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Hi everyone, 

Hobbyist ceramist  with a few years of experience here, but not so much glaze chemistry knowledge.  I make work at a studio in Germany since a few years and since the summer, we noticed a lot of new issues with various glazes used at the studio. Nothing seems to have changed a priory with the way we do things.  We fire with 2 different Rhode ecotop kilns at 1220 celcius. All ours work is made using a white stoneware clay from one distributor. We order commercial glazes from the same distributor and a few other glazes from another one. We've been using the same glazes for years and the same firing cycle as well. We received a new order of clay and glazes in August from our main distributor and since that, we started to notice an increasing amount of dunting. The issues are mainly with work from beginner students that are taking classes at the studio and that are perhaps applying glazes a bit too thick. This is something that happens regularly but didn't usually result in dunting before. Then recently, I also started to have shelling or slight shivering issue at the rims of cups on some of my own pieces when using one particular glaze. It's a matte transparent glaze I've been using for years and never had issues with.  Is it possible that it is the clay body that is creating all these new issues? What is the best way to trouble solve from here? I emailed both distributors so ask if they know of any changes with their products already ( waiting on an answer) but any other tips I can get from someone with more experience would be much appreciated! 

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2 minutes ago, Hulk said:

Hi Mimi!

Any chance you have some of the white stoneware from previous order(s) to compare against the new material?

Unfortunately, I do not. ( or if we do, it was mostly reclaimed and has probably been partially mixed with the new clay batch since) I purchased a bag of similar clay from a local art store yesterday and will try and throw with it this week as a test to see if the problem persist with a different clay body. 

Also, perhaps this would be good to share: I also notice a lot more small brown specs in the clay when fired compare to before. Not quite like speckle clay, but very small spots here and there. The body is still mainly white but looks dirtier then usual if that make sense? 

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Sounds like something has changed with the claybody. Could just be a poorly mixed batch. Show them examples of the flecks you are now seeing in the clay that weren't there previously. Keep track of the batch numbers of the clay you are testing. Worse case scenario is you will need to change claybodies.

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24 minutes ago, Min said:

Sounds like something has changed with the claybody. Could just be a poorly mixed batch. Show them examples of the flecks you are now seeing in the clay that weren't there previously. Keep track of the batch numbers of the clay you are testing. Worse case scenario is you will need to change claybodies.

Hi Min, 

Thank you. This is my intuitions too.

Right now, I am pretty concerned since I sometime I sell my pieces and now I am very afraid that more issues could arise with the pieces I fired in the past couple months since we got the new clay. I haven't noticed the issue with most of my cups, only a few. All the ceramics I made in the past weeks are now sitting on the shelves of my studio and I don't know what to do with them and if they are safe... Is there a way for me to test the previous batch for shivering? I know that it a problem that don't always show right away.   I spent a few hours knocking the rims of my last load of cups today since I heard you can "encourage" peeling that way....and can't really seem to trigger the shivering in the pieces that don't show it.

I will follow up when I hear back from the supplier  about the clay.

I will also test another body this week and see if that resolve my problem. 

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One one shivers they all CAN -you really need to stop selling them until you get this worked out as they are unsafe

Only a few means they all can or some can or you really may never know once they are in others hands.This is a unsafe situation for your customers. 

(I haven't noticed the issue with most of my cups, only a few.)

We all have gone thru it at least once in our lifetime.-it sucks

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1 minute ago, Mark C. said:

One one shivers they all CAN -you really need to stop selling them until you get this worked out as they are unsafe

Only a few means they all can or some can or you really may never know once they are in others hands.This is a unsafe situation for your customers. 

(I haven't noticed the issue with most of my cups, only a few.)

We all have gone thru it at least once in our lifetime.-it sucks

 

Hi Mark, 

Yes, I am very concerned and haven't sold any of the cups since I noticed the issue. I would not be able to sleep at night otherwise. I am just not quite sure if it is shivering since it is only happening with a few cups and no other objects ( larger vase, planters, etc.) using the same glaze and clay combination.  I definitely feel like something changed with the clay that is triggering all the issues ( as I mentioned, people working at the same studio are having issues with dunting as well) but I am wandering if maybe the issue is only showing on the mugs because I compress the rim too much.  

7 minutes ago, Mark C. said:

One one shivers they all CAN -you really need to stop selling them until you get this worked out as they are unsafe

Only a few means they all can or some can or you really may never know once they are in others hands.This is a unsafe situation for your customers. 

(I haven't noticed the issue with most of my cups, only a few.)

We all have gone thru it at least once in our lifetime.-it sucks

 

54 minutes ago, Min said:

Sounds like something has changed with the claybody. Could just be a poorly mixed batch. Show them examples of the flecks you are now seeing in the clay that weren't there previously. Keep track of the batch numbers of the clay you are testing. Worse case scenario is you will need to change claybodies.

 

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