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Asmaa Aman-Tran

Clay chipping after bisque firing

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Hello everyone, 

I want to first thank you all for the endless advice and support to all of us. I have learned so much through this forum since I started my ceramic journey a few years ago.  

today, I come to you with an issue that I’ve been having with my red low fire and high fire clay. The low fire is a red Laguna with sand. The high fire is a dark Standard ceramic . I apply  OM4 terra sigilatta  to both clays and after the bisque firing to 05 , I notice chipping of the clay in random places on both clay bodies but not on all pieces. Sometimes it happens hours after unloading the kiln. I attached a picture on an example of the chipping . 
Did anybody experience this before. 

A6D128C3-DAA7-4C51-AC40-C1F0251911AE.jpeg

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Lime popping.

We had a Problem with Standard 420 doing it.

You could be picking up bits from the side of drywall, plaster bits, dirty sand, etc.

Doubt both clay bodies will have it originally.

 

Sorce

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Looks like 1 nodule for sure and maybe 2 smaller ones. If it's not  contaminants picked up while making the pots I wonder if both red clays are using a material from the same mine that is causing the issue. Which Standard and Laguna bodies are they? 

On 5/4/2020 at 6:02 AM, Asmaa Aman-Tran said:

Sometimes it happens hours after unloading the kiln.

Unfortunately lime pops can occur years after making the pots too as moisture turns the lime nodule into calcium hydroxide. 

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Thank you for your replies. I do wedge on drywall covered with canvas, now I suspect it might be bits of drywall boards. Although I did have the issue on some extruded shapes .  I’ll try to be more careful next time and see if the problem persists.  

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On 5/4/2020 at 9:49 AM, Sorcery said:

Lime popping.

We had a Problem with Standard 420 doing it.

You could be picking up bits from the side of drywall, plaster bits, dirty sand, etc.

Doubt both clay bodies will have it originally.

 

Sorce

Yes , it is actually the Standard 420 that I’m using, but I didn’t have this issue with a previous batch ... 

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3 minutes ago, Asmaa Aman-Tran said:

Thank you for your replies. I do wedge on drywall covered with canvas, now I suspect it might be bits of drywall boards. Although I did have the issue on some extruded shapes .  I’ll try to be more careful next time and see if the problem persists.  

Plaster is kind of like that.  Once it starts crumbling it gets everywhere!  One time I was drying some underglaze out on a plaster bat and everything I decorated with it popped, because I scraped the underglaze off and must have scraped a little plaster into it.  Grrr

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1 hour ago, Min said:

Looks like 1 nodule for sure and maybe 2 smaller ones. If it's not  contaminants picked up while making the pots I wonder if both red clays are using a material from the same mine that is causing the issue. Which Standard and Laguna bodies are they? 

Unfortunately lime pops can occur years after making the pots too as moisture turns the lime nodule into calcium hydroxide. 

It’s the Standard 420 and Laguna 104 

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2 minutes ago, liambesaw said:

Plaster is kind of like that.  Once it starts crumbling it gets everywhere!  One time I was drying some underglaze out on a plaster bat and everything I decorated with it popped, because I scraped the underglaze off and must have scraped a little plaster into it.  Grrr

 No good, I had this issue with corn starch That used on some slabs for texture. I applied terra sigilatta to the forms and it chipped of after firing and was blaming the sig.  It took me a while to figure out it was actually the cornstarch that made it chip off lol 

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Ohhh will cornstarch always do this? I've been using it in my handbuilding this week to keep it from sticking to the work surface (I ran out of space in my little studio). I thought it was a safe anti-adhesive.

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17 minutes ago, Juliagoolia said:

Ohhh will cornstarch always do this? I've been using it in my handbuilding this week to keep it from sticking to the work surface (I ran out of space in my little studio). I thought it was a safe anti-adhesive.

Will be fine if you're not applying terra sig :)

Terra sigilata goes on before bisque so the corn starch wasn't burned off

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You aren't alone in a problem with 420.

Just ask the lady who was raw glazing for months then bought a new kiln to fire em! Ouch!

I moved locations, and with fresh 547 (my favorite, no!) I have been noticing small bits pop from it. Not convinced it's the clay, but I know the clay is new, since the bags are different. (New bags at Standard recently) the Grog is definitely the same size, and I fear it has entered the 547.

I think the problem we ran into when trying to figure it out was that it IS Grog, that is causing it....already fired, so it was a stumper.

Most would only pop during a firing, and just tiny surface bits, almost like it's not lime. 

Perhaps something else slightly altering the clay around it?

I stopped using and recommending 420...

The clay.

 

Sorce

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On 5/7/2020 at 12:28 AM, Juliagoolia said:

Ohhh will cornstarch always do this? I've been using it in my handbuilding this week to keep it from sticking to the work surface (I ran out of space in my little studio). I thought it was a safe anti-adhesive.

It is safe for surfaces that intended for glaze, after bisque firing of course  or underglaze but not for sig . It creates a barrier and prevents the sig from adhering to the clay properly. 

Edited by Asmaa Aman-Tran

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