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simatai33

Glaze shivering with Penn State Shino and Rod's Bod Clay

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Hello everyone! I am stumped on this issue and was wondering if anyone had any insight or advice on this. We opened our soda kiln a couple weeks ago and I had a problem with my work. I fired 64 pcs, most of which was Rods Bod clay body which also had some Red Iron Oxide slip decoration on it.  I used Penn State Shino that I mixed the day that I glazed. 60% of it had major shivering! The glaze was just crumbling off and some thicker areas coming off in large pieces, leaving a grey stony finish behind. Such a bummer! See video here: https://youtu.be/0cbd0eXvYII
 
Some things to note in this firing:
- No one else's work shivered, but no one else used Rods bod or PSS Shino.
- Pieces from previous firing that didn't make it in kiln and fired this time were ALL okay. They had been sitting for 6 wks and were Rods Bod with RIO decoration and PSS glaze.
- I fired over two dozen spoons with Takamori clay body and PSS glaze, and NONE of them shivered. There was some crazing.
- All my Rods Bod pcs with SF Shino or other glazes did not shiver.
- 5 sake cups that fired cold didn't shiver. 
- There was crazing on several pieces.
- Areas that got hit with a lot of soda on Rods Bod/PSS would shiver.
- I did rush the drying process of Rods bod, drying in the sun and did a 2 hour pre-heat when I bisqued.
 
I never had a shivering problem with Rods Bod and PSS  glaze until the last two firings, which make me wonder if it's a clay body  issue, a combo of clay body and glaze fit, or something happened in the glaze mixture. Or could it be the soda ash? I did find a discrepancy in our PSS recipe vs. the one from Liz Willoughby when I double checked today; we use  4.9 OM4 amount  instead of her 14.9 OM4 amt, and I wonder if that makes a difference in anything.
 
SODA ASH SPRAY RECIPE
1 lb soda ash to 1/2 gal water
 
PENN STATE SHINO RECIPE - LIZ WILLOUGHBY
14.6 Neph Synite
7.8 Soda ash (light)
9.7 EPK 
4.9 OM4
34.0 F4 feldspar
29.0 Spodumene
Edited by simatai33
clarification of PS SHino

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I'm going to venture that it is likely a glaze batch problem. Leaving 10% of your clay out is definitely going to affect the recipe, because you're missing a statistically significant percentage of your silica and alumina. Even without looking at glaze calc software, that leaves the recipe really oversupplied with all kinds of sodium flux, which would be exacerbated by adding yet more sodium of any kind when you sprayed. Sodium has a high coe, so the resulting shivering is logical. 

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6 hours ago, Min said:

Is the shivering only over the pots with iron oxide slip? Wondering if the slip bonded to the underlying claybody. 

Hi Min,

No the shivering is happening on areas on a couple Rods bods vessels that had no slip on it.

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6 hours ago, Callie Beller Diesel said:

I'm going to venture that it is likely a glaze batch problem. Leaving 10% of your clay out is definitely going to affect the recipe, because you're missing a statistically significant percentage of your silica and alumina. Even without looking at glaze calc software, that leaves the recipe really oversupplied with all kinds of sodium flux, which would be exacerbated by adding yet more sodium of any kind when you sprayed. Sodium has a high coe, so the resulting shivering is logical. 

Thank you for your insight Callie, much appreciated. I'll run some tests with the recipe that has more OM4 in it!  What is COE?

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4 minutes ago, terrim8 said:

coefficient of expansion - but the answer about leaving out 10% of the  ball clay OM4 is the biggie! It's like leaving out the eggs in a good cake recipe- the cake will be dry and fall apart.

State Penn or Penn State?

That's a great analogy! It's Penn State Shino:)

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If it is the OM4 discrepancy, then I wonder why it didn't shiver before in previous firings? Only in the last two firings, and only in combination with Rods bod clay. Does anyone recommend a better Shino recipe for soda firing?

 

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this is the Shino I use at cone 10.     Water/solids ratio is ~0.7 weight ratio.   Crackle, yes on some clay bodies.  Never observed shivering.

component    % wt
Soda Ash              8.1
Neph Sy             39.3
Spodumene     30.6
OM4                   17.2
EPK                       4.8
Total                  100

 

LT

 

Edited by Magnolia Mud Research

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Leaving the clay out is just asking for issues-thats one thing I would say straight away .

Rods bod is a high silica content body so that would also point to some issues

Shivering can also happen later so keep an eye on those yet to shiver down the road and do not sell them.

The crazing is showing you an issue -the shivering is screaming at you an issue.

The glaze thickness also looks really thick as well which also could be an additional issue

I might change bodies or test a new body and mix the glazes with the right amounts next time for sure.When making glaze double check all the measurements at least twice.

Edited by Mark C.

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On 4/10/2018 at 6:29 AM, Min said:

Is the shivering only over the pots with iron oxide slip? Wondering if the slip bonded to the underlying claybody. 

Hi Min,

Actually I did make a NEW batch of RIO slip for the last two firings which had the shivering.  It was a different recipe from the one that I used before. Here's the difference:

Fish Sauce 
Grolleg Porcelain  43.8
Minspar (200)  23.5
Silica  15.6
Bentonite  9.4
Pyrax  7.8
Red Iron Oxide  15
 
New RIO Slip
EPK  50
Silica  35
Custer Feldspar  25
Bentonite  2
Gersley Borate  10
RIO  15
 
However, a few pieces of mine had no RIO slip decoration on it, and they still shivered. I'm not very knowledgeable on glaze chemistry and so really appreciate your input and have always enjoyed reading your posts! Thank you!

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17 hours ago, Mark C. said:

Leaving the clay out is just asking for issues-thats one thing I would say straight away .

Rods bod is a high silica content body so that would also point to some issues

Shivering can also happen later so keep an eye on those yet to shiver down the road and do not sell them.

The crazing is showing you an issue -the shivering is screaming at you an issue.

The glaze thickness also looks really thick as well which also could be an additional issue

I might change bodies or test a new body and mix the glazes with the right amounts next time for sure.When making glaze double check all the measurements at least twice.

Thank you Mark! I will definitely do that and study up more on this. Since I like Rods bod so much, I think it's best to change to another type of Shino for soda firing.

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17 hours ago, Magnolia Mud Research said:

this is the Shino I use at cone 10.     Water/solids ratio is ~0.7 weight ratio.   Crackle, yes on some clay bodies.  Never observed shivering.

component    % wt
Soda Ash              8.1
Neph Sy             39.3
Spodumene     30.6
OM4                   17.2
EPK                       4.8
Total                  100

 

LT

 

Thank you! Much appreciated. Is there a name for that Shino?

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I think the lower ball clay is a red herring. John Britt recipe has OM4 at 4.9  Nan Rothwell transcribed from Liz Willoughby, cited in Studio Pottery Magazine June 2002 incorrectly and uses both versions of 4.9 and 14.9 (near the bottom of the page).

Low ball clay recipe compared to LT's recipe isn't much different, screen shot below, look at the box in the lower right corner. Your recipe is #1, LT's #2

5ace5295c10df_ScreenShot2018-04-11at11_17_35AM.png.97bccb3b2fdf80fea6bf386c4264ad2d.png

 

 

 

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