Newly discovered Clay in backyard - Firing results

[cafedunier]

Hi there, Im a brand new potter, having found grey clay in my back yard. I slurried the clay and strained it through a metal kitchen sieve and let the water evaporate. I gave a chunk of clay to a friend who has a kiln and he fired it to cone 5. Edit: It was blobby to begin with and it didnt melt. It just got shiny. This is the result and I really need your input and opinions as to what kind of clay I have here. Its very shiny and I did not glaze it.  The light brown picture is when it was bisque fired to cone 06 and the dark brown pics to cone 5.

 

he said it picked up some kiln wash off of the shelf. It was just a random chunk of wet clay that we dried out and fired.

 

Edited November 21, 2022 by cafedunier

[Hulk]

Hi cafedunier,

Welcome to the forum!

Looks overfired at Cone 5, well melted.

While waiting on wild clay experts to weigh in, please post images of the clay as found (wet and dried), describe its working properties - how plastic, does it crack during drying, and (approximately) where found. 

[cafedunier]

it kept its shape perfectly.. it was blobby to begin with. The cone indicates it is underfired, so its weird. It doesnt crack much at all while drying and I found it near a creek.

Edited November 21, 2022 by cafedunier

[cafedunier]

25 minutes ago, Hulk said:

Hi cafedunier,

Welcome to the forum!

Looks overfired at Cone 5, well melted.

While waiting on wild clay experts to weigh in, please post images of the clay as found (wet and dried), describe its working properties - how plastic, does it crack during drying, and (approximately) where found. 

OK I edited the original post to include a picture of the chunk when it was bisque fired. it didnt lose its shape the whole process 

[Min]

There is a lot of leda / quick clay in the Ottawa Valley, a quick Google search brings up quite a few documents and geological surveys done in the area. Does the location of where the clay was dug up match up with locations such as those in this link? Like @Hulk said it looks overfired at cone 5, would probably need to either fire it lower or amend it with other materials to fire at midrange. How plastic is it? Can it be made into a coil and bent around your finger without cracking? 

I started a thread on Wild Clay here, might be something in the links in that thread that you find helpful.

Edited November 21, 2022 by Min

[cafedunier]

6 minutes ago, Min said:

There is a lot of leda / quick clay in the Ottawa Valley, a quick Google search brings up quite a few documents and geological surveys done in the area. Does the location of where the clay was dug up match up with locations such as those in this link? Like @Hulk said it looks overfired at cone 5, would probably need to either fire it lower or amend it with other materials to fire at midrange. 

No, I found it in Northern Quebec. You are saying its over fired, but why are the cones not bent all the way over, indicating that its not fired to maturity?

[Roberta12]

There is a potter in Utah who digs clay in his backyard and uses it as a glaze, maybe you could say an overglaze effect.  Aaron Ashcraft.  I have several pieces of his pottery and have taken a ws from him.  It's interesting what that wild clay does to his glazes.

 

 

[Min]

1 hour ago, cafedunier said:

You are saying its over fired, but why are the cones not bent all the way over, indicating that its not fired to maturity?

Common Orton cones range from cone 022 (thats zero twenty two) approx 1080F up through cone 14 approx 2530F. Bisque firing is usually done between cone 08 and 04 if the clay is going to have a higher glaze firing. (exceptions in there but generally). Cone 5 might be what your friends clay matures at but it's not what your found clay matures at. Firing clay to it's maturity ensures you will get as strong a clay as possible. Typically potters fire to within 3 ranges, lowfire (approx cone 04 up to cone 01), midrange (around cone 4-7) and highfire (approx cone 9 - 12). Your found clay looks like it will fire to maturity in the lowfire range. What cone is optimum will take firing samples of it in the lowfire range. First link in that thread I posted above will help in testing your found clay.

1 hour ago, cafedunier said:

I found it in Northern Quebec

Have a look at some Geological Survey maps of the area in Quebec it is from.  Might not be necessary but it could be interesting. 

[Kelly in AK]

Definitely starting to melt, that’s the shine. It might make a nice cone 6 glaze if you add some frit to it. You’ll have to do what @Min said and fire samples at different temperatures to find out what cone it matures at. That’s if you want to make pots out of it. Other basic tests, like for plasticity and shrinkage, help you decide what you can do with it or if it has to be adjusted with other ingredients to work. For example, a lower firing clay could be mixed with a higher firing one to get a mid-range clay body. 

It’s cool you found clay right in your backyard!

[oldlady]

could this be a vein of Albany slip clay that made all those dark brown teapots and electrical thingies on electric wires we drive under?

[Kelly in AK]

I have to admit @oldlady, that’s the first place my mind went! Northern Quebec is a little ways from Albany, but the earth don’t care. Could be the same stuff. If a pot’s antique and dark brown, it’s Albany slip. Potters all the way down in North Carolina would trade for it, way back in horse and carriage days mind you, to make their “frogskin” glaze.

Whatever the case @cafedunier, it may be as useful as a glaze ingredient as it is a clay body. 

[suetectic]

8 hours ago, Kelly in AK said:

it’s Albany slip

some of the secondary glacial clay or silt over here fires to a nice brown slip glaze on their own at cone 10. I imagine you have secondary clay in silt deposits in Alaska as well

Plainsman also markets Alberta slip as an alternative to Albany.

some secondary marine clays work well at cone 10 too

Edited November 22, 2022 by suetectic

[cafedunier]

12 hours ago, Kelly in AK said:

I have to admit @oldlady, that’s the first place my mind went! Northern Quebec is a little ways from Albany, but the earth don’t care. Could be the same stuff. If a pot’s antique and dark brown, it’s Albany slip. Potters all the way down in North Carolina would trade for it, way back in horse and carriage days mind you, to make their “frogskin” glaze.

Whatever the case @cafedunier, it may be as useful as a glaze ingredient as it is a clay body. 

well I have a ton of research to do to understand what you all are talking about, being a new potter, you are speaking a foreign language lol. One question... I found a guy to fire my stuff, although I pay to have it done. He is willing to fire samples at different cones, but how on earth do I determine what cone it matures at? Does it have a certain look? Feel? how do I know for sure?

[PeterH]

1 hour ago, cafedunier said:

but how on earth do I determine what cone it matures at?

This is a very informative site:
Maturity https://digitalfire.com/glossary/maturity

[BobMagnuson]

Instead of figuring out where the clay "matures", why not just use it for terracotta?  If it's plastic enough make pots, handmade or thrown, firing to around cone 04 often makes a beautiful clay body.  It won't be vitrified, but could be great for flower pots or sculpture.  Otherwise, a 50/50 mixture with wood ash will probably make a decent stoneware glaze.

[glazenerd]

The term is pyroplasticy: caused by low alumina. (16% alumina would be my guess). Pyroplasticity can be compounded by naturally occurring fluxes. If you want to use it as a clay body; then you need to add 20% kaolin (any kind) to raise the alumina level. Kaolin has 37% alumina typically. It could be used as a slip, but like glaze: low alumina levels makes it unstable. It could be used as a glaze with low levels of flux additions at cone 5. However, low levels of alumina will make it unstable.  Using it as terra cotta at cone 04 (as mentioned above) is the best option.  You have iron disulfide bearing clay; which goes brown once you get above cone 3 or so.

Tom

[suetectic]

12 hours ago, BobMagnuson said:

Instead of figuring out where the clay "matures", why not just use it for terracotta?  If it's plastic enough make pots, handmade or thrown, firing to around cone 04 often makes a beautiful clay body.  It won't be vitrified, but could be great for flower pots or sculpture.  Otherwise, a 50/50 mixture with wood ash will probably make a decent stoneware glaze.

even a simple 3124, silt, tin oxide makes a great glaze at cone 6.

some silts show promising oil spots on their own and with additions get even better. high fire oxidation though

I used to work with a very nice tenmoku using ~70% silt...iron saturates too in oxidation

There were areas of a triaxial with wood ash and silt that indeed showed promise at ^10 in reduction

i didn't really mean to blurt all this out but wanted more to support the suggestion there are indeed many decent glazes to be found using these silts.

 

 

[Min]

All these suggestions of what to do with your found clay are great! 

Given that you are brand new to working with clay I would think about what your goal is for this clay, what do you want to do with it? How much time, if any,  do you want to spend testing modifications of it? 

[cafedunier]

On 11/23/2022 at 11:16 AM, Min said:

All these suggestions of what to do with your found clay are great! 

Given that you are brand new to working with clay I would think about what your goal is for this clay, what do you want to do with it? How much time, if any,  do you want to spend testing modifications of it? 

Thank you everyone for your insights! As I progress, I will let you know how the pots turn out. Still in the testing phase.