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geremyh

Super Amateur Needs Help With Porosity

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geremyh    0

Hello,

I'm making some unique gifts and would like to know how I can change the porosity of terracotta slip.

I would like a green colored one to be very porous, a blue one medium porous, an orange one less porous, you get the idea.

I was going to slip cast into plaster molds.

Any and all input is welcome at this point as I can't express the yawning chasm between my excitement to achieve this and the ability to do so. I have a very good idea on how to measure the flow rate once I have more control of the porosity.

Thanks in advance for any assistance.

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geremyh    0

porosity as in the flow of water through the walls of the terracotta vessel. They are called olla's

http://drippingspringsollas.com/about-ollas/

I have the thought that adding bentonite might help but I'm not sure how this would effect the casting, Or by using a different mix as a second slip pour. Or adding some fiber material such as fiberglass.

Thank goodness you've responded I started to become concerned with such little activity but I figured the real pro's are members here.

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bciskepottery    925

You can achieve different rates of porosity using the same clay body by firing the wares to different temperatures. For example, an olla fired to cone 06 will be more porous than one fired to cone 1, and the one at cone 1 will be more porous than one fired to cone 4. Those are just examples, you would need to test your olla at different temperatures to find out how porous they are at that temperature. But you would also have to test additions to the clay slip to get porous, more porous, most porous, anyway.

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geremyh    0

Thank you 

bciskepottery

Wonderful that such a simple mechanism can get me the results I desire, so long as I can control the firing temps and times. You touched on additives which is something I love to do, chemistry and mixing chemicals and the such. I have a background in the coatings industry (catalyzed varnishes, epoxies, lacquer, etc.)  What additives would be worth me investigating may I ask? It sounds like I would be over complicating things but knowledge is power they say.

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Why do you think bentonite would change the porosity?

 

You could try adding different sized pieces of sawdust that would burn out during the firing. Not sure how well this would slip cast. Then fire them all to the same low temp to keep the clays natural porosity.

 

I don't know if this would actually change how fast water passes through the wall, is that what you are going for? Three different speeds of watering?

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geremyh    0

Bentonite is used in well drilling to keep the walls of the well from collapsing while you drill. It is a clay, readily available and cheap so would be most compatible (afaik). Some instances say it is even used as a glazing ingredient, and since a proper glazing would make it impermeable, there might be something there worth trying. 

 

I like the sawdust idea which would increase the space available for water to pass through (brilliant idea honestly), the opposite of the bentonite concept. Since this isn't really a structural strength application I don't think I would have to worry about it weakening the vessel, within limits. What's most attractive about that idea is that a single temp would be required making home based manufacturing much more manageable. Yes that is the ultimate goal, to make 3 (or more) watering speeds. GPD (Gallons Per Day)

 

Also had an idea of just making  brush strokes of glazing before firing. If the vessel is half glazed then it would be half as porous as a fully unglazed, right? And would be an artful addition.

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Chris Campbell    1,087

I would also consider making it with a paper clay slip ... Strong at the greenware stage and porous when fired ... Plus you play with the paper addition % until you get the porosity right.

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Min    782

Just curious, if it's buried in the soil, who would see the glazing?  

 

 

that's off topic

 

sorry but I don't understand how that's off topic?

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Benzine    610

I've never heard of such a vessel, interesting. What kind of vegetation are they meant to water; flowers, vegetables, bushes/ trees?

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geremyh    0

Anything really. Designed to saturate the ground around the vessel supplying water to any plant, trees, veggies, shrubbery, etc and limit or reverse the effects of natural evaporation from the soil. Mostly for hot arid areas in Zones 8 and up like deep East Texas where I'm at. Effectiveness is varied and dependent on soil type. i.e. sand loam will drain faster with a smaller diameter of effectiveness, clay laden soil will have a larger diameter of effect underground.

@Chris Campbell et. al

  Do you think there would be an issue with rot, fungus, or mildew using paper products? 

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Pres    896

Paper in the paper clay burns out of the kiln before 500F. Therefore there would not be any rotting. I would be concerned that the clay would grow mold as is natural in that sort of environment-in the ground with water and organic matter settling into the container. However, if this is what you are looking for the Paper clay should work.

 

Years ago I made thrown pottery for raku that used pearlite as a filler to speed drying. This material also burned out in the kiln leaving a very porous form. I don't see why it would not be able to be use at mid to high range stoneware or earthenware temperatures.

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geremyh    0

i just need a quick fact check from you Pres. was that perlite or pearlite. the two are significantly different and from a quick google it looks like perlite is the substance i would want to use as it expands when heated. Whereas Pearlite is a metal alloy.

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Pres    896

Yes, it is perlite. I was not thinking of the spelling, just remembered the name.

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Just curious, if it's buried in the soil, who would see the glazing?  

 

 

that's off topic

 

sorry but I don't understand how that's off topic?

 

Don't mind me- I am sleep deprived because I waited until 2am for my kiln to shut off…. but i can't help but constantly re read this and LOL!!!!!  I have never seen anyone say that something was off topic on this forum, we are distracted ADD artists and tend to welcome misdirection in the posts! AHAHAHA

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Benzine    610

The Moderators and Administrators here, do a good job, of moving the topic along, in case it goes on a tangent. This is a community, and posters are treated as peers. There isn't a super strict adherence to a topic, to the point, that something slightly off the subject line, will get a person warned, or post deleted. The only time posts become an issue, is when someone insists on personal attacks/ general disrespect.

 

The question posed, was nowhere near, being as off topic, as some discussions have gotten. I feel it was a valid question, in line with the topic, "Why glaze something that will rarely be seen?" Beyond that, why "waste" glaze on a portion of the object that will be burried below the ground? I do agree, some glazing would help the overall aesthetic, but why not just glaze the portion that will be above the surface? Also, a glaze would effect the porosity, as it does seal the clay, even if just a bit.

 

Just some thougts.

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geremyh    0

and I feel I addressed the question before it was even asked. 

 

 If the vessel is half glazed then it would be half as porous as a fully unglazed, right? And would be an artful addition.

 

So I was between a rock and a hard place. go off topic to explain it, or ignore it knowing full well it was gonna come back to bite me. I chose the later. I see your point though in that maybe I was a little too hard nosed.

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well i guess it's time for me to address the issue. Many admins and moderators of forums HATE off topic stuff in threads. It is frowned upon because it makes it difficult for people to find the information they want and need and expect to find in a thread. Also it costs money to store threads on the servers they pay for and I can say with some certainty they don't want to pay for someone's ramblings.  The topic is porosity of clay and there is some good info here regarding that topic. If you want to talk about the importance of something being glazed when it's going to be buried in the ground then I feel I'm not talking to actual artists who wish to beautify and better this world through their chosen medium with expressive talents. Just here to push my buttons for the sake of getting a reaction. Now that I've gotten the information I need by all means let's talk about 'if it's buried in the soil, who would see the glazing?  '

 

I'm a business owner and a consumer too. Take this image for instance.Nanny.jpg

That's functional, utilitarian, and ugly to me. Without discussing my ACTUAL designs I would much rather buy the one on Home Depot's shelf that had some artistic glazing instead of the one in the image above. Maybe some nice blue streaks or who knows just something colorful. As a CEO, marketing exec, and the CFO it's important for my product to stand out from the others. So here I am in a meeting and someone shows me a mock up, you know what I'm going to say? "Put some colorful stripes or something on that thing and then get back to me." 

Now someone paid good money says to me "But it's going to be buried in the ground, nobody is going to see it."

Then I say "If I need to explain why I want some colors on that terracotta then don't show up for work tomorrow."

 

I have to say, I would much rather admit I'm buying a cheap product than purchase a decorated product, likely at a higher price.

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Benzine    610

and I feel I addressed the question before it was even asked. 

 

 

If the vessel is half glazed then it would be half as porous as a fully unglazed, right? And would be an artful addition.

 

 

So I was between a rock and a hard place. go off topic to explain it, or ignore it knowing full well it was gonna come back to bite me. I chose the later. I see your point though in that maybe I was a little too hard nosed.

To be fair, you addressed the point one post before, and only several minutes before. mss may have not seen, that the thread had been updated.

 

In terms of the glazing, how much of the vessel will be visible, above the ground? I can honestly see, that an unglazed brown, reddish-brown being desirable, if a person doesn't want the vessel to stand out. Are you planning on using the wine bottles as well?

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bciskepottery    925

Having followed the link to the olla that was buried in the garden bed with only the top of the neck visible, I was a bit baffled by the idea of glazing or using glazing to affect the rate of water seepage into the soil. Fast forward to the pix of the plant nanny device, and the idea of glazing (or using colored slip, engobes, or terra sig to add some color interest becomes more apparent. Maybe others were a bit like me and had trouble imaging the glaze part because we were thinking of a large bulb under the soil.

 

That said, glaze on the top is an option, but if you only do the part that is above ground, it will not affect porosity or the rate at which the water seeps. Other options for adding color/interest are colored stains or engobes; one advantage there is you could probably just do a single fire and save time/money vs. glazing which would likely involve two firings (bisque and glaze). At low fire temperatures, you might be able to get away with applying decals. With a glaze, or any colorant, you need to think about the potential for the durability of the glaze/colorant and whether or not it could leak into the soil and become a contaminant.

 

As a consumer, I like the plain terracotta; don't have to worry about colors clashing with type of flowers/plant in the planter. Plus, I want the focus on the flower/plant, not the pot/water feeder. Just my preference. As I've learned making vases, some folks like a muted colored vase, others want bright colors. So, I make some of each.

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