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questions about tenmoku

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I do not have my own studio so I can do my stuff only when visiting the local beginners workshop at the local ceramic studio.

I did some experiments with tenmoku they had laying around. I was told I can use it on my ow risk because nobody had used it for long time.

I am trying to understand, what went "wrong" with the second patch.


I had some small cups ready to glaze and this is the result from first patch:





Second patch, I glazed and got fired few weeks later, looked completely different:





I am sure I applied the glaze same way as before.

I was assured that same program for firing was used as before.

Yes, the second stoneware had a bit thinner walls than one in #1 - can this be one of the causes for completely different outcome?

I am almost sure smile.gif that the ready mixed glaze in this can was way thinner than 2 weeks ago - can this be one of the causes for completely different outcome?


Any help is appreciated to figure out, what went "wrong".


Thank you.

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Looks like your second piece is over fired. The glaze is literally running off the pot. Was it placed in a hotter part of the kiln? Also, you get glaze runs if the glaze is applied too thickly. Could this be the issue? I know that you said the glaze was thin. It's a mystery.


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If these where glazed all at the same time then its the hotter firing area as in above post by TRJ if they where glazed at separate times its thickness issues with glaze or both.

Welcome to the wonderful world of ceramics -its always different-that you can bank on.



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What does the vessel look like on the bottom did it run?

If you noticed the blue is in the same place on both vessels, heavy and floating downward.

This is a very runny glaze. In your first test sample did you encounter the glaze being very runny and then opt for a partial glazing for your next test sample?

Also, glazing on the interior of a vessel maybe different on the exterior of the same vessel.

I commend you for testing you have learned a lot about this glaze. Keep going until you get it the way you want it. That blue is beautiful by the way.

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What cone and kiln type?



Not sure about the cone but it's probably 9-10 (looking at conversion chart) and we only have a electric kiln.


I did another run. I added no other glazes (like on 2 previous pictures) and the result is still not good. Fired glaze is mostly thin and ugly brown in most of the areas. (if it was only at the edge, I'd be happy - like on the first image)

I am almost sure now that the glaze is OK but it is just watered down so I can not get it thick enough on the bisque ware. I left the glaze can open so extra water can evaporate. Will do another test in few days do see what happens.


If you have a good deep black temmoku recipe for electric kiln at cone 9-10, let me know (must be possible to mix in EU!)

Edited by rakuu

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Yap I'm quite sure that your second piece was overfired. I think your glaze is running, it could be there is zink oxide in your glaze, isn't there?

The running / melt away could be depend on the thickness of the glaze. More thicker more running away the glaze. But I think that failure could be interested..

Another cause the wares in position near the flame, usually on the edge of the shelves. You can make the bricks wall on that edge..

Thank you for the attentions..

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