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Slip casting mug crack with hot water :(


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Hi!

A customer reported that a mug they purchased from us cracked with hot water… it’s a slip cast mug.

Not sure what caused the problem? We also have heard *ping* sounds for a few mugs when hot water was poured in. This only happened for our slip cast mugs but not on our wheel-thrown ones (with the same glaze). Please help!

best,

Garbo 

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it could be tension with the glaze interior exterior -Are they the same or different?

also the straight wall where it hits the flat bottom may be a stres point -I have seen this before.A more rounded thicker wall may help

You need to hot water test your forms before selling them from this point forward

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Wow, this is one of my worst nightmares. Shivering is the other. I really look forward to the responses on this.

 I haven’t had this experience personally but know a couple people who have. One was experimenting with a borax wash on bisque ware. Pots were glazed only with a liner then soda fired. The other was using a commercial clay she had used before without problems (New formula, perhaps?  Bad batch? She got a refund.). Both had the “Cracked with hot water” issue. 

Anyway, I’d like to know more about the clay body and how it was fired before I hazard any guesses on the cause. 

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Ive found out thru experience thats its not the glaze fit but rather the clay body that cant handle the sudden temp shock. Thru research and long conversation with Tony at digitalfire we came to the conclusion thatthe clay body I was using had an unusualy high amount of silica.... micro crystalline silica.  A change in the Hawthorn clay ore body prooved to be the culprit.   This led me to completely change the clay body Im currently making and using now.  With the clay body I have now I can take a mug straight from the freezer and pour in boiling water with no detrimental effects...

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10 hours ago, grumpykidstudio said:

This only happened for our slip cast mugs but not on our wheel-thrown ones (with the same glaze).

More info needed.

- Which claybodies? 

- Glaze recipes?

- Is the outside glazed?

- Any new claybody batches or glaze ingredients?

- What testing do you do on your glazes and claybodies?

 

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On 9/22/2022 at 12:04 PM, Min said:

More info needed.

- Which claybodies? 

- Glaze recipes?

- Is the outside glazed?

- Any new claybody batches or glaze ingredients?

- What testing do you do on your glazes and claybodies?

 

The slip is stoneware slip (https://www.sial-canada.com/en/sial-3/stoneware-bsgres) and glaze is a commercial glaze (https://g9r3e8w7.rocketcdn.me/wp-content/uploads/msds/glaze/600T_Series_Glazes/601T2012.pdf

the outside is glazed as well, we are unsure about the new batch becuase that customer bought this mug half a year ago.

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15 minutes ago, Rae Reich said:

Your slip body looks like it self-glazed a little. The broken exposed areas are pretty shiny.  Is this a body made for the same firing temp as your throwing body?

I think it looks shiny because there was water in the mug. And yes! we fire it at cone 6 and it's meant for cone 6

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On 9/22/2022 at 9:33 AM, Russ said:

Ive found out thru experience thats its not the glaze fit but rather the clay body that cant handle the sudden temp shock. Thru research and long conversation with Tony at digitalfire we came to the conclusion thatthe clay body I was using had an unusualy high amount of silica.... micro crystalline silica.  A change in the Hawthorn clay ore body prooved to be the culprit.   This led me to completely change the clay body Im currently making and using now.  With the clay body I have now I can take a mug straight from the freezer and pour in boiling water with no detrimental effects...

oh wow....that would be good to know! we have no idea what is in the clay but we bought it from https://www.sial-canada.com/en/sial-3/stoneware-bsgres 

sadly we just bought 50 boxes more before this happened... guess we will just need to test all the mugs with hot water first now!

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On 9/22/2022 at 1:53 AM, Mark C. said:

it could be tension with the glaze interior exterior -Are they the same or different?

also the straight wall where it hits the flat bottom may be a stres point -I have seen this before.A more rounded thicker wall may help

You need to hot water test your forms before selling them from this point forward

hi! the glaze is the same on the exterior and interior... it seems like the case only with our slip cast mugs but not wheel thrown ones... 

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On 9/22/2022 at 3:08 AM, Kelly in AK said:

Wow, this is one of my worst nightmares. Shivering is the other. I really look forward to the responses on this.

 I haven’t had this experience personally but know a couple people who have. One was experimenting with a borax wash on bisque ware. Pots were glazed only with a liner then soda fired. The other was using a commercial clay she had used before without problems (New formula, perhaps?  Bad batch? She got a refund.). Both had the “Cracked with hot water” issue. 

Anyway, I’d like to know more about the clay body and how it was fired before I hazard any guesses on the cause. 

it is the worst!!! we use https://www.sial-canada.com/en/sial-3/stoneware-bsgres for the slip.

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Put them in the coldest part of your freezer overnight then into the sink and straight away pour boiling water into them.

I just looked at the specs for that slip, it has a posted absorption figure of 2.89% which is high for ware like mugs. I would run your own absorption tests with it, ideally it should be below 1.5% for functional pots that will be used with liquids.

What's your glaze recipe? If it's a low expansion one then that combined with thin walled pots could be exacerbating the problem. Sometimes it's not just one thing that causes a problem but a combination of factors. 

Edited by Min
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6 hours ago, Min said:

Put them in the coldest part of your freezer overnight then into the sink and straight away pour boiling water into them.

I just looked at the specs for that slip, it has a posted absorption figure of 2.89% which is high for ware like mugs. I would run your own absorption tests with it, ideally it should be below 1.5% for functional pots that will be used with liquids.

What's your glaze recipe? If it's a low expansion one then that combined with thin walled pots could be exacerbating the problem. Sometimes it's not just one thing that causes a problem but a combination of factors. 

We use a commercial glaze https://g9r3e8w7.rocketcdn.me/wp-content/uploads/msds/glaze/600T_Series_Glazes/601T2012.pdf

not sure if that’s the problem… thank u for your help!!!!

 

 

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10 hours ago, grumpykidstudio said:

We use a commercial glaze https://g9r3e8w7.rocketcdn.me/wp-content/uploads/msds/glaze/600T_Series_Glazes/601T2012.pdf

not sure if that’s the problem… thank u for your help!!!!

 

 

Well that's unusual, they gave the exact percentages of each ingredient in the SDS. I plunked the recipe into Insight glaze calc and the coefficient of expansion comes in at 6.8 so it isn't a low expansion glaze, can rule that out. 

I really would suggest doing your own absorption test though to have confidence you aren't using a slip that has the probability of having weeping / leaking pots. Link on how to do that here if you need it, about 2/3 the way down the page. 

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