[Clayart] Blue haze on kiln shelves mystery

David Woof woofpots at hotmail.com
Mon Nov 7 20:52:48 UTC 2022 

Hi Lisa,
Ron Said: "I just put your glaze through the Insight glaze calculator. It has just enough silica to be stable but over loading with oxides (especially copper) will probably result in some instability under acetic conditions. The expansion is a little high so it will craze over some bodies. Adding silica will help cure both problems."

Lisa, I had been debating sending a post suggesting substituting the Gillespie with Frit 3134, and Ron stated simple and clear advice as why this would be to your far-reaching advantage.

The 3134 as a substitute for the Gillespie would supply your glaze with the needed Boron and with extra Silica that would benefit your glaze as Ron reasoned.

I sub out Gerstley or Gillespie borate with frit 3134.   (Or in some circumstances 3124.)
To supply the Boron, Frit 3134 can be direct substituted 1-1 up to 15% in many glaze formulations.
Upwards of this level and higher you may need to adjust the percentage of Silica in the glaze recipe. (Then again, maybe not.)
Use the glaze calc. program, or do the pen and paper math.

Misneach,
David Woof..........................................................................................................................................
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
________________________________
From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of ronroy at ca.inter.net <ronroy at ca.inter.net>
Sent: Monday, November 7, 2022 9:08 AM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>; John Mcclure <mcclujo at gmail.com>
Subject: Re: [Clayart] Blue haze on kiln shelves mystery

Hi Lisa,

I just put your glaze through the Insight glaze calculator. It has
just enough silica to be stable but over loading with oxides
(especially copper) will probably result in some instability under
acetic conditions. The expansion is a little high so it will craze
over some bodies. Adding silica will help cure both problems.

Perhaps the spitting is the result of the zinc being reduced. Do you
have a vent running?

During bisque firing carbon may be left in the kiln bricks if there is
not enough oxygen present to burn it off. Zinc oxide is VERY sensitive
to any reduction and can reduce to the pure metal which in turn
volatilizes above 800C. If that is happening it could explain your
problem.

If you do not have a vent running or it is not working properly you
need to find a way to introduce more oxygen during your bisque
firings. Leaving the bottom and top spy holes at least partially open
during your bisque firing may do the trick. Keep in mind that some
clays have more carbon than others.

To test a vent to see if is working properly hold an open flame at the
air inlet - on my vent it's the top spy hole. If the flame is just
barely drawn in the vent is work properly.

Feel free to contact me if you think I can help further.

RR


Quoting John Mcclure <mcclujo at gmail.com>:

> 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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>> >
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>> > >
>> > >
>> > --
>> > www.pine-ridge.ca<http://www.pine-ridge.ca>
>> > Garden Blog: www.garden-on-the-ridge.blogspot.ca<http://www.garden-on-the-ridge.blogspot.ca>
>> > Pottery Blog: www.studio-on-the-ridge.blogspot.ca<http://www.studio-on-the-ridge.blogspot.ca>
>> >
>> >
>>
>> --
>>         http://www.dragonbellyceramics.com
>> *           where imagination meets function*
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Ron Roy
ronroy at ca.inter.net
Web page ronroy.net


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