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PatIsGone

"fitting" Glaze Shivers When Applied Thin?

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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

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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? 

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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

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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. 

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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

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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

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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

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        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

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