[Clayart] Blue haze on kiln shelves mystery

[Kathi Koester]

Hi Lisa,
I notice that ring on shelves occassionally too. I also leave bare clay
design areas ON my pottery and see it there too; the ‘haze’ is like a
toasty, shiny effect. I use a high iron clay.
Additionally, even my 5x20 base gives a toasty edge ‘haze’ to my clay
design. I appreciate that some unload kilns, seeing the faint ‘ring’ haze
and seek an answer. I just reload ;)
That curious, adventure, passion probabley also led us to the moon!
(whereas I never once wondered ‘how could i get to ‘that?’)
I will be curious to read the technical ‘outgassing’ explaination from our
pro’s on clayart.
Sincerely,
Kathi Koester
MN

On Mon, Oct 31, 2022 at 8:31 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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-- 
Sincerely,
Kathi Koester
612-867-0829
MAKNART Ceramics
https://maknartceramics.square.site/

Author: Our Piano Teacher ISBN: 978-1-64416-853-0
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