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BornonSunsetCeramics

Crawling matte glaze. Any hope of saving these?

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Hi All,

I'm having a heck of a time with these Duncan true 5 matte glazes. They keep crawling! I'm guessing the glaze pooled in the edges of these low serving bowls, and that's why they crawled...? Is there any hope is saving these? Also, that crack in the dish on the left is in the white underglaze... and happened during the bisque firing. There's no crack in the dish it's self, what could have caused this to happen?

 

Thanks so much everyone!

crawling plates.jpg

Edited by BornonSunsetCeramics

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I fired to cone 5 with a 15 minute hold on the medium program in my Skutt. All were bisque fired to cone 04 on slow. They each have white underglaze on the interior (Amaco VU) which was applied at the green stage before the bisque. I applied the duncan glaze to the middle of each and then  speedball clear just around the walls of the dishes prior to the glaze fire, since I was planning to use them as serving vessels. The clay is SBF cone 5/6 Aardvark. 

I placed witness cones and they read as follows: ^4: flat and broken, ^5: touching the kiln shelf, ^6: slight bend to about 1 o'lock position.

Thank you so much!

Edited by BornonSunsetCeramics

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Looks like the matte shrunk away towards the center of mass, I've had a similar problem when glazing only one surface.  The glaze was fine if I glazed the inside and outside, but would pull and sometimes warp a rim if I only put it on the inside.  Something about the inside shrinking at the same rate as the outside.  Probably not what happened here but it could be.  I don't think there's any saving those though, you could try refiring but don't count on it

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I was careful and brushed the clear on the sides, so if there is overlap its very minimal. 

I used a white underglaze because I was hoping for a very rich opaque, yet light color matte interiors to contrast the warm buff clay body. I was afraid not using an UG would muddy the color of the glazes. 

Any clue why the white UG would crack in a circle that way? I guess the glazes may not fit my clay body very well... which is a shame because it's a pretty buff color and throws so nicely! 

I'm so bummed. 

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I would be surprised if that crack does not go through the clay pot also , it Will eventually.

When applying under glaze to one surface of the pot it  pays to run a dampened brush over entire pot then apply the under glaze . Differences in moisture can cause cracking like this as  pot dries at different rates according to underglazed or not 

Would appears glaze may be too thick 

The crack on base. How thick is the base conpared to the walls?

Edited by Babs

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Matt glazes for liner glazes are not a good solution for functionality . Its not as easy to clean them as they are not as smooth.

It looks like your clear and the Matt to not work well where they touch.

I do not think there is any hope for them-just start over

I would use a liner glaze on the inner walls and bottom thats all one glaze and is not matt.

Matts can put tension on pots as well especially on the inside.

Edited by Mark C.

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@BornonSunsetCeramics, going forward I would really suggest making up some test tiles or even quick crude test pots to try your underglazes and glazes out on before trying them out on actual pots. Try all the combinations of underglazes beneath glazes, clear over the matte and vice versa. If they look okay after the glaze firing try rubbing a fork or spoon over the glazes and see if they cutlery mark and if crazing is something you want to avoid then test your test pots for that (with a stress test). 

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