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Pres

Two Plates, Same Glazes? Different Shelves?

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I unloaded a glaze load today, with some nice things coming out. However, I got a strange, if not pleasant surprise. I have been using a liner glaze with zirconium/tin oxide opacifiers, a Cream Rust, Variegated Blue, with a spray of Rutile green overall. All but the first two are sprayed as the first two are dipped. The stain brushwork(iron oxide) show subtlety on both plates, but the one is purple.  Go figure. . . different shelves, yes, only thing I could think of that was different. However, on the same shelf as the purple one was another brown as the one pictured.

 

Can anyone figure out what I did differently, as I can't. They were all done the same day, all fired same load.

 

post-894-0-12265600-1503705107_thumb.jpgpost-894-0-25997200-1503705083_thumb.jpg 

 

 

 

 

best, 

Pres

GiselleNo5 likes this

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Pres,

 

Can I assume all cones on all shelves fell the same way?

 

My theory is cooling rate, which can affect iron colour. FeO has a tendency to reform into Fe3O4 if cooled slow enough. It's why Japanese black raku is quenched. My cone 4 black raku turns a plum brown if kiln cooled.

Edited by Tyler Miller

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Since the plates below were on a short 2" shelf level, and the shelf above was 6", I think your theory could be very correct. One of those things that happen that it takes a second head to figure out. I appreciate the response. Besides that I thought everyone would find it kind of .. . . cool, and in a way . . .it is.

 

best,

Pres

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I will say this and I am not sure if it is accurate to your glazes or if this is the cause. This is just a place to start with.

 

Whenever I mix small amounts of cobalt (.25g) with titanium(10g) glaze then spray a zircopax glossy glaze over. I get purple matting crystals. 

 

Just something to test if maybe you had more of the zircopax glaze on the other plate some how. Looking at the plate the one on the right seems to have a slightly hazier look, which is why I posted this. 

 

Anyways I could be way off, but this is what I have found in my experimentation with color in the 5 glazes I work with now.

Tyler Miller, glazenerd and Pres like this

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Babs,

No Mg anywhere. The stain has been very consistent over the years. I have used tin oxide in the past to promote pinks, and some purples, but have not had that happen much of late. Reason I use the mix of Zirconium and tin is for the softer look of the tin coloring, cutting the cost quite a bit. The Zirconium by itself was just too off white(cool gray) in color for me. This is the first time it happened, no big deal, but thought it an interesting puzzle.  

 

I like your thinking Joseph, as I do use cobalt in the Variegated blue, it is plausible. However, I do not spray the white over the others glazes, only spray the Variegated blue and the Rutile green. Neither of them contain Zirconium or tin.  Time for more testing I guess.

 

 

best,

Pres

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I think it's mostly a matter of glaze thickness and the proportions of each layer, and possibly temperature as well. A 2" shelf is going to heat a little differently than a 6" shelf. I don't think the cooling rate would be different enough between the two to cause any difference, though.

Tyler Miller likes this

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One of the reasons I posted it, It would be neat to be able to control it. Either coloring works well with the Rutile green, but the purple is a little more interesting.

 

 

best,

Pres

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I am not sure then. I was just giving my experiences with purple randomly showing up in some of my work. I do know that anything with titanium and cobalt sometimes can go to purple. The second plate picture looks like it has more microcrystals. SO maybe it did cool slower and had a thicker application of the rutile. 

 

Either way I think they both look very nice. 

 

EDIT: are both the pictures the center of the plate with the swirl? Because in the first picture you can see the swirl very obvious, but the second picture I can't tell if that is the same swirl or not, which means the glazes probably are thicker there on that second plate?

Edited by Joseph F

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One plate has a swirl, the other does not. I spray on the Variegated blue at an angle to try to catch texture on the object, then the Rutile green is sprayed perpendicular. It is puzzling to me, so I will see what happens in the next loads. Also will be working with a white stoneware, and want to see what happens there.

 

best,

Pres

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I have a glaze (it's commercial of course since that's all I use) that is a lovely smoky purple with a light float ... unless it's put on the top shelf. In which case it's a dark wine purple/burgundy color. 

 

I have another glaze that is an absolutely drop dead beautiful shade of blue unless it's put on the top shelf, in which case it turns this really ugly weird shade of blue that is similar and yet totally different. 

This process and all its' little quirks and details never ever ceases to fascinate me. 

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