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twinmom

Clay Determination

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I've accumulated lots of clays with various firing temperatures, and I'd like to use all of these clays. But they are unlabeled as to type of clay or maturation temperature. What's a good, safe way to determine the firing temperatures of each of these clays? The clays range from earthenware to midrange and high-fire. Many thanks!

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I've accumulated lots of clays with various firing temperatures, and I'd like to use all of these clays. But they are unlabeled as to type of clay or maturation temperature. What's a good, safe way to determine the firing temperatures of each of these clays? The clays range from earthenware to midrange and high-fire. Many thanks!

 

Get a hold of a little high fire clay and make a couple pinch pots. Make sure what ever the other clay forms are will fit inside the pots acting as a reservoir if and when they melt. Fire at different temps till you at least know there range. Test test test. There is a ton of other tests you can do to find out how a clay will act.

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I've accumulated lots of clays with various firing temperatures, and I'd like to use all of these clays. But they are unlabeled as to type of clay or maturation temperature. What's a good, safe way to determine the firing temperatures of each of these clays? The clays range from earthenware to midrange and high-fire. Many thanks!

 

Get a hold of a little high fire clay and make a couple pinch pots. Make sure what ever the other clay forms are will fit inside the pots acting as a reservoir if and when they melt. Fire at different temps till you at least know there range. Test test test. There is a ton of other tests you can do to find out how a clay will act.

 

That's a good solution to protect kiln shelves. Thank you! But I still need to determine the maturation temperature. I'd like to know more than the melting point of the clays. It might be possible for, say, a Cone 5 clay to fire to Cone 10 without melting--but that doesn't mean it's the optimum temp for that clay. Do you or anyone else have any more ideas or resources? Thank you for your time.

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Do you want to be sure these clays will be fired correctly as far as being safe for functional ware or do you just want to be sure every clay body is fired to it's optimum temp for other reasons?

 

 

Most of my work is functional, so I want them to be safe for consumers.

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Chris brings up a good question. The tests at different temps and porosity tests will give you an idea of the clays mature range. For example you take a clay and fire to cone 4 and you test to find it has a 16% porosity then you fire it to cone 6 and it has a 8% porosity. So judging that you should be able to estimate your optimum temp and test from there. Always have high fire bowls as guards. It probably wont be that simple of values that drop half every two cones but you should understand where Im coming from.

 

Although in my search for utilizing raw materials etc one potter mentioned that a lot of commercial grade clays can actually be fired to extreme temps a lot higher than their cone rating. So back to Chris's question...what exactly are you aiming for?

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This is just my opinion from a business point of view.

Clay is cheap. Your time is expensive.

 

Testing all these clays to make sure they are safe for consumers is going to take you a long time.

You might have a secondary motive of really wanting to learn how to test them ... in which case, go for it.

 

But from a cost point of view, unless you are talking about hundreds of pounds of each clay I would just make some yard art and enjoy the experience rather than make myself crazy testing and recording every batch.

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This is just my opinion from a business point of view.

Clay is cheap. Your time is expensive.

 

Testing all these clays to make sure they are safe for consumers is going to take you a long time.

You might have a secondary motive of really wanting to learn how to test them ... in which case, go for it.

 

But from a cost point of view, unless you are talking about hundreds of pounds of each clay I would just make some yard art and enjoy the experience rather than make myself crazy testing and recording every batch.

 

 

Hi, Chris. You're probably right. It's the cheapskate in me--I just hate to see something go to waste. Maybe I'll take a minimal amount of time to get a general idea of whether a clay will melt at Cone 10 (with a high-fire container for safety, just to make sure my kiln shelves won't be ruined), without worrying about the other aspects of porosity, etc. Then I can, as you say, make "yard art" and be happy for the experience.

 

I appreciate all the comments received. Thanks, everyone!

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Chris makes a good point, it will take a lot of time to test all the clays, and that's time that might be better spent making salable items or teaching, or whatever you do with clay to make "dough."

If you have hundreds of pounds of each of these, it might pay, but it is much like reclaiming clay, it usually costs more than it is worth.

How much of these clays do you have? I have to admit, I would chafe at the waste of clay, but sometimes you have to "cut your losses."

 

(After I posted this, I saw that your post, above, had snuck in just before mine!)

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