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Posts: 59
Location: Bellevue, WA
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Hey folks,

So I've got a new obsession...terra cotta.  It's a material thats ubiquitous in gardening, but has been relegated to just being what we put our plants in. Please bear with me if this is all old-hat to you, but for me these discoveries were kind of mind-blowing. 

What got me interested in terra cotta was my honeymoon in Mexico. During one of my tours around the area I came across a large, hear-shaped terra cotta jug resting on a stand above a second, glazed terra cotta pot.  When I asked our tour guide about it he said it was a water filter. His english was broken, but what I got from it was that before the area was widely settled the locals would go down to the ocean and hike back with a jug full of salt water. That water was deposited in the heart-shaped terra cotta jug and, overnight, it would filter through the clay and and collect in the glazed basin below. He claimed it was still salty tasting, but palatable and it was how the locals survived in such a hyper arid area of coastline.

This kind of blew my mind. I've read about ceramic filters before, but I've always carried a mental image of very specialized clays or the like and certainly not rough-hewn terra cotta.

That got me looking deeper. I then found the practice of using Ollas in gardening. Ollas are long necked, pumpkin shaped jugs that are buried in the garden up to about an inch below their openings. The garden is irrigated by keeping the ollas topped off. The water is leeched from the ollas by the surrounding soil, which is then in turn taken up by the nearby plant life. As the plants require more water, the soil pulls more water from the jugs.  It's a very water-efficient system for arid locations, as what the plant/soil needs is what is taken, no more or less (as long as the olla is kept topped off and loosely capped).

So here I had two great examples of terra cotta's water transference ability being harnessed for filtration and irrigation!

I also stumbled across this article where a gentleman has found how to increase the water transference rates of terra cotta without reducing it's filtration properties too greatly.

This now has lead me to start looking more into the surface area of terra cotta.  It's porous nature would seem to hint at a structure much like charcoal, which as permies have been pointing out, has an amazing surface area for moisture, nutrient, and biological activity retention.  I'm looking into that property now, because it would would seem to me that using home-cast, disposable ollas in arid perennial gardens and allowing them to wear out and simply allowing the broken shards to become amended into the soil would both provide an amazing way to irrigate as well as providing increases soil quality over time.

Has anyone else looked into terra cotta or have any anecdotal experiences with working along these lines?  I would love to hear other folks thoughts, opinions, ideas, etc

Cheers!
 
Emerson White
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No ceramic filter can remove salt, you need reverse osmosis or distillation for that, perhaps they were gathering water from an estuary. Humans can actually survive on less water if they cut their fresh water with 25% sea water (a final specific gravity around 1.006) but you still need fresh water.
 
Joel Hollingsworth
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I could imagine using seawater for a number of uses (soup, pickling, flavored wine), but I definitely would want to filter it first.

This could be an important trick to know, because I live next to a large body of brackish water, with a high population density and low annual precipitation.
 
Brenda Groth
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intresting..here in the cold wet north terra cotta isn't a great product as it can't handle our freezing and thawing..and distillation is much safer for desalinzing water..however..i can see in the arid south where this would be much more interesting..

i enjoy reading things even if they won't work here though
 
                                            
Posts: 59
Location: Bellevue, WA
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I live in seattle, so I'm looking at tempurate applications.

If you're thinking of using ollas, they should work even in areas that freeze. Being buried, they'll remain at a slightly higher temp than ambient air temps. Even better if you mulch heavily around their necks during the cold season.

I'll look more into the salt water/terra cotta filtration, since my guide was very insistent that they used the sea water in the village.  I'm now wondering if it's less a filtration action and more of a condensation trap system (terra cotta stays colder than ambient air temp due to evaporative qualities of the material when filled with water). If you had a large, properly shaped vessel filled with salt water, it would collect and drip fresh condensation from the surrounding air, provided there was enough airborne moisture.

I'll keep poking around

 
                                
Posts: 55
Location: Savannah, GA
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There is a picture of something very similar on page 13 of the book Water Storage by Art Ludwig. The caption reads, "Old-fashioned drinking water filter/cooler in a farmhouse in rural Cuba. The owners pour raw water into the depression in the porous carved stone filter. From there, it drips into the clay storage urn. Louvered vents (in the cabinet) provide evaporative cooling."

It is not specified what is being filtered out. If I remember correctly, salt that is dissolved in water bonds molecularly with the water and cannot be filtered out by normal means but only by distillation or pressure osmosis.

As a former potter I know that when clay is fired into terra cotta, it undergoes both a chemical and physical change and cannot be returned to its former state of being clay. So I'm not sure how much soil improvement would be gained by terra cotta fragments in the soil. It would not be the same as adding the same amount of clay to the soil.

Terra cotta does have an extremely porous nature, but the small pores are easily clogged by minerals in water. Disposable ollas should work to filter water of some minerals and slowly disperse water into the soil, but I'm dubious about their utility after they clog up. Hope you can prove me wrong!
 
                                            
Posts: 59
Location: Bellevue, WA
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Actually, amending the terra cotta into the soil isn't about trying to return it to being clay, but actually taking advantage of the poruous nature of the terra cotta for microbiotic life, nutrient retention, and moisture retention.  It's downside of clogging when being used to irrigate or filter water is now being used as being beneficial, as it can help hold the above mentioned elements in your soil much the same way charcoal would.

I would love to get more of your insight, as i've never worked with clay before in any way.  I've been reading about adding fine grain organic matter to the clay before firing to increase it's porosity. Would this make the clay more brittle or cause it to be more likely to crack during the firing process?

the article I was reading about was talking about adding coffee grounds to the clay and the firing process would burn it out, leaving behind a trace of silica along with increased porosity. 
 
Emerson White
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Bert, keep in mind that the amount of water that condenses on the cold surface will be equivalent to the amount of water that evaporated, because the heat of condensation is the same as the heat loss of evaporation. Some warmth is also picked up from the environment and radiated into the night sky so it will not be exact, but if that effect is how you get fresh water than it is a form of distillation. No matter what the thermodynamics of making fresh water from salt water are not friendly.
 
                                
Posts: 55
Location: Savannah, GA
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It's been a long time since I did that kind of thing, and I don't have any books on that subject any more, but I'll see what I can dredge up from the memory banks...

Yes you can add organic matter to the clay and burn it out in the firing process. I think the firing atmosphere must be an oxidizing atmosphere at least until the organic matter is burned out. The clay must be heated just to the point where the organic matter burns away and held at that temperature until the organic matter is gone. Then the clay is heated to its firing temperature as normal. The thing I would worry about with the coffee grounds would be explosive combustion of coffee particles that were completely embedded in clay - could result in a crater. I remember being warned about that sort of thing but never had it happen to me and never did any experiments with organic burnout, so this is what I remember from reading. The coffee grounds should probably be dry when added to the clay and everything should be dried completely before firing. Water will come out as steam at a lower temperature than the coffee would burn and could also cause holes in the clay vessel. As long as there is more clay than coffee grounds, it shouldn't weaken it very much. I'm sure there is a point of no return where there is too much void and not enough pottery, but I don't know where that would be. There is actually quite a bit of technology involved with firing pottery, even in a primitive kiln and even at relatively low temperatures such as are used for terra cotta. I would encourage you to read up on the subject or take a class if you are really interested. The whole process of clay to fired object is fascinating and magical but not as simple as it seems at first glance.

One interesting thing about working with clay is that it becomes easier to work with if allowed to acquire bacteria. Freshly dug clay that is too sterile is not as plastic as clay that has been worked a bit and allowed to sit at room temperature for a few days.
 
                                            
Posts: 59
Location: Bellevue, WA
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weird, so "cultured" clay is more workable than sterile clay....I think you just opened a whole new avenue of research for me to look into as well!
 
Emerson White
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The clay we dug up here went from being a very workable texture to being crumbly and unworkable in a matter of days  I think it depends on type really.
 
Joel Hollingsworth
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As to mechanical damage: voids are a double-edged sword. They can concentrate stress and initiate cracking, but they are also very good at re-directing cracks and absorbing compressive strain. In usual circumstances, they diminish strength (stress without any permanent damage) but slightly improve toughness (energy absorbed before catastrophic failure). Voids are a major reason that terra cotta takes damage so very differently than glass does.

Edit: Mechanical effects of porosity are very familiar to most of us in the case of polystyrene. Compare clear plastic picnicware to a foam coffee cup...it usually isn't feasible to take things to such an extreme in the case of ceramics, though.
 
                                        
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adding organic matter to the clay before firing would not necessarily cause the clay to crack during firing, maybe during the initial shrink when the clay goes from a wet state to "bone dry" which is the state of the clay before it's fired.  Even then I highly doubt if the clay would crack, unless the organic chunks were very large and dense like wood chips or something.  Many potters add straw to clay so that it will burn off and reduce the oxygen in the kiln during firing.  Any clay can be fired to a porous temperature.  Bisque firing is always porous so that the clay can accept the glaze before the final glaze fire.  Terra cotta is a low fired earthenware clay, but stoneware and other clays can also be low fired and they would be porous enough to let water pass through.  As far as the porosity of different clays at different temperatures I'm not sure, but ceramicists should be able to research that and find out. 
 
                                        
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The trick with organic material is to heat the kiln very very slowly, which is easy with an electric kiln, but difficult if you are firing with wood, or whatever.
 
                                        
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btw . . .I just realized that I have some terra cotta in the studio.  I'll do some test fires with varying degrees of coffee grounds ( I have plenty of those too :roll  I'll post pics.  It should be fun.  I only fire my kiln about once every few months though, so it might take some time before I can build enough stuff to fill the thing again. 
 
                                            
Posts: 59
Location: Bellevue, WA
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If you happen to be around the Seattle area, I'd certainly volunteer to help out with the test firing
 
                                        
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I am in Northern California near Sacramento.  I'll probably do some real small scale testing tiles first so as not to "contaminate" too much clay.  I'll make tiles of the same size/dimension and each tile will have a different measure of coffee in it.  I'll see how well they dry ..  .how they stand up to firing, what kind of strength and porosity that they have.  If anything looks promising, then I'll try to build some structures to hold water.  If you have ever worked with clay before then you can understand how it can be a messy process.  I'd imagine that once the wheel and water got exposed to coffee grinds  then it'd be difficult to clean up the mess.  I'll test on a small scale first. . . .because my studio is always immaculately clean-lol.  Sounds fun though.  Firing will be with an electric kiln.  Someday I plan on building a wood fired kiln . . .and then it's going to be a choice for the wood around here between heating the house, building Hugel beds and feeding the kiln.  I already know that feeding the kiln will win out every time.   Put on a jacket if you are cold kids!!!  Hugel beds are cool but . . .firing the kiln is way cooler than that. 
 
                                            
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Hey Tardy,

do you think that terra cotta, submerged in high-moisture soil, would wick/leach water out of the soil?

is there a way to create terra cotta balls?  I vaguely remember from highschool art class that you can't make hollow spheres with terra cotta due to the firing process making them 'splode. But do you think it would be possible to make hollow spheres with a vent hole then slip-cap it after the firing process?

Ollas are cool technology, but are way more suited for arid/hyper arid landscapes. Here in seattle where we have a wet/dry cycle, I'm thinking more about the  potential use of terra cotta for locking moisture into the ground for longer periods (we have a rather big combined storm overflow problem in seattle with rain water rushing into the sound instead of staying in the landscape.)

The theory i'm toying with is amending the soil with terra cotta balls to help normalize the moisture content for areas with pronounced wet/dry cycles.

I'm very keen to hear about the results of your organic-amended clay tests too! There just seems to be a lot of potential in this
 
Joel Hollingsworth
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Bert Harvey "Tentamus" wrote:is there a way to create terra cotta balls?


There are industrially-made clay balls that are fired slightly wet, in such a way as to fluff up while they sinter, but don't quite explode. The finished product has perhaps more void space, and a little smaller voids, than the organic matter + clay mix we've been discussing. They sell them for hydroponics and quite a few other purposes. I think they'd work for what you describe, but AFAIK they're expensive, largely due to embodied energy.

I think a rain-filled or groundwater-filled olla would work for what you describe. It might work better with a traditional design than with a closed top. Buried wood might be a lower-energy (if, arguably, less-permanent) way to accomplish much the same thing, whether that means traditional hugelkultur or something quite different.
 
                                            
Posts: 59
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Hmm, i'll test open topped ollas in saturated soils and see if they'll take on excess water. 

I was thinking of the terra-balls more for being amendments in plantings. like, if you're putting in a new bush/shrub/tree throwing a couple of these in with the back-fill to help balance moisture loads on the surrounding soil and potentially storing water later into the dry season.

I looked at the expanded clay from hydroponics, but they're not quite the same thing i'm thinking. I sorta stumbled on a good, cheap alternative way to test this theory with tiny terra cotta pots caulked together and their drainholes capped. i'm gonna grab a couple of these and see what they do in: full water submersion, submersion in saturated soil, submersion in moist soil. 

I agree that buried wood would likely be an easier method, but for urbanites like me with very little access to woody debris and not a lot of space to bury what I do get my hands on, terra cotta might be a bit more space efficient while providing the same soil-moisture benefits.
 
Joel Hollingsworth
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*nods*

If you do want wood for your soil, in an urban setting, you might check Craigslist under "free": often times in my region, arborists will offer firewood, woodchips, or (more rarely, due to less demand) whole trunks/branches.
 
                          
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Location: Bozeman, MT
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I have two books, which mention primitive pottery (How to make Primitive Pottery, Ancestral Skills II), both of which state to temper the clay (20%) with cattail fluff, which is high in silica. This helps the strength of the pottery. The fluff can also be used in green building, in the finish plaster recipe.

As to filtering water, a friend who was my midwife, had been a missionary in Guatemala many years ago. She said that they used a large pumice jar/basin to filter water. They filled it up each evening and by morning, the water had trickled through the pores and was captured in a large pot placed beneath. I dont know if they boiled the water first to kill any bacterias.
 
                                            
Posts: 59
Location: Bellevue, WA
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Thank you Kathryn, those books sound perfect for what i'm hunting down
 
                          
Posts: 62
Location: Bozeman, MT
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Bert, here are the links on  Amazon.com

http://www.amazon.com/Primitive-Technology-II-Ancestral-Society/dp/1586850989/ref=sr_1_1?ie=UTF8&s=books&qid=1281374262&sr=8-1

http://www.amazon.com/Make-Primitive-Pottery-Evard-Gibby/dp/0943604389/ref=sr_1_1?s=books&ie=UTF8&qid=1281374353&sr=1-1

There is another that I am trying to locate from one of my archaeology reference books. I may have to get back to you on that one. I dont own it yet, but have it noted in some of my research dealing with Old Europe (6000-2000 BCE) pottery. The book is all about the methods of ancient pottery from Old Europe, Aegean Sea territory, Ancient Anatolia, Levant and Mesopotamia. If you are interested, when I locate it, I can let you know.
 
                                            
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please do! i'm a data junky and a bibliophile, so the more books I can reference in my research the happier I am.

If you don't mind my asking, what lead you to researching that topic?
 
                          
Posts: 62
Location: Bozeman, MT
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LOL, I am also a bibliophile and have not run across many people who categorize themselves as such, so nice to see a kindred spirit, as such. Whenever I have moved, my kids have complained about the weight and multitude of all my reference books.

I dont mind any questions. I have been working on a book that involves the archaeology, comparative mythology, linguistics, symbols in artwork of the territories I mentioned and in dealing with the Proto-Indo-European incursions into other territories who were highly skilled artisans, I was having to deal with the symbols on their artwork, part of which involved their ceramics, which are stunning by the way. A great book showing them is The Lost World of Old Europe, The Danube Valley, 5000-3500 BC, by David Anthony.  At any rate, I love ancient and primitive skills, and have learned to do many of them as an artist, but I also find a peace and contentment in working with my hands to create something functional, yet artistic. So I collect reference books on all these skills, for different mediums, from cultures all over the world and differing time periods to learn and surround myself with beauty. Always the student.
 
Emerson White
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If you haven't found other bibliophiles it's because you haven't been looking, there are a ton of us.
 
                                            
Posts: 59
Location: Bellevue, WA
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I think that it was more that most folks don't label themselves as such, so meeting another person who openly admits to it is a nice surprise
 
Emerson White
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Go to a used book store.
 
                                            
Posts: 59
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on here, among other permies.
 
                          
Posts: 62
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Yes Bert, it was more the labeling, but these days, I really dont find that many people who share the same compulsion I have, to own my reference books. Many are internet /e-reader oriented. I have gotten into debates with others on reddit about these e-readers. When I research, I will have at least half a dozen books open at once, flipping through charts, maps, ancient language dictionaries, etc. and I cant and wont even try that with an e-reader and most of my books are probably not available to an e-reader anyway. My living room is more like a library. I was pleased in reading through a number of the posts at this site, to see people referencing many of the books that I own, which lets me know this appears to be a better read group of people than I have come across in quite awhile.

Emerson, I do frequent used books stores, library sales, but sadly, most of what I need, I have to get at Amazon.com used or at Eisenbrauns, due to the nature of my books. I just dont find the meaty  or specialized books, locally here in Bozeman, that often. Not like I have the time to hang out at the bookstore to meet other "bibliophiles", though that might be a nice change of pace.
 
                                            
Posts: 59
Location: Bellevue, WA
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yeah, i can't get behind this e-reader movement. I don't like the idea of not owning my books. When I read about kindle quietly pulling titles from user's libraries that kindle had lost the license rights to offer on their service, I knew it wasn't for me (ironically, the titles they pulled were the works of George Orwell - including 1984)


On Topic, I've installed a couple home-made ollas in my garden (garden pots caulked together) and have a control garden without ollas going as well.  I'm hoping to get my hands on some hollow terra cotta balls for some saturated soil tests this weekend.
 
Emerson White
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I keep a back up of all my books on DVD-RW. I really like my Kindle and it has really lightened my load. I still have cases full of books and buy more often but the e-reader really makes bringing together books and my  life a lot more convenient.
 
rose macaskie
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  I have been trying to keep the ground wet, the terracota way, using flower pots. I thought somone had written of it elsewhere on these forums and it must have been you tentamus except the person talking of it before seemed to have already got his pots installed.
  I have tried it this year. I put cement in the bottom of the flower pots so they would hold water. Cement does not get affected and go soft in water as plaster does but it is permeable as terracotta is too.
    I made a circular lid for the pots in some fairly stiff plastic sheeting i have i use to protect delicate plants from the frost. I made two holes in the circles of plastic i had cut as lids with a heated to nearly red hot gimlet, to thread some string through the plastic that could serve as a handle for the lids. I wanted a tight fitting lid to stop mosquitos developing in the water, though i think the water in the pots dries up pretty quick, in about a week, less, so maybe their would not be time for mosquito larvae to grow up in the water. I have also covered the pots with a slate to stop people putting thier feet in them when they walk round the garden and twisting so their legs. I have got photos of them but i am having problems ldownloading them from the camara.
    The  flower pots are cheaper than potbellied pots with a thin necks but probably not as useful. Flower pots will be more open to the sun and so to being heated by the sun and so thier water evaporates.
  The last time i went up, which was after a week without visiting the garden, the pots seemed to have worked well. I had made a mistake with the drip system however and that was not working. It has now been two weeks since i have been there but when i was there I managed to get a drip on most of the trees that are new so it does not matter if the pots dry out. It seems however that i should use bigger pots if i wish to depend on them as i they might have to serve a source of water for more than a week.
      I used the flower pots that are about a hand high and a hand wide at the top end. I used them in my tiny hugglekulture beds as well as next to the trees i had planted, so i will, if the wood in the beds gets to holding lots of water, have water filled wood and pots that can be hand filled with water.
  They used to have clay waste water pipes instead of plastic ones, with those you could run water all over the place but i dont think they make them any more. If you are using them for your black water the plants could get manure off them too.

  As to using stone to purify water look up stones of the zeolite, there is a wikipedia article on zeolite and that is not th eonly online artcle on it . the rocks that come under this name which are of varriouse sorts are used to  purify water.
  If you are purifying water there is a question of getting germs out of the water and the other question is to get poisons out of the water, like may be cobalt, mercury and such. agri rose macaskie. 
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