Jump to content
Sign in to follow this  
Patrick

"fitting" Glaze Shivers When Applied Thin?

Recommended Posts

Has anybody ever had a glaze that, when applied "normally" - think slow dip/double dip, 1/16" or so - does fine, but when applied thinner - quick single dip only - shivers at the edge of cup/bowl?  I've got 2 glazes that did it. Not sure if this is just a thickness issue or if my body/glaze fit is close enough to be ok thick, but shows some truth when applied thin.  Oh by the way: The firing was a pretty strong cone 10 reduction.  Not sure if that would change anything.

 

Wonder if this is the kind of fit that does fine until 6 months later. Any ideas?

 

Did thermal expansion tests with test tiles for these glazes, and they all came out fine - albeit with 3 layers of glaze on the edges though.

 

Thanks.

Pat

 

Clay body

OM4 - 22

Gladart - 22

Redart - 11

Hawthoren 40m - 43

Grog - 3

 

Glaze 1

Custer - 61

EPK - 20

Whiting - 18

 

Glaze 2

Custer - 21

EPK - 5

Whiting - 11

Silica - 40

Iron Oxide - 15

Unwashed Ash - 8

 

Share this post


Link to post
Share on other sites

 

Clay body

OM4 - 22

Gladart - 22   ( is this goldart?)

Redart - 11

Hawthoren 40m - 43

Grog - 3

The only addition supplying flux to this clay body is redart: and that is less than half the total minimum fluxes required for a cone ten body. Nearly 50% of the recipe is larger particle fire clays. Have you even done an absorption test on this body? I would estimate by the recipe it is approaching 8-10% absorption range? There is not enough iron present to make up for the lack of flux. this strikes me as an old Raku / wood fire recipe.  Do not think your glaze is the problem. Have you looked at the glaze shivers closely? Are there course particles present on the back of the shards?

 

Nerd

Share this post


Link to post
Share on other sites

Glazes don't look like low expansion ones, wondering if this is shelling and not shivering. Nerd, you don't think the Hawthorne is supplying enough extra flux? Looks like a somewhat similar V.Cushing recipe which has 10 Kona added to it. Patrick, how are you doing your shivering tests? 

Share this post


Link to post
Share on other sites

Min:

 

I ran his formula on Glazemaster (Clay Body) mode-- 1.64% alkali molarity. about half the required minimum. Hawthorne has 1.50% total alkali molar. The mine recently updated analysis sheets: Tony has not updated Insight yet: slightly higher than the old specs.

 

Nerd

Share this post


Link to post
Share on other sites

Min:

 

I ran his formula on Glazemaster (Clay Body) mode-- 1.64% alkali molarity. about half the required minimum. Hawthorne has 1.50% total alkali molar. The mine recently updated analysis sheets: Tony has not updated Insight yet: slightly higher than the old specs.

 

Nerd

 

Okay, enough said. 

Share this post


Link to post
Share on other sites

How thick are the rims of the bowls and cups that are shivering?  Also how sharp are the 'corners' between the wall surface and the rim surface?  I often see work that has problems due to not enough surface area to hold on to the glaze layer. The actual failure is in the clay body, not in the glaze. 

 

A thick layer of strong glaze can often cover up a structural design issue.

 

LT

Share this post


Link to post
Share on other sites

Thanks for the informed replies. I LOVE this forum for that reason. You guys/galls are great.

 

Nerd:

(1) re: absorption: A fired 44g shrinkage bar weighed 45g after a 24 hour soak at room temp. Shrinkage was just shy of 12%

Confession: Spent much more time investigating what makes a glaze tick and took body recipe on faith. ... Oops. Thanks for helping see what is becoming glaringly obvious.

(2) Shiver appearance. They are extremely thin and relatively smooth. No obvious course particles.

(3) Yep. Goldart - not Gladart (sounds like a inverse pun right about now)

 

Question: Can you put me on the information trail of understanding the significance of clay body alkali molarity, et.al. Again, did some glaze homework, so I'm familiar with certain concepts, but obviously have clay body homework to do.  Thanks.

 

Min:

(1) Wasn't purposing to to shiver test.  These were on a cup and a bowl - quarantined the entire lot until I can figure out what is going on. Thought I'd nailed it with test tiles - had a few glazes that crazed and a few that didn't. Made slight adjustments and ran with it.  The application difference was in glaze thickness on the pot.  On the pots that shivered, none of the shivers happened where glazes overlapped, and that got me thinking along the line of glaze problems.  Again, I'm seeing that the body might be screaming "Hello, McFly!"

 

LT:

I've got pics on camera. Let me get them off, crop, and post them, and you can see what I'm talking about. The rims aren't really too thin IMHO.

 

Thanks ya'll.

Share this post


Link to post
Share on other sites

Hi Patrick:

 

I see a failure to bond at what is known as the clay/glaze interface. The flux at the surface of the clay, and the flux in the glaze both adhere and bond to each other: creating a mechanical structure.. See below>>

 

Clayglaze interface

 

You can see the clay body (white) being pulled up into the glaze, and the glaze (blue) being pulled into the clay: a true mechanical bond. The lack of flux in the clay is causing the bond failure in this case.

 

 

Clay body                                                             Clay Body

OM4 - 22                                                               OM4   22

Glodart - 22                                                          GoldArt 22

Redart - 11                                                           RedArt  15

Hawthoren 40m - 43                                          Hawthorne 27

Grog - 3                                                                Grog  3

                                                                              Custer  11

Nerd

Share this post


Link to post
Share on other sites

Something wonky going on with the absorption test, 2.27% doesn’t mesh with what one would expect if the body is low on flux as Nerd pointed out. Try taking take a pot and put a drop of ink or food dye on the unglazed bottom of it and leave it sit for an hour or so then run it under the tap to wash the ink off. See how much the ink/dye stains the clay.

 

If you had crazing test glazes you are not going to have shivering with the same glazes; high expansion to craze, low to shiver. 

 

 There is a good article on testing clay bodies, before going into production,  ;) , here

Share this post


Link to post
Share on other sites

Something wonky going on with the absorption test, 2.27% doesn’t mesh with what one would expect if the body is low on flux as Nerd pointed out. Try taking take a pot and put a drop of ink or food dye on the unglazed bottom of it and leave it sit for an hour or so then run it under the tap to wash the ink off. See how much the ink/dye stains the clay.

 

If you had crazing test glazes you are not going to have shivering with the same glazes; high expansion to craze, low to shiver. 

 

 There is a good article on testing clay bodies, before going into production,  ;) , here

 

Quick update: soaked room temp test bar again for 24 hours (did NOT heat it first to drive off ambient, indoor moisture). Pre = 44g and post = 46g. Crazy huh? Regarding crazed glazes, those were the ones I chose not to use.  Ran with the ones that did not craze or only slightly crazed.  Narrowed my repertoire down to 4 glazes: 1 opaque whitish base, 1 transparent, and 2 tenmokus.

 

After chewing on the testing that I am going to do to tackle this problem (thanks again for helping see it), I have just about decided to drop down and play in the neighborhood of cone 6 for a while. But Nerd, I appreciate your adjustments to the cone 10 recipe I was using.  I will try it out, as I don't see myself abandoning the cone 10 world.

Share this post


Link to post
Share on other sites

Is the glaze actually falling off the fired pots?

 

It looks more like crawling to me.

Just very thin shards off of the rims as seen in the photos above.  I thought crawling was more of a body/glaze non-adhesion, coagulation kind of thing - kind of like water on a Rain-X windshield.

Share this post


Link to post
Share on other sites

 

        Clay Body                                                     Cone 10                                   Cone 6

OM4 - 22                                                               OM4   22                                 OM4      22

Glodart - 22                                                          GoldArt 22                             Goldart  22

Redart - 11                                                           RedArt  15                             Redart    15

Hawthoren 40m - 43                                          Hawthorne 27                     Hawthorne 23

Grog - 3                                                                Grog  3                                  Grog          3

                                                                              Custer  11                            Custer      15

Nerd

Share this post


Link to post
Share on other sites

 

 

        Clay Body                                                     Cone 10                                   Cone 6

OM4 - 22                                                               OM4   22                                 OM4      22

Glodart - 22                                                          GoldArt 22                             Goldart  22

Redart - 11                                                           RedArt  15                             Redart    15

Hawthoren 40m - 43                                          Hawthorne 27                     Hawthorne 23

Grog - 3                                                                Grog  3                                  Grog          3

                                                                              Custer  11                            Custer      15

Nerd

 

God, I love this place!  - Thanks.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

By using this site, you agree to our Terms of Use.