[Clayart] Blue haze on kiln shelves mystery

Dragonbelly Ceramics lisa at dragonbellyceramics.com
Mon Nov 7 23:51:18 UTC 2022


Thank you very much, David and Roy. I have both of those frits available
and will test with the substitution. I very much appreciate the amazing
collection of knowledge here on this list.

Best,
LJ

On Mon, Nov 7, 2022 at 3:52 PM David Woof <woofpots at hotmail.com> wrote:

> 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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> >> >
> >>
> https://lists.clayartworld.com/pipermail/clayart/attachments/20221031/dd206c44/attachment.jpeg
> >> > >
> >> > >
> >> > --
> >> > 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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-- 
        http://www.dragonbellyceramics.com
*           where imagination meets function*
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