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KJC1130

Would Reduction Firing Make Pottery Harder/stronger?

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Hi! I am super beginner in making pottery.

 

I'd like to make a pot thin but hard like metal. I've found a pot in a garbage looks like this

https://cookniche.com/Photo.aspx?name=MitchiburgCeramics&IDservice=11440

 

it seems like it has irons on the surface.

Would these irons make the pot harder? or is this only for decorating the surface? 

 

could you let me know any other ways to make a pot harder?

 

thanks!

 

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No. Firing to vitrification will make the pot strong whether it's fired in reduction or oxidation. However, how you measure 'strong' all depends on what type of test you're doing. Terra cotta is actually stronger than vitrified  stoneware according to one test.  Iron does not necessarily make the body stringer. In fact, too much iron will make it brittle.

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Being a beginner, I will try not to make my answer overly technical. <we shall see>

 

The article in your link referred to "iron rich" natural clay: which would translate to a fireclay with 5-6% naturally occurring iron. You can make additions of iron, but as Neil pointed out: when it crosses a certain limit it becomes brittle.  The article also indicated a temperature of 2150F, which would translate to a cone 5 1/2, assuming an extended hold was observed. Iron has much less fluxing capacity at these temps as compared to a cone 10 firing. Reduction does enhance the fluxing ability of iron, again more so in a cone 10 firing. The "iron crystals" you see on the surface are from an extended hold around 1950F (40-60 minutes).

 

You would have to know clay formulation to make a custom body to meet your specific needs. A cone 6 body with 26 to 30% alumina would produce a body you could throw thin, and yet have high fire strength. It would also need a higher percentage of high SAS ball clay for increased green strength and modulus of rupture. High formula limits of alumina in glazes, and high percentages of alumina in a clay body = strength.

 

I am not overly familiar with commercial bodies, I mix most of my own clays. There are several on the forum that are fairly versed on the various bodies available: I am sure they could steer you towards something in your goals.

 

1. High Iron  2. high alumina 3. higher plasticity --- would be your criteria. 

 

Nerd

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From Mitch Iburg's Etsy site . . .

 

Thrown native California clay

Wood Fired to 2150 degrees F.

Cooled in a reduction atmosphere

No applied glaze

 

Made from an iron rich earthenware harvested near Comptche, CA and used without any additions. This clay is formed by erosion of sedimentary rocks belonging to California's Northern Coast Mountain Range - approximately 60-150 million years old. Screened only to remove large stones and organic matter. Small stones of shale, sandstone, and mudstone in the clay melt out during the firing, creating minor protrusions on the surface and retaining a visceral reference to the landscape and history of its origin.

 

Fired to 2100 f. in a wood burning kiln for 42 hours using Ponderosa Pine and Manzanita. Each piece was loaded in a small bed of rice hulls - a local agricultural byproduct which, when used in the kiln, prevents the work from sticking to the shelves and creates iridescent color and textural variation.

 

All color variation results from naturally occurring iron in the clay and its reaction to temperature and oxygen throughout the firing.

 

Water Tight, Food Safe

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