the alumina content will predict plasticity. The lower the alumina content; the more plastic the clay will be. Example: kaolin is 37% alumina, and nearly non-plastic. Larger grain (micron) ball clays have 27-31% alumina, and typically rated as medium plasticity. Fine particle (sub-micron) ball clays with high plasticity run 24-27% alumina. As alumina levels drop, plasticity increases: bentonite (very high plastiity) has 20% alumina. BentoneMA (even more plastic than bentonite) is highly processed hectorite with less than 2% alumina. Particle size also effects plasticity: fire clays have a percentage of large (20-80) mesh particles that lower plasticity; even though it has lower alumina. High plasticity ball clays are under 1 micron particle size; or sub-micron particles. Example: Kaolin run 2-20 microns typically; which also plays into its non-plastic rating. OM4 ball clay runs 0.67 microns and is medium plasticity. CMC ball clay is just below 0.50 microns and is rated high plasticity. I use Taylor ball clay (not available commercially) that is 0.27 microns and extremely plastic.
When formulating: plasticity ratings matter. For example: a common formulation basis is 25% kaolin, 25% ball clay, 25% silica, and 25% feldspar (cone 10)  25% OM4 ball clay will create workable plasticity. If you changed that 25% to CMC ball clay: the body would absorb water rapidly and collapse quickly on the wheel because CMC is much more plastic than OM4. Let me express this another way: 8% of my Taylor ball clay will produce more plasticity than 25% of OM4. So you have to understand that parameter when formulating. Remember: high plasticity equals high water absorption. Randomly switching ball clays in equal additions (25% OM4 verses 25% CMC) will turn a plastic clay into a “fat” clay quickly. 
Alumina will predict plasticity in most all cases. Exceptions: as mentioned, larger particle sizes will lower plasticity even when alumina is lower. 2. Higher calcium content will increase plasticity when alumina content is higher because calcium creates isomorphic substitution (don’t ask) at a higher rate than sodium or potassium. 
Fireclays have higher inorganic sulfide levels which equate to higher LOI at 1750F. Inorganic sulfides = lignite coal particles.
Tom

Besides the obvious issue with firing large slabs flat (dunting), the other issue is uneven heat. The side exposed to ambient kiln temperature can vary to the temperature under the slab in direct contact with the shelf; further adding to the warp issue. I have fire porcelain slabs up to 30” square by bisq firing them on edge. Use tile setters as shown, or prop them up using other wares. 
Tom

Besides the obvious issue with firing large slabs flat (dunting), the other issue is uneven heat. The side exposed to ambient kiln temperature can vary to the temperature under the slab in direct contact with the shelf; further adding to the warp issue. I have fire porcelain slabs up to 30” square by bisq firing them on edge. Use tile setters as shown, or prop them up using other wares. 
Tom

Kelly
Can tell you a fair amount just from the description. chocolately color is magnetite; which also presents dark grey/ with blue/green (calcium) in the wild. Pyroplasticity in the lower range 04- 1 indicates low alumina, not high flux content. From my testing; alumina is in the 16% range, which also means the silica is elevated into the 70+% range. Potters automatically assume pyroplasticity in clay is caused by high flux content due to their familiarity with glaze. Glaze is in direct contact with ambient kiln temp, while that same temp can take 30 plus minutes to penetrate a clay wall- hence the hold time often used in firings. Most glazes incorporate 200-325 mesh material, while clay often has 40-120 mesh materials.  Testing alumina is fairly simple: just add 20% kaolin (37% alumina) to your wild clay and fire it again to the known slump temp. You will know in a heartbeat if its alumina issues. 
Years ago, i developed a split LOI test that I sent to Tony Hansen and Ron Roy. From Tony’s email, I assume at some point he took it for a test drive. If you want to give it a shot; I will send a link to my private clay page. 
Tom 

Kelly
Can tell you a fair amount just from the description. chocolately color is magnetite; which also presents dark grey/ with blue/green (calcium) in the wild. Pyroplasticity in the lower range 04- 1 indicates low alumina, not high flux content. From my testing; alumina is in the 16% range, which also means the silica is elevated into the 70+% range. Potters automatically assume pyroplasticity in clay is caused by high flux content due to their familiarity with glaze. Glaze is in direct contact with ambient kiln temp, while that same temp can take 30 plus minutes to penetrate a clay wall- hence the hold time often used in firings. Most glazes incorporate 200-325 mesh material, while clay often has 40-120 mesh materials.  Testing alumina is fairly simple: just add 20% kaolin (37% alumina) to your wild clay and fire it again to the known slump temp. You will know in a heartbeat if its alumina issues. 
Years ago, i developed a split LOI test that I sent to Tony Hansen and Ron Roy. From Tony’s email, I assume at some point he took it for a test drive. If you want to give it a shot; I will send a link to my private clay page. 
Tom 

Kelly
Can tell you a fair amount just from the description. chocolately color is magnetite; which also presents dark grey/ with blue/green (calcium) in the wild. Pyroplasticity in the lower range 04- 1 indicates low alumina, not high flux content. From my testing; alumina is in the 16% range, which also means the silica is elevated into the 70+% range. Potters automatically assume pyroplasticity in clay is caused by high flux content due to their familiarity with glaze. Glaze is in direct contact with ambient kiln temp, while that same temp can take 30 plus minutes to penetrate a clay wall- hence the hold time often used in firings. Most glazes incorporate 200-325 mesh material, while clay often has 40-120 mesh materials.  Testing alumina is fairly simple: just add 20% kaolin (37% alumina) to your wild clay and fire it again to the known slump temp. You will know in a heartbeat if its alumina issues. 
Years ago, i developed a split LOI test that I sent to Tony Hansen and Ron Roy. From Tony’s email, I assume at some point he took it for a test drive. If you want to give it a shot; I will send a link to my private clay page. 
Tom 

Well said. Brick making relies on malleability, not plasticity. Seen a few million bricks in my 50 year carpenter career, and pending the clay mine; chunks up to 3/8” is not uncommon. Potters avoid black coring, whereas the brick industry utilizes it to produce low absorption. Brick is fired in the 06-04 range mostly, at a fairly high speed with the intent to produce black glass (coring). It all comes down to the original poster willing to do that much work. Just so you know; 7 standard size bricks equal 1 square foot. 
Tom

Well said. Brick making relies on malleability, not plasticity. Seen a few million bricks in my 50 year carpenter career, and pending the clay mine; chunks up to 3/8” is not uncommon. Potters avoid black coring, whereas the brick industry utilizes it to produce low absorption. Brick is fired in the 06-04 range mostly, at a fairly high speed with the intent to produce black glass (coring). It all comes down to the original poster willing to do that much work. Just so you know; 7 standard size bricks equal 1 square foot. 
Tom

Well said. Brick making relies on malleability, not plasticity. Seen a few million bricks in my 50 year carpenter career, and pending the clay mine; chunks up to 3/8” is not uncommon. Potters avoid black coring, whereas the brick industry utilizes it to produce low absorption. Brick is fired in the 06-04 range mostly, at a fairly high speed with the intent to produce black glass (coring). It all comes down to the original poster willing to do that much work. Just so you know; 7 standard size bricks equal 1 square foot. 
Tom

Well said. Brick making relies on malleability, not plasticity. Seen a few million bricks in my 50 year carpenter career, and pending the clay mine; chunks up to 3/8” is not uncommon. Potters avoid black coring, whereas the brick industry utilizes it to produce low absorption. Brick is fired in the 06-04 range mostly, at a fairly high speed with the intent to produce black glass (coring). It all comes down to the original poster willing to do that much work. Just so you know; 7 standard size bricks equal 1 square foot. 
Tom

One more thing, bricks are not pots. Stuff that would disqualify a clay for pottery may not for bricks. You’re looking for enough clay to hold it together, and it to stay together until it’s fired. Additions of fibrous material are common to brick making. Critical for adobe blocks. Aggregates much too large for pottery clay are also  common in brick clay. Plasticity is a wholly different issue for potters than brick makers. Your first tasks:
1. Can it be formed into a brick?
2. What are its fired characteristics at various cones? 

To start, make a small tile by hand (nothing fancy) and let it dry> did it crack while drying? Next fire it to cone 06? what color? did it crack? The first step in wild clay processing is to see if its worth working with. Get past the simple test. Next, dry process 1 pound by pulverizing chunks into powder. Work it through a strainer ( window screen, kitchen strainer, etc) and repeat the above process to check how it dries and how it fires. >>outside with a mask<< How much sand? After you dry process one pound; put a 1/4 cup of dry clay in 3/4 cup of water in a clear glass container, and stir/shake well.. The sand will settle out very quickly. The thicker the sediment layer on the bottom equals the amount of sand present. 15-20% sand is acceptable, alot of brick makers add and for malleability. Commonly called temper in the wild clay circles. Run these simple tests and get back to me once you have. 
Note: worked with two potteries in India that used subtropical laterite clay. After the monsoon season; laterite can be found in smaller streams up to 4-5 feet thick. They simply dig it out and put it into brick molds. Sub-tropical laterite is the most common clay in India with over 40% combined alumina/.iron content. It dries so hard that it is often not fired before using as a brick. A property known as cementing occurs that makes unfired brick almost as hard as fired brick in the States. 
Tom
 

Adding vinegar is an experiment to check for high alkalinity from salt. As I noted, if the Ph rises above 9.8, then a property known as cementing occurs. Cementing is extreme flocculation. If this experiment does not change any of the working properties; then you go back to looking at common issues such as silt or particle size. 
T

The working properties you describe suggest you have found wild kaolin, not earthenware. How about a very fast experiment: mix 1/3 of your commercial stoneware with 2/3 wild clay. Let it sit 4-5 days, and work with it again. If indeed it is kaolin; it is “fiddly” because kaolin is a larger particle clay with very little naturally occurring plasticity. Another indication it is kaolin: did it dry in about half the time as your stoneware? 
Tom

All information is sourced from PhD’s (Ceramic Engineering) that I collected over the years.
 

Orton — auto-correct once again. 

Rob:
You have magnetite (iron) bearing clay; somewhere in the 7-9% total iron content range. Classic terra cotta at cone 04, and chocolate brown at 6+. You will get red in thin layers, but if you get it too thick- orange/tan to brown as it gets thicker. Must be slow moving waters for that distribution of very fine particles; bit unusual. Also surprised there is no plasticity; Ord humus (organics) commonly found in lake/river/stream collection areas. NY State also has an unique variety of smecites; which is also highly plastic. From everything I have seen and read; 1-2 micron particle sizes 
The note of interest to me: “stays suspended” and “no plasticity.” Those two do not fit clay chemistry with one exception: high calcium content. Calcium will keep fine particles suspended when “common plasticizers” are absent. The melted blob at cone 6+ indicates total alumina content is 15% or less. If you want to work with it, I will post some fixes. If not, enjoy the wild clay adventure.
Tom

All information is sourced from PhD’s (Ceramic Engineering) that I collected over the years.
 

Still looking for Orion work; lost a lot of info when my old laptop took a dirt nap. Brownell did similar studies as well. 

Edward Orion, Jr. (yes, the cone guy) did the early studies on inorganic burnout back in 1906-1910 period. In reading his abstract: he cites inorganic burnout between 1250 to 1750F.
T

Edward Orion, Jr. (yes, the cone guy) did the early studies on inorganic burnout back in 1906-1910 period. In reading his abstract: he cites inorganic burnout between 1250 to 1750F.
T

Rob:
You have magnetite (iron) bearing clay; somewhere in the 7-9% total iron content range. Classic terra cotta at cone 04, and chocolate brown at 6+. You will get red in thin layers, but if you get it too thick- orange/tan to brown as it gets thicker. Must be slow moving waters for that distribution of very fine particles; bit unusual. Also surprised there is no plasticity; Ord humus (organics) commonly found in lake/river/stream collection areas. NY State also has an unique variety of smecites; which is also highly plastic. From everything I have seen and read; 1-2 micron particle sizes 
The note of interest to me: “stays suspended” and “no plasticity.” Those two do not fit clay chemistry with one exception: high calcium content. Calcium will keep fine particles suspended when “common plasticizers” are absent. The melted blob at cone 6+ indicates total alumina content is 15% or less. If you want to work with it, I will post some fixes. If not, enjoy the wild clay adventure.
Tom