Harvesting your own clay?

Permies have lots of uses for clay, and per our ethics shouldn't import it to sites if it's available. So how many of us are sitting on clay mines?

Besides gleying, cob, protecting buried wood from moisture, RMHs and pottery, we could find unlimited uses for clay. Traditionally, it was a key part of many appropriate technologies. Plus, removing it from certain areas may make the soil more useful (to us: what do nonhuman animals use clay for?) or amendable there.

I found this labor intensive, low yield process
 with a casual search.

I've noticed that clay tends to collect, or soil to erode, in particular areas of my driveway that was cleared with an excavator a month ago. If one were to exploit topography, wouldn't a series of channels potentially create a passive clay mine? Where either the soil is washed away leaving easily-purified large clay deposits, or the clay is washed into certain collection areas? Per observation, I don't think the latter actually happens...what looks to be happening is that, after human disturbance, sand and soil are removed from settled areas of clay.

Hi Fredy, thank you for sharing this. I live in an area where the soil is pretty much clay based. It would be very nice to be able to transform what is often seen as a problem in a valuable resource. Thanks!

In this area every thing is clay with varying amounts of top soil on top of it. I've seen from 0 to 12 inches. There's a county park lake nearby which much of this area drains into. When that clay runs into the lake it becomes silt. They occasionally dredge the lake and recently they drained it and got rid of the silt. I've heard they had trouble getting rid of it. I don't know why. Seems like it would make a good base for top soil. Anyway, I'm wondering why clay turns into silt.

John, getting rid of silt does seem weird. If I understand its place in the soil profile, I'd think a pile of silt dumptrucked to the top of my driveway would be a blessing!*



____
*Unless, of course the lake is at a topographical low point including e.g. brownfields and factories, &c.

We have a lot of clay in the soil here. I have found pretty pure clay in creek or river beds, although I assume the river beds are more polluted.
John S
PDX OR

silt doesn't turn into clay or vice versa clay is the finest particles and silt is slightly larger, a simple test is to put a bit in your mouth, clay feels smooth whereas silt will feel gritty.
Sediment from lakes and drainage ditches is considered an Enviromental health hazard, it collects any toxins so if you have commercial ag or industry or even traffic in your area all the heavy metals etc will be in that sediment, that is why it is hard to get rid of.
My soil is an old lake bed (drained 1860's) so it is a sand and silt mix with nearly 0 clay, it is great soil to grow in, but it does have many of the issues of clay soil to a slightly lesser extent.

Clay will only settle out in very still waters, so large deep lakes and the deep ocean, which is why trying to trap it will most likely only get you silt.

Skandi

Thanks for the reply. Your right. Now that I think of that, I wouldn't want it in my veggie garden.

But to continue, when that lake empties into Pine Crick and it winds up in the Ohio, the Mississippi, and flows into the ocean; it becomes sand.

Well it doesn't technically become sand, but sand is all that is left that you can see, the clay parts will wash further down the delta and be deposited in deeper water, in a few million years it will probably be a very nice oilfield (Sorry I am an oil geologist by training!)

Our house sits on clay. I don't know how deep, but at least 1 meter.
The cellar needs some height extension, so its a win-win situation.

Extraction process is the following:
- digging chunks (not too thick ~ 2.5cm thick) of clay from the ground and putting it into a container that is then filled with water.
- waiting at least a day
- stirring the soup with a stirrer.
- waiting some more (optional)
- pouring a portion into a steel pasta sieve and stirring it.
- collecting the clay that drips out of the sieve.

It requires 10-15 minutes make a bucket of clay.

Thanks all, I had never considered the difference between silt and clay.

Sebastian, so rather than straining the clay through a cloth bag as is often suggested, you just let the sieve drip clay and water and the sieve retains the larger particles? 10-15 minutes for a bucket of clay seems a worthwhile investment, depending on the composition of the clay. What are you going to do with it?

Skandi, you mean that over time silt does not weather into clay, ultimately? My soil profile is silt loam with some areas of loamy sand, but that's just Soilweb data. I'm finding more clay than the profiles suggest.

The clay is used for everything, really.
- plastering the brick walls (mixed with sand)
- mortar (mixed with sand as well)
- insulating plaster (mixed with perlite)
- building putty (Mixed with linseed oil): Here the clay is used as it comes out if the ground. The processed one contains too much water. The putty It sticks to wood, brick, metal and clay and hardens in two steps: First the water evaporates, causing it to shrink a bit. Then the linseed oil hardens over time.

I guess try to use the local geology if possible.  It might help to do some dry processing first.  I noticed that it's easier to screen dry soil than mud.  Wet processing is effective but can be time consuming.

An other idea for dry processing is to use a cyclone separator.
http://en.wikipedia.org/wiki/Cyclonic_separation


In wet processing to remove water, maybe vacuum filtration would help.
http://en.wikipedia.org/wiki/Vacuum_ceramic_filter

Or use slip casting to help remove water with a plaster mold.
http://en.wikipedia.org/wiki/Slipcasting
 

Fredy Perlman wrote:
Skandi, you mean that over time silt does not weather into clay, ultimately? My soil profile is silt loam with some areas of loamy sand, but that's just Soilweb data. I'm finding more clay than the profiles suggest.

That's going to depend on your climate, Mechanical weathering doesn't have much effect at the scales we are talking so it's down to chemical weathering to change silt to clay. I am not 100% sure but a lot of silt is not going to ever change into clay due to it's chemistry. I wouldn't expect chemical changes to have much effect in a time period that humans can use. We have silty sand here but we do find "nuggets" of clay in it, that's where groundwater has been moving around and deposited all the clay it can move into small areas, giving an impression of a lot more clay in the soil that there is as a overall %. We certainly do not have enough to do anything with, but a few miles up the road my parents in law have enough in their fields that the neighbour comes and collects it for pot making.

Hello everybody

I see that the classic confusion on clay, silt, sand is raising its head once again. Remember for each of these words there are at least 2 or 3 different definitions that overlap.


Clay is 1 word for at least 3 different things. To confuse matters even more the 3 different things overlap somewhat in practice.


Clay 1st definition is a sediment particle that is smaller than 2 micrometer (aka 2 micron or 2µm). This definition is purely based on grainsize or granulometry. Any naturally occuring - non organic - soil particle smaller than 2µm is clay 1st by this definition regardless of chemical or mineralogic compostion.
Because of its small particle size, fluids cannot flow easily trough clay (1st).


Clay 2nd definition is a mineral that consists out of Silicon, Oxygen, Aluminum and potentially a whole bunch of other charged particles. IN GENERAL the claycristals (2nd definition) rarely 'grow' larger than 2 micron. Hence the overlap.

Clay (2nd) is often electrically charged over its external surface. That is the base for a lot of the usefull properties of clay. It holds magnesium-, calcium-, iron-, manganese-, copper-ions etc... to neutralise its charge. It also holds hydroxonium (H³O+) so it helps to buffer soilacidity - in other words it can help keep the soil pH neutral despite acid rain and such. The ions (=charged particles) are adsorbed on the surface. https://en.wikipedia.org/wiki/Adsorption

Clay (2nd) has a platelike cristal-lattice. Basically the stuff consists of layers of Siliconoxide and Aluminumoxide. In between these layers even more ions can be captured - this are absorbed between the layers. The smaller the ions are, the easier they absorbed in the internal structure of the clay. https://en.wikipedia.org/wiki/Absorption_(chemistry)
The absorption is not limited to ions. Clay can also absorp small dipolar molecules like water. Clay minerals that are very good at absorbing water expand their structure. The cristal becomes bigger it swells. Such clayminerals are wel known to permies, builders and petroleumguys alike as bentonite-type clays.
A dipolar molecule is a molecule that has an uneven distribution of its electromagnetic properties. Such molecules behave as small magnets.

Clay (2nd) is generally also has a platelike shape. It's diameter is far larger than its thickness. That is one of the reasons that clay deposits only in very calm water. Playing with the ion content of the water can have an influence on the speed of sedimentation. https://en.wikipedia.org/wiki/Flocculation

Clay (2nd) is formed when other minerals weather chemically. There are hundreds of species of clay minerals. The more unstable a mother mineral is on the surface of the earth the more easy and the faster it changes into clay. Volcanic rock is generally fertile because it consists mostly of minerals that are formed between 750°C and 1500°C. The stability of these minerals under surface conditions is low - they weather fast and rapidly form claysoils. Volcanic rock is mostly rich in magnesium, calcium, manganese, iron, etc... So clays forming out of volcanic rock tend to be very fertile.

There is lots to tell on clays - if you want more - this link is a good starting point. https://pubs.geoscienceworld.org/claymin



Clay 3rd definition is a soil/sediment science definition based on granulometry/grainsize. THIS definiton does not take into account volume of organic material, rock, boulders, etc.....
Clay SOIL (3rd) consist out of a Clay (1st) which may in its turn consist out of Clay (2nd). Mixed in with the Clay (1st) are variable volumes of SILT and SAND.
The exact definition of claysoil is different from country to country - hoera, if possible even more confusion. Clay (3rd) is often defined by way of a 3way diagram. Belgium, the US, the Unesco, etc... all have different definitions of what is clay (3rd) soil.
Whatever the national origin of Clay (3rd) it is generally good to encapsulate and protect organic material and other stuff from oxygen. Hence Skandi's remark about future oil fields. That is also the reason why clay soils are often blueish green to black at depths where sandy soil has a rusty colour. Organic material and Fe²+ are not completely oxidized.

https://en.wikipedia.org/wiki/Soil_texture#/media/File:SoilTextureTriangle.jpg



https://en.wikipedia.org/wiki/Soil_texture



Silt and Sand can also be defined from a granulometric, mineralogic and pedologic point of view. Silt and sand also have different adsorption and absorption properties depending on their mineral content. Hard and hard weathering materials tend to dominate the composition of sand. Such minerals adsorp little and absorp even less. The grainsize is bigger so the pores in between soilparticles are more connected. Liquids can pass easier trough silt and especially sand.


You can capture clay (1st) and clay (2nd) by way of sedimentation but you need to reduce water speed drastically. In a horticultural sense/soil improvement that is almost unheard of in western agriculture. In Egypt, it is being done for thousands of years.
I guess you could do it by building a structure similar to a rice paddy - you bring in sedimentrich (hopefully clayrich) water  AKA muddy water trough a narrow, fast flowing canal and then you bring it in a broad, pondlike, flatbottemed bed where you want your clay to sediment. Plants in the bed can help to capture the fine sediments.
With this process you will not harvest pure clay usable for pottery.
I would not recommend this proces for general use in permies. After all - undisturbed soil in situ is almost always the best.


BEWARE Because of the adsorption properties of clay (1st and 2nd) and the absorption properties clay (2nd) and the tendancy to preserve organic matter in clay (1st and 2nd) ALL KINDS OF POLLUTANTS tend to build up in your sediment. Some of these remain harmfull. Sludge is considered a potential environmental hazard for this reason.

Erwin, amazing!  I learned a lot from that.  

It's interesting that the volcanic minerals used, like perlite and vermiculite are porous, I suppose because the dissolved gases and moisture are what tend to raise the magma/lava flows to the surface.   And then supposed this porosity helps let air back into the soil.  Also has more surface area so it weathers faster.

As you suggest, clay can be like a sponge for certain hazardous substances like naturally occurring heavy metals.  However it could be quite complex to know if and when the sponge was mopping up the metals or wringing them out.  (This issue worries me though when people talk about re-purposing the "red mud" or bauxite tailings of aluminum mining.)  I don't mean to be alarmist, but if you put the wrong kind of clay on your land, and then maybe you irrigate with salty river water, (or the river floods) in the worst case I guess there could be an ion-exchange that could leach out heavy metals.  Yikes!  

There's probably a way to do a soil-test first to see if this is a concern before spreading a lot of clay to be 'weathered', especially if it may be exposed to mineral water.  Still, I would rather play it safer and only use on-site soils.  You're right though, river deltas are supposedly cradles of civilization because the soil is so fertile, although i don't know whether that is a result of: fertilization, irrigation, washing away accumulated residues, or some combination.  Fascinating whatever it is.  

Nice Erwin very detailed explanation, thanks for sharing those insights.

All soil particles start out as rocks, as rocks are ground up (weathering) the particles get smaller and smaller, this is how all "dirt" gets its start.

Solid mountain breaks down to boulders breaks down to large stones breaks down to small stones breaks down to gravels breaks down to sand breaks down to silt breaks down to clay. I did get that right didn't I?
Oh, and it does't matter which type of rock you start with.

Redhawk

A

s you suggest, clay can be like a sponge for certain hazardous substances like naturally occurring heavy metals.  However it could be quite complex to know if and when the sponge was mopping up the metals or wringing them out.  (This issue worries me though when people talk about re-purposing the "red mud" or bauxite tailings of aluminum mining.)  I don't mean to be alarmist, but if you put the wrong kind of clay on your land, and then maybe you irrigate with salty river water, (or the river floods) in the worst case I guess there could be an ion-exchange that could leach out heavy metals.

One of the ways to wring metals from clay is by replacing the metal-ions with smaller ions such as H+. This occurs when you spil acid in your soil medium or if you have a naturally acid soil or if you add organic matter without checking out the soil pH. In tropical conditions you have the same kind of effect with the high troughput of rain/carbondioxide/humic acids trough your soil. Thats how you get Bauxite in the first place. Tropical soils can become so weathered and leached that you automaticaly increase the concentration of the most stable elements in that soil - basically that's bauxite.

You are correct to be very sceptical about bauxite tailings (and most other tailings) or indeed almost any industrial waste product. Remember this ? https://en.wikipedia.org/wiki/Ajka_alumina_plant_accident
It is not alarmist. This is a real issue. Here are some anecdotes.

Speaking of putting the wrong clay on your land, it happens al the time naturally and not so naturally too.
Each time a polluted river floods - polluted sediments are deposited in the flood plain. THAT's real science by the way (in a reaction to the discusion on good and bad science elsewhere on permies). We have plenty of such land here. Heavy metals in concentrations around 5000 ppm ~ 20 to 25 times normal not counting other pollutants.
Years ago, a german colleague told me about a certain port on a certain canal near a battery plant. The farmers of the region where fond of the sludge dredged from the bottom of the canal because of its fosforous content. However after a while it turned out that the battery factory had used a permit to get of polluted waste water into the canal. The sludge (mostly sand, clay and organic matter) spunged up the heavy metals and that got deposited on farm land as well. Those farmers found a lot of trouble that way.

The moral of the story is that if you have no reputable (preferably totally independant) source to confirm that no pollutants are present and that no ill effects accrue over the long term, you better damn well know what you are doing.
If you have some plant offering waste products as soil improvement check out the BATNEEC-studies concerning that industry and check with your administration/local environmentalists about potential issues. https://en.wikipedia.org/wiki/Best_available_technology

If you really want to increase clay content of your top soil you can in most cases do it by taking the clay in the B-horizon of your soil http://nesoil.com/properties/horizons/sld007.htm that requires digging which is anathema to most permies. However, i think it is permissable in exceptional circumstances. (Mitigating possible soil pollution or increasing local groundwaterinfiltration being two.) It is certainly better that bringing in dubious clay from elsewhere.
This may modify your groundwater movement in your soil - so check groundwaterlevels before you do this. If your groundwater sinks 10 m deeper, you have a major problem.
DO NOT DO THIS IF YOU HAVE ANY SERIOUS KIND OF GROUNDWATER POLLUTION, removing clay may make it much worse.
That said in Europe this proces (uitbrikken in Dutch) was done to produce bricks locally and to improve drainage.

A potentially safer source for clay is the product of plants where sugar beet and patatoes are washed. You may have pesticide residu but with good judgement you could use it. I still recommend chemical analysis. Farmers bringing their harvest to plant, usually leave with a freight of washed soil it they don't wash on the farm. It is routinely controlled here. I'm not aware of major problems in Flanders.

I totally agree with you Erwin, Here in Arkansas, USA we went through a 20 year period of people using Aluminum waste material as underlayment for foundations and road beds. No one thought about the consequences of using this "Donafill" material.
It didn't take long for surrounding soils to become so acidic that nothing would grow within 30 feet of the donafill, finally independent lab testing was done on the donafill and it was rife with not only acids but heavy metals. It is no longer allowed by law.

I've done testing of our red clay layer since we have areas that it is at the surface, it was nice to find that it is not contaminated and suitable for pottery use with some sand added to it.

Redhawk

I'm just getting back to this thread..

Erwin, that was amazing. I have read it twice and am still working on understanding it fully.

Sebastian, I am really looking forward to trying your refinement process and the applications for the clay!! We get a lot of rainfall here and if I hope to figure out how to wash out non clay elements with some kind of trap and sieve.

Bryant, how did you test your clay? And how do you harvest it? I'm not thinking of it for food applications, but building, gleying and insulating mostly. I need to find out the parent material to see if it's even a useful type. Or try some harvesting techniques and play!

Epic post Erwin!

One would need a way of testing soil.  I'm a novice at this but I suppose one could put the soil sample through an appropriate sequence of an acid wash and/or an alkaline wash of a pH range that the soil is likely to encounter, and see what comes out.  I guess the question, on a case-by-case basis, is what to do with the heavy metals given that they are in the earth.  Do you leave them where they are, or move them, or plate them out?  

I was chatting with a guy on facebook "BigAtticHouse" who works with electrochemistry and "geopolymer" batteries.  Maybe that's one way of dealing with such soils.  If you have a contaminated soil, in theory one might be able to mitigate it with some kind of electrochemical cell.  Put an electrode into it and make the surrounding soil into an electrode.  Then put another electrode somewhere and use an electric current to try to drive the heavy metals into a more stable soil, or try to plate them out.  

But I don't know how well that would work.  It seems very easy to make matters worse.  And it seems like a huge gamble as to who is legally liable for such things.  If you just leave it in the ground, I guess it's nature's fault and no one is liable.  But as soon as anyone does anything, especially if they dig it out of the ground then it's a liability and I guess whomever possesses it is responsible for it.  All of that is worrying and it seems like the more people mess with it the more of a tangled mess it becomes, even though they may mean well.  

I don't know, I could be wrong but I suppose that's why I'm of the opinion that mining residues ought to immediately be put back where they came from, and left there until the technology, knowledge and resources become available for them to be considered mineable ore again with an independent business plan that appropriately accounts for all the liabilities.  I think it's problematic that the seemingly emerging business of bauxite residue processing that tries to chase down every last trace element when humans have the well-intentioned but naive dream of imagining they can make the entire earth pristine clean.  It just doesn't seem possible.  Maybe those residues are just spent ore that ought to be left alone.  They might just be causing liabilities to exceed profits and/or spewing waste everywhere as this stuff gets redistributed.  

It's worrisome.  It's not always clear how knowledge and technology should be used.  Sometimes more is better, sometimes more is worse.  For example even with all the knowledge and advancements in agriculture, all of it had to be scrapped in a return to a natural model of permaculture.  

I guess just use the soil that is on site.  If nature's acid rain makes the soil naturally leach toxins, well... it was probably going to do that anyway through natural processes in nature.  

Hey Mike,

In response to you. Some loose thoughts/comments - we're drifting a bit off topic here.

One would need a way of testing soil.  I'm a novice at this but I suppose one could put the soil sample through an appropriate sequence of an acid wash and/or an alkaline wash of a pH range that the soil is likely to encounter, and see what comes out.  I guess the question, on a case-by-case basis, is what to do with the heavy metals given that they are in the earth.  Do you leave them where they are, or move them, or plate them out?

That is basically what is being done in some cases. It's called leach testing. There a bunch of methods. Which one to use depends on your legislation and how to assess the results depends on legislation as well.
For permies 99,9999 % don't need it. Luckilly -as these leaching tests - are often very expensive. In my region (Flanders region in Belgium) prices range from 89 to 389 € depending on what test is required. There may be prepping costs and waste disposal costs as well. It is expensive and if you don't know how to sample correctly or know how to assess the results it is an utter waste of money.



It is very easy to make things worse in soil remediation. That's why - in Flanders at least - companies offering soil remediation have to be
   Licensed
   Insured
   Independant from the owner/user/polluter of the land
   Qualified
Their work is checked by an independant consultant who reports to the local government office. So a very rigid system but new owners have a reasonable level of protection.
It is - certainly in the US - very easy to become liable and even if not - it looks really easy to become the target of litigation. What for instance is your obligation vis a vis a new owner/user of the land you sell because of the pollution you have had measured? I certainly would feel bad about selling a property to a family that's going to grow food there.

Luckilly permiestype soil management is generally very good to decrease the risk of soil pollution. Mind. I did not say decrease the soil pollution !!!



Soil remediation should only be done in places where man has altered the soil composition badly.

In nature there are places where the soil naturally contains heavy metals, oil, etc..... In general in such places you have a natural flora and fauna adapted to such an environment. I suppose everybody can understand that you will find heavy metals in soil on top of a metal ore vain.
But there is also some increased heavy metalcontent in soils formed on some kinds of bedrock. One example is copper (Cu) that may be enriched in soils forming on basalt. Some of that enrichment makes for good plantgrowth but it may accumulate in plants to a level that is of concern. See further


(Sorry don't know links to english examples). Plants adapted to high levels of zinc (Zn).

https://nl.wikipedia.org/wiki/Zinkviooltje
https://nl.wikipedia.org/wiki/Zinkflora

I agree that the mining industry has an abysmal record concerning mining waste. Recuperating mining waste has been done for thousands of years. After all - you don't have to bring the stuff to the surface. I think working the ore to extract all usable stuff and stabilise the rest, is probably the best method to handle mining waste. That leaves acid mine drainage - a major environmental problem.
https://en.wikipedia.org/wiki/Acid_mine_drainage
The mining industry has been or is doing badly but not alone sadly. It is however one, US-permies are possibly a little more likely to encounter than EU-permies as the focus in the US seems to be on going off grid (~off 'rules' for the mining industry?). You rarely find metal mines in a city.

Only one advise don't set up shop in such an area.
If you have and are stuck in a polluted area - you really should read a lot, before being able to grow food safely. We have had an international project called BeNeKempen designed to give farming advise for farmers and home growers in a polluted region near the dutch border east and north of Antwerp Belgium. Sadly i have not found an english translation yet.


Coming back to that level of concern, i mentioned above. Any food you grow in soil will take up components of that soil. A tomato grown in hydroponic culture will grow fine (but it will be tasteless).
A tomato grown in some soils (Cu-rich basalt derived soils f.e.) may contain more coper than usual. If you cook lots of such tomatos and reduce the watercontent by cooking, you simultaneously increase the concentration of everything else (including coper) in the remaining tomato paste. If you make ketchup out of such tomatos you add vinegar whick mobilises the coper. Al that while the initial increase in coper in the tomato is way below the norm for fresh tomato. So, tasty tomatos are best enjoyed fresh
The best tactic to remain healthy in a polluted region is to source your food from many different places, eat it fresh, avoid to processed food and go easy on the ketchup

I use a pick and shovel to dig up the clay, then it goes into a 55 gal. plastic barrel and I add water and stir like the dickens for about 10 minutes. Once that settles the pure clay will be the top layer and I use a shovel to scoop that out once I've drained the water out with a syphon hose.
You have to watch because clay will have some stones in it straight from the ground, when you get to those, it is time to stop harvesting clay for pottery.
Next step is to let it dry out for a few days so it acts like moist clay in your hands, this is when it's time to add the sand and mix it to homogenous and bag it, you don't want to let this mix dry out.

Mike Phillipps wrote: I could be wrong but I suppose that's why I'm of the opinion that mining residues ought to immediately be put back where they came from, and left there until the technology, knowledge and resources become available for them to be considered mineable ore again with an independent business plan that appropriately accounts for all the liabilities.

Remember the 2015 Gold King Mine wastewater spill in Colorado? Mining will always entail injury to workers and environmental damage, now or later. To say nothing of radioactive ores! Isn't it baked in the (yellow) cake? (Sorry, couldn't resist.) If I were more learned in the area perhaps I would stridently argue for 95% recycling of all metals but pretty sure, as a self-taught welder, that metallurgically that is not tenable.

This thread has accidentally made me very glad there is no mining history in my area.

Thanks for explaining your method, RedHawk. I look forward to some clay harvesting---let's not say mining---soon!

My subsoil would be classified as silt. I use if for cob projects as if it were clay.

Edited to add: This cob cookstove was made using my topsoil...! Hee hee. Loving the fertility of my garden.

Joseph Lofthouse wrote:
My subsoil would be classified as silt. I use if for cob projects as if it were clay.

At the risk of sounding repetetive, how do you harvest and process it Joseph? There are many good ways, there might be one best way, or it might always vary by soil composition.

Perhaps you'll laugh at me when I tell you how I harvested clay most recently.

During the growing season, I do minimal weeding. So my field is filled with waist high dry weeds and crops, etc... I ran the tractor/tiller over it to incorporate all that cover crop back into the soil. Woot! Looked just exactly like cob with straw already added. So I scooped it up, added water, stomped it, and used it to make the clay cookstove show previously in this thread. The field has very few rocks, so it worked great.

I have also use kola RedHawk's method of adding subsoil to a container, adding water, and stirring like crazy. Then I decant leaving behind a few rocks, and a hint of sand. I might pour it through a 1/4" to 1/2" mesh to remove roots.

Joseph

If it works, it works.

As i explained above - you can have 'silt' by soil classification but that can still have a lot of clay in it.

My soil would classify as sandy loam (~ silt). The toplayer of such a soil gradually loses its clay component due to the washing down effect. That is water seeping trough and washing out the clay particles. These are deposited lower down in your soil profile at the level where your groundwater fluctuates. So that level sees a build up of clay (and often iron and manganese oxide/hydroxide minerals in a temperate climate).

That's the level i use to harvest clay, gley ponds and that's the level i break/hand-drill open to infiltrate more rain.

Just a few houses down the road they used to harvest the clay build up in the soil to produce bricks. That very local harvesting disapeared only after the industry learned how to work the tertiairy sea clay deposits using coal fired ovens.
The way it worked was that anybody wanting some construction done asked a brickmaker to come round. The brickmaker looked for suitable clay/silt deposits near the site. Fuel (first wood later coal) was carted in and the brickers made the oven, bricks and sometimes rooftiles from the local clay.

Before that, they thatched houses here with the sandy loam and or clay mixing it with straw and horse manure. So old houses are often build with materials almost literally from their own backyard.


My house is ± 85 years old - some of the plastering and internal roofing is done with local sandy loam. The brick is probably first and second generation industrial brick form marine clay.
It's a bitch to restore walls with loam finish because the knowhow to do it with local soil is lost. Shipping it in, costs an arm and a leg.

So Freddy/Joseph the technique was good enough to allow semi-industrial (but lowly mechanised) production.

Greets
Erwin

CRUMB!!!

I thought to weigh in on the discussion. Seeing as I am in search of a method for the synthesis of geopolymer mortar from the abundant feldspar-gneiss-syenite on the mountain that I may have acquired.... clay is related (a waypoint in the process I am investigating is kaolinite - a product of feldspar - prior to polymerization....).......

All this stuff about heavy metals!! CRUMB!! CRUMB I SAY!!! C.R.U.M.B!!!

Yes, things like chromium and lead are a problem when they are in places, but, guys, they're as natural as Dihydrogenmonoxide!! (You see what I did there?)

It occurs to me that the purpose of this forum is not to repeat demonization-propaganda of a given element or compound (the dioxycarbon for instance?) but rather to recognize how AWESOME these things are when some smart human looks and says "Hey! you don't belong here, let me help you find a better home!"

I understand that there is an issue with mercury in dirt, but there are plants that like that sort of thing. Lead? There is this curious thing that happens when gypsum is messed with - then the sulfate finds the lead, and PRESTO! Galena!!! Galena is pretty, and not really a problem.

There are all sorts of cool Alchemical ( ha! ) methods to benify, nullify, friendlyize, and even use whatever it is that might be in whatever it is that you might have!!

Yes, it is work. Ummmm.... permaculture is not for suburbanite yuppies with 401K's who-die-in-assisted-living-facilities-after-paying-for-someone-else-to-provide-everything-during-their-useful-years now is it??

I'm not saying that everyone become a chemist, or an alchemist (which is cooler), but we all ought to at least be apothecaries right?? :)

In summary: Yes, "heavy metals" (iron ain't light - I assure you!) are mischievous little wankers, but they're just like the rest of the Table - they just want to find a friend and go home!!

CLOSING TIME!!!

Don't bad-mouth the poor, lonely elements... find them a friend and give them a home! (Perhaps as a constituent of the glaze that you put on that clay you're harvesting???)

I feel like I'm too stupid to talk to all of you, but here goes.   I understand the environmental impacts of removing large amounts of clay and placing it elsewhere, and also the bit about pollutants leaching into rivers and creeks, thus contaminating clay soil beds.  My question is, how dangerous is it for ones health to harvest clay for pottery from general areas, say from a creek in a small town that has only 100 years of industrial and mining operations that ran at least 100 miles north of said creek bed.(I'm not too sure where the creek ultimately flows from).  Is there a way to tell contaminants by color or smell?  Also is a small amount of silt harvested with the clay okay?  Also can harvested clay from pottery harbour microbes and parasites, ( that sort if thing).
Thanks.

This is 25 years ago now, but I read that in our modern context, it's pretty easy to find nearby road construction projects and they often expose clay deposits that are less polluted than stream-banks which concentrate pollutants for an entire drainage basin.

Also, my bet is that most stream-bank clay is pretty safe, but it's not a sure thing and you'd have to either have it tested or decide how risk-averse you are.

I have a nice clay deposit at the key point of a valley on my property. My understanding of Sepp Holzer and PA Yeomans is this is pretty common, and why key point dams often work with native material. The key point, where the slope goes from convex to concave, often has naturally deposited clay particles that were carried there by water flowing over steeper slopes and then dropped out of suspension when it stopped. Water moving faster or in larger volumes carries particles of exponentially larger size. River deltas, mouths  and confluences are great places to observe the result of this pattern in rocks of descending size being deposited as the water slows. This makes key points natural places for deposition and helps greatly in building dams/pond keys (clay core)  on such sites, which can be made with as little as 1/3clay, and according to Holzer and others this can usually be found at the right place in most valleys.

Fredy Perlman wrote: If one were to exploit topography, wouldn't a series of channels potentially create a passive clay mine? Where either the soil is washed away leaving easily-purified large clay deposits, or the clay is washed into certain collection areas? Per observation, I don't think the latter actually happens...what looks to be happening is that, after human disturbance, sand and soil are removed from settled areas of clay.

I remember that Holzer wrote in his permaculture book about how they did exactly that to accumulate resources over several years to be able to build their house.