[Clayart] Blue haze on kiln shelves mystery

[John Mcclure]

It appears to me that your test tiles are square tubes with much more
marking on the inside of the test tile. Also the marking appears to be more
of fine spots verses a haze, where I think of a haze looking more like a
watercolor or airbrush would make if they were used. So I go with glaze
spitting. If this is true the venting may not be a cure.
John McClure

On Tue, Nov 1, 2022 at 9:55 PM Dragonbelly Ceramics <
lisa at dragonbellyceramics.com> wrote:

> Dear Kathi, William, Hank, Wayne, and Lis,
>
> Thank you so much for your answers and suggestions! The kiln manager
> notified me that when they had done some maintenance on the kiln, the vent
> had been reattached incorrectly, so I'm thinking that the fumes weren't
> getting vented properly, hence the haze.
>
> I'll report back after the next kiln!
>
> Best,
> LJ
>
> On Tue, Nov 1, 2022 at 4:12 PM Lis <lis.allison at primus.ca> wrote:
>
> > Cobalt, copper and chrome all volatilize in the firing and the vapours
> > will land on the kiln shelves. Saggars would contain the vapours.
> >
> > Lis
> >
> > On 2022-11-01 12:11 p.m., W Seidl wrote:
> > > Perhaps a stupid question...  Have you tried firing those tiles in a
> > > saggar?  That might eliminate/mitigate any environmental issues going
> > > on in the kiln during firing.  Still happening(?), then look to the
> > > glaze. The "sealed" environment inside a saggar, blah blah...
> > >
> > > Just a thought. Might not be a cure, but might get you closer to the
> > > cause.
> > >
> > > Best,
> > >
> > > Wayne in Maine
> > >
> > >
> > >
> > >>> On Oct 31, 2022, at 1:26 PM, Dragonbelly Ceramics
> > >>> <lisa at dragonbellyceramics.com> wrote:
> > >>>
> > >>> Hello, fellow clay folk -
> > >>>
> > >>> I'm the glaze tech at a community studio in Ware, MA and have a
> > >>> mystery to solve. I've been working on variations of a base glaze to
> > >>> get a blue we like for the studio. I chose our studio white as a base
> > >>> (omitting the opacifier) because it's the most stable/happy glaze we
> > >>> have.
> > >>>
> > >>> Over the course of the past 2 months, I've been testing various
> > >>> combinations of copper carb, cobalt carb, rutile, & RIO. I found a
> > >>> blue the studio all liked and did one additional test. While the test
> > >>> tiles look as I had expected, they left a blue haze on the kiln shelf
> > >>> in the shape of the square tile base. (See attached photos of kiln
> > >>> shelf and test tile).
> > >>>
> > >>> Cone 6, oxidation, electric Skutt kiln, fired using preprogrammed
> slow
> > >>> glaze. Cones verified the firing at cone 5-6 (depending on the
> shelf).
> > >>>
> > >>> White Base:
> > >>>
> > >>> minispar 200    46.1
> > >>> Silica                 19.7
> > >>> Gillespie Borate 13.5
> > >>> Whiting               8.2
> > >>> Dolomite             5.9
> > >>> Zinc Oxide           3.9
> > >>> Bentonite             2
> > >>>
> > >>>
> > >>> Problematic color tests:
> > >>>
> > >>> WB-10:
> > >>> +cobalt carb 2
> > >>> +copper carb 2
> > >>> +rutile            1.5
> > >>>
> > >>> WB-13
> > >>> same as WB-10, +zircopax 7
> > >>>
> > >>>
> > >>> Variables I've already accounted for:
> > >>> 1. clay body
> > >>> I've used the same batch of test tiles, made months ago with bmix
> > >>> and laguna 90
> > >>>
> > >>> 2. White base chemistry - at the start of this process, I mixed a
> > >>> large batch of the base and have been using small batches of it to
> > >>> create colors to test. The initial tests (using similar oxides in
> > >>> slightly different concentrations) did not cause any problems.
> > >>>
> > >>> 3. Specific gravity of the tests
> > >>> All measured at or close to 1.38, using a digital scale and a 10-0 ml
> > >>> graduated cylinder.
> > >>>
> > >>> 4. application on the test tiles: all tiles dipped to a count of 3 by
> > >>> one person (me)
> > >>>
> > >>> 5. Kiln placement - same haze was seen with tiles places on multiple
> > >>> shelves.
> > >>>
> > >>> Does anyone have any idea what's causing the blue haze??
> > >>>
> > >>> Best,
> > >>> Lisa Janice Cohen
> > >>>
> > >>> (Attached photos of one of the test tiles and of the shelf)
> > >>> --
> > >>>         http://www.dragonbellyceramics.com
> > >>>            where imagination meets function
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> > >
> > --
> > www.pine-ridge.ca
> > Garden Blog: www.garden-on-the-ridge.blogspot.ca
> > Pottery Blog: www.studio-on-the-ridge.blogspot.ca
> >
> >
>
> --
>         http://www.dragonbellyceramics.com
> *           where imagination meets function*
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