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Super Amateur Needs Help With Porosity

porosity terracotta slip

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#1 geremyh

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Posted 21 May 2014 - 06:18 PM

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.



#2 Chris Campbell

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Posted 22 May 2014 - 07:51 AM

I don't think you are using the right word to describe what you want. What do you mean by "porosity"?

What are you trying to achieve?


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#3 geremyh

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Posted 22 May 2014 - 08:22 AM

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

http://drippingsprin...om/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.



#4 bciskepottery

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Posted 22 May 2014 - 08:44 AM

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.

#5 geremyh

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Posted 22 May 2014 - 10:25 AM

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.



#6 High Bridge Pottery

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Posted 22 May 2014 - 12:03 PM

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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#7 geremyh

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Posted 22 May 2014 - 12:39 PM

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.



#8 mss

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Posted 22 May 2014 - 12:47 PM

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



#9 geremyh

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Posted 22 May 2014 - 02:34 PM

that's off topic



#10 Chris Campbell

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Posted 22 May 2014 - 08:12 PM

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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#11 Min

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Posted 22 May 2014 - 08:51 PM

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?



#12 Benzine

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Posted 24 May 2014 - 08:13 AM

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

#13 geremyh

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Posted 24 May 2014 - 11:31 AM

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? 



#14 Pres

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Posted 24 May 2014 - 05:37 PM

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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#15 geremyh

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Posted 24 May 2014 - 07:13 PM

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.



#16 Pres

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Posted 24 May 2014 - 10:40 PM

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


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#17 Rebekah Krieger

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Posted 27 May 2014 - 02:18 PM

 

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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#18 geremyh

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Posted 27 May 2014 - 02:56 PM

deleted by poster



#19 Benzine

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Posted 27 May 2014 - 03:54 PM

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.
"Anything worth believing, is worth questioning"

#20 Rebekah Krieger

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Posted 27 May 2014 - 04:27 PM

LMAO!!!! :D 


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