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Messing with geology in glazes?


Andere
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I'll start by saying I know nothing- I have two housemates with school backgrounds in ceramics and am helping catalyze their ceramics studio dreams as we wait for covid to be over.  My housemates are hoping to make functional ware, bowls and mugs and the like with commercial clays and glazes while I'll be off playing with rocks and dirt and seeing what happens when they get fired. 

We live in a very geologically rich region with vibrantly colored soils ranging from purple volcanic tuff, black, blue and yellow phyllite, celadonite deposits, red paleosol, yellow and green volcanic ash deposits, large bentonite domes and perlite flows. Lots of natural clay, sticky and elastic as peanut butter, and feldspar sands along the roadcuts. The local hills have been inspected for mining potential and that analysis picked up trace lead, mercury, antimony, arsenic, gold, silver etc. etc. We're six miles downstream from what was one of the biggest cinnabar mines in the northwest (collapsed, literally, in on itself in the 1950's.) While subsequent surveys didn't pick up any notable cinnabar outside of the one volcanic plug that was mined, it does still occur in trace amounts throughout the region.

How likely is it that doing geology in the kiln is going to put mercury into my friends' coffee mugs? Is this a valid concern when working with and testing raw materials? (also has anyone fired agate in their clay and how did it turn out??) 

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Lead and arsenic are everywhere. Lead would be a big concern because it tends to accumulate in kilns. Claybodies are engineered or at least tested for workability, durability etc...., glazes contain clay, feldspar, etc..... The geology of the earth is  basically cone ten and potters have figured out how to reduce this to cone six and even cone 04. You knowledge in geology is a huge plus so experimenting could prove quite interesting. Measuring trace amounts? Not sure how you feel about that. For some it is a great adventure. Go slow, be cautious.

Edited by Bill Kielb
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The mercury should fume off at a relatively low temp. THAT would be a problem as the old time miners who used mercury  to catch their fine gold found out when they put it in a fire to get rid of the mercury and breathed the fumes. They had a host of health problems and had shortened lives.  Vent, vent vent.

I believe agate is a silicate, am I right? Ive put other silicates in my cone 10 kiln and they partially melted about as much as the feldspar rocks I tried. I have found that if I crush Andesite and add a bit of bentonite it will form a beautiful orange/gold glaze. 

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Not to be a total downer here but whatever you settle on, testing will be important. The trap here is what to test for and the devil is often in the don’t know what you don’t know details.

I have turned away tons of supposedly clean earth just as fill because the background levels of lead and arsenic exceed those of the site they were to be imported into as clean fill.

So to that, artists have a long history of using colorants only to find those same pose various levels of risk to human health. Cinnabar (vermillion) as many know it is just one such colorant. Comparative analysis of heavy metals is better than none but is it representative of the materials you are using, will be using, will be  excavated? In ceramics potters have found ways to encapsulate and make these items safer.

My opinion, this is a tough one unless you have studied the science of it which spans several disciplines including ceramic science and durability of same. Will your finished product be durable? How do you define it and how do you test durability?

Again vaporizing Mercury might be viable and extra ventilation might be an acceptable answer but my sense is it’s better to be cautious and try and figure out the things you don’t know or at least test the final product as thoroughly as practical.

Definitely doable, but definitely has a potential for elevated risk...................... Well gotta go now, turning away another 16 tons of supposedly clean fill that just tested too dirty to place ..........

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4 hours ago, Russ said:

The mercury should fume off at a relatively low temp. THAT would be a problem as the old time miners who used mercury  to catch their fine gold found out when they put it in a fire to get rid of the mercury and breathed the fumes. They had a host of health problems and had shortened lives.  Vent, vent vent.

I believe agate is a silicate, am I right? Ive put other silicates in my cone 10 kiln and they partially melted about as much as the feldspar rocks I tried. I have found that if I crush Andesite and add a bit of bentonite it will form a beautiful orange/gold glaze. 

Yeah, agate is a silicate with various impurities that give it pattern and color. Ground up it would probably go quite nice in a glaze, but I'm curious what would happen if it were sliced thin and fired. Hopefully melt and not explode! We're working out a vent/hood system before firing to funnel fumes out of the building.

3 hours ago, CactusPots said:

Check out Out of the Earth Into the Fire by Mimi Obstler.

 

 

 I will, thank you! Looks like a very interesting book. 

2 hours ago, neilestrick said:

If you have the numbers on the heavy metals that are found in the raw materials in your area, then you could compare those to the allowable limits in a certified non-toxic clay body. If it exceeds those limits, I'd pass on using them.

I will compare those numbers. I have a mine assay report from the mid 1950's. It's for a deposit of weathered-out clay and rhyolite a few miles away but similar overall geology; very minute amounts, far too small for commercial mining, but I wouldn't eat the dirt. Our drinking water tests pick up trace amounts as well, but so far all well under allowable limits for water systems. 

1 hour ago, Bill Kielb said:

Not to be a total downer here but whatever you settle on, testing will be important. The trap here is what to test for and the devil is often in the don’t know what you don’t know details.

I have turned away tons of supposedly clean earth just as fill because the background levels of lead and arsenic exceed those of the site they were to be imported into as clean fill.

So to that, artists have a long history of using colorants only to find those same pose various levels of risk to human health. Cinnabar (vermillion) as many know it is just one such colorant. Comparative analysis of heavy metals is better than none but is it representative of the materials you are using, will be using, will be  excavated? In ceramics potters have found ways to encapsulate and make these items safer.

My opinion, this is a tough one unless you have studied the science of it which spans several disciplines including ceramic science and durability of same. Will your finished product be durable? How do you define it and how do you test durability?

Again vaporizing Mercury might be viable and extra ventilation might be an acceptable answer but my sense is it’s better to be cautious and try and figure out the things you don’t know or at least test the final product as thoroughly as practical.

Definitely doable, but definitely has a potential for elevated risk...................... Well gotta go now, turning away another 16 tons of supposedly clean fill that just tested too dirty to place ..........

 

Oh gosh that sounds like fun. Folks think "if I didn't get it dirty it must be clean," and don't think about the smelters or orchards or whatever in the area forty years back.

The rhyolite necks are what the miners focused on, for cinnabar and gold. I'd love to get our phyllite deposits tested though. They weather into a really sticky clay in a variety of colors and have some pretty interesting mineralization; it's (labeled as) pre-cretaceous seafloor, far too metamorphic for fossils, but I would be curious about minerals and metals for both clay/craft purposes and for knowing if it's got rare earths. I wouldn't be making anything functional with local clays or soils, just small sculptural objects to see what things look like and how they hold up. I just don't want to contaminate the kiln if my experimentation in one firing might leach back into my friends' food-grade stuff on the next round! 

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On 12/14/2020 at 5:26 PM, Andere said:

I'll start by saying I know nothing- I have two housemates with school backgrounds in ceramics and am helping catalyze their ceramics studio dreams as we wait for covid to be over.  My housemates are hoping to make functional ware, bowls and mugs and the like with commercial clays and glazes while I'll be off playing with rocks and dirt and seeing what happens when they get fired. 

We live in a very geologically rich region with vibrantly colored soils ranging from purple volcanic tuff, black, blue and yellow phyllite, celadonite deposits, red paleosol, yellow and green volcanic ash deposits, large bentonite domes and perlite flows. Lots of natural clay, sticky and elastic as peanut butter, and feldspar sands along the roadcuts. The local hills have been inspected for mining potential and that analysis picked up trace lead, mercury, antimony, arsenic, gold, silver etc. etc. We're six miles downstream from what was one of the biggest cinnabar mines in the northwest (collapsed, literally, in on itself in the 1950's.) While subsequent surveys didn't pick up any notable cinnabar outside of the one volcanic plug that was mined, it does still occur in trace amounts throughout the region.

How likely is it that doing geology in the kiln is going to put mercury into my friends' coffee mugs? Is this a valid concern when working with and testing raw materials? (also has anyone fired agate in their clay and how did it turn out??) 

Sounds like you have a good handle on what's around you. Natural color gives some indication: "green ash" usually indicates calcium. "Sticky and elastic" indicates a specific type of humus (organic) called muck. Common for natural clay deposits to derive some/all their plasticity from Organics. Yellows typically indicate iron; while purple tends to be iron, with some titanium. The key word is functional: which sets the safety bar much higher. "Trace" toxins such as lead, cadmium, selenium, arsenic, and mercury are common in many Ceramic materials. Understand that "trace" by definition means below acceptable safety limits. 

Natural clay harvesting, and natural glaze materials are vastly more popular than most realize. This forum does not typically delve into those subjects in general. Threads on primitive firing and techniques can be found; but little on processing, testing, developing natural materials.

Tom

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8 hours ago, glazenerd said:

Sounds like you have a good handle on what's around you. Natural color gives some indication: "green ash" usually indicates calcium. "Sticky and elastic" indicates a specific type of humus (organic) called muck. Common for natural clay deposits to derive some/all their plasticity from Organics. Yellows typically indicate iron; while purple tends to be iron, with some titanium. The key word is functional: which sets the safety bar much higher. "Trace" toxins such as lead, cadmium, selenium, arsenic, and mercury are common in many Ceramic materials. Understand that "trace" by definition means below acceptable safety limits. 

Natural clay harvesting, and natural glaze materials are vastly more popular than most realize. This forum does not typically delve into those subjects in general. Threads on primitive firing and techniques can be found; but little on processing, testing, developing natural materials.

Tom

Thanks for this perspective! I will collect and post some of the muck, it's legendary for its sliminess and ability to swallow things. Cold bentonite and clay soil upwellings are a local landscape feature and when wet and active, occasionally eat cows. I have gotten my hands on a more recent and very thorough geological survey from the 1980's and am going through it for PPM data, but looking like it's all well below safe thresholds for both sedimentary deposits and native stone. Selenium, oddly enough, is not present in our area; animal feed is fortified with it as the deficiency in local forage gives them muscle problems. (Injecting a pig with selenium in solution is an interesting endeavor!) 

 

5 hours ago, C.Banks said:

If you are looking for book recommendations Natural Glazes: Collecting and Making by Miranda Forrest is one of the best out there, at least for glazes.

Thank you for the recommendation, have ordered a copy! 

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