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JohnnyK

What Happened Here?

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Here is an interesting happening...

I recently fired about a dozen of these "flowerpot gremlins" in a bisque/glaze firing to ^04.

The dark red on the right was done with 2 coats of pure red iron oxide. The strange looking one on the left was done with 2 coats of red iron oxide and 3 coats of ^06 translucent matte glaze.  Right came out pretty much as expected, but Left was a total surprise!

The "matte" finished glossy and the color just blew me away.

Any suggestions as to what might have happened. The clay was a ^5 B-Mix w/o grog.

JohnnyKpost-17674-0-55919000-1486494044_thumb.jpg

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The matte glaze may have cooled too quickly, or it was over-fired. As for the iron, it looks exactly as I would expect under a glaze. The iron is taken into the glaze and diluted. You can see the dark areas where it's going black, which is where the iron is on thicker. It takes a lot of iron to go dark under a glaze when firing in oxidation. I used to use a 10% iron slip in reduction, I use a 22% iron slip in oxidation to get the same darkness. Personally, I would use an iron slip rather than straight iron. It's easier to get an even application, and won't go metallic and overload the glaze when thick.

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Thanks for all your input! We'll call this one a test. The next "test" will happen when I do a ^6 firing to see what happens to the dark red ones.

If I want color, I will stick with underglazes and clear coats at ^06.

JK

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Was that one in a hot spot in Kiln??or near elements?

 

They were spread throughout the top shelf away from the elements...

The top shelf was a half cone hotter than the bottom of the kiln according to my witness cones.

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The top shelf was a half cone hotter than the bottom of the kiln according to my witness cones.

 

Which is normal for most kilns. I learned along time ago to mix crystalline glaze for the entire kiln load and save the end of the batch for the bottom shelf of the kiln. I then added additional flux for that 1/2 cone colder spot. Actually I use a PH meter, and adjust the PH from 10.50 on the top, to 10.75 for the bottom shelf. Then again most glazes are not that picky. If you are dealing with some that are; this is one simple way to deal with them.

 

Nerd

 

By the way, if your clear has zinc in it: that will also play into bleeding (fluxing) out the color of iron.

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