Jump to content

Recommended Posts

My mother lived in Valdez Alaska from 75 to 89.  At one point she rowed a boat out to an island dug up a massive amount of clay took it home washed it.  She was not a potter but rather used it to pour into ceramic molds.  It is a black clay that turns red when fired.  I am an intermediate potter using a potters wheel.  My questions are... has anyone ever worked with it in pottery?   How does it fire?  At what cone does it fire?  I have thrown one small pot with it but have not fired it yet.  Any information that I can get about this clay would be greatly appreciated.  

 

Share this post


Link to post
Share on other sites

hello, welcome, hope you find an answer.

i would suggest that you treat it as a very low fire clay.  if you have a bisqued bowl that is larger than what you have made, you might try firing the piece inside that bowl at the lowest cone you can manage.  put a lid on the top, a bisqued plate would probably do.

  it would be safer to make test strips and fire them individually at differing cones but that takes time and several firings.  it is safer and would give you a better idea of what you have.

you may have the clay that messed up a kiln so badly that people thought it was covered in chocolate.  see the recent post by callie beller diesel about clay disasters.

Share this post


Link to post
Share on other sites

The secondary clays/silts I've known fire to a 10 and resemble a nice albany/alberta slip with some oil spotting in oxidation.

Lots of nice possibilities as far as glazes go but no so much for throwing bodies.

Secondary clays like your marine clay can work as a body at low temperatures but they lack the plasticity of a primary clay used in throwing bodies.

Edited by C.Banks

Share this post


Link to post
Share on other sites

I found a nice page that explains clay in a useful way  : https://sites.google.com/site/meeneecat/educational-materials/clay-types-geological-origins-working-properties-gccceramics

You need some of this clay to experiment with- make samples that are all the same size and test fire at different temperatures with another scrap of broken pottery  underneath to protect your kiln shelves in case of a  meltdown! aka as per instructions above in previous answers.

Edited by terrim8

Share this post


Link to post
Share on other sites

Here is an approach, recycled from some earlier threads on exactly this topic.

I assume you have access to as much of this clay as you want. If not, forget about it. Unless the material is so important to you (eg sentimental value) that you are willing to go through all the work just to be able to use it a few times.

If you work at stoneware temps, first step is to fire a chunk to stoneware in a small bowl. Do not bother with other temperatures since you likely do not work at those temperatures anyway. Do not sieve or clean the clay except to get rid of large rocks, roots or sticks and other obvious debris (in any case not more than 12 mesh). Just fire it mostly raw.

If it turns into a bubbly molten mass in the firing, put it on a back shelf (carefully labeled) and forget about it until you have NOTHiNG else to do and want to kill a lot of time for maybe something you can use.

If the chunk remains intact then you have something to work with. It is either just right (a 1 in 100 event) or (more likely) somewhat refractory, but either way you have a path forward to find this out.

Next step would be to clean the clay to a level you are likely to be able to (and want to) replicate if you start to use it in some considerable volume. No use sieving to 100 mesh to run tests if you are unlikely to do that for every bit of it going forward when you actually start to use it. The chemistry and behaviour of the clay will almost certainly be different in these two cases.

Then make test bars which you will want to weigh wet, bone-dry, bisqued and high-fired to get an idea of Loss on Ignition. You will also want to measure shrinkage by measuring the bar (or some markings on it) at all stages along the way. Finally, if you want the body to be usable for functional ware, you will need to boil it for a couple of hours, then let it sit in the water for a day, and then reweigh. This will give you an estimate of porosity, or how much water the fired clay absorbs.

As you are going through this process, gather this information for some commercial clay bodies that you actually use (from the spec sheets from the manufacturer) and compare.

At the end of this, you will know if your clay is 

a) the holy grail: stoneware out of the ground. If you get this, pop the champagne corks.

or B) a refractory clay that will need some additions to be usable in the rest of your ceramic activities. But that is a whole nother chapter.

Share this post


Link to post
Share on other sites
5 hours ago, curt said:

Here is an approach, recycled from some earlier threads on exactly this topic.

I assume you have access to as much of this clay as you want. If not, forget about it. Unless the material is so important to you (eg sentimental value) that you are willing to go through all the work just to be able to use it a few times.

If you work at stoneware temps, first step is to fire a chunk to stoneware in a small bowl. Do not bother with other temperatures since you likely do not work at those temperatures anyway. Do not sieve or clean the clay except to get rid of large rocks, roots or sticks and other obvious debris (in any case not more than 12 mesh). Just fire it mostly raw.

If it turns into a bubbly molten mass in the firing, put it on a back shelf (carefully labeled) and forget about it until you have NOTHiNG else to do and want to kill a lot of time for maybe something you can use.

If the chunk remains intact then you have something to work with. It is either just right (a 1 in 100 event) or (more likely) somewhat refractory, but either way you have a path forward to find this out.

Next step would be to clean the clay to a level you are likely to be able to (and want to) replicate if you start to use it in some considerable volume. No use sieving to 100 mesh to run tests if you are unlikely to do that for every bit of it going forward when you actually start to use it. The chemistry and behaviour of the clay will almost certainly be different in these two cases.

Then make test bars which you will want to weigh wet, bone-dry, bisqued and high-fired to get an idea of Loss on Ignition. You will also want to measure shrinkage by measuring the bar (or some markings on it) at all stages along the way. Finally, if you want the body to be usable for functional ware, you will need to boil it for a couple of hours, then let it sit in the water for a day, and then reweigh. This will give you an estimate of porosity, or how much water the fired clay absorbs.

As you are going through this process, gather this information for some commercial clay bodies that you actually use (from the spec sheets from the manufacturer) and compare.

At the end of this, you will know if your clay is 

a) the holy grail: stoneware out of the ground. If you get this, pop the champagne corks.

or B) a refractory clay that will need some additions to be usable in the rest of your ceramic activities. But that is a whole nother chapter.

 

5 hours ago, Denice said:

If you decide not to go through the process of testing your clay,  you can always think how amazing your mom is that she dug it up and figured out how to use it.    Denice

Thank you,  Sorry I don't understand this site yet.  Good advice from many.  I know my mother did some slab pieces with this clay.  I just made a second mug and can't wait for it to fire.  It was a little harder to work with, it took quite a few try's.  It would be nice to be able to upload some pictures after I fire them.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×

Important Information

By using this site, you agree to our Terms of Use.