[Clayart] Blue haze on kiln shelves (The Back Story)

Fri Nov 11 03:00:34 UTC 2022

Thank you so much for this, John. I'm just learning how to use glazy to
recalculate glazes. This is very helpful.

Best,
LJ

On Thu, Nov 10, 2022 at 10:15 AM John Post <johnpost89a at gmail.com> wrote:

> Here are links to two recalculations of the White Base glaze that is having
> the spitting issues.
>
> The first revision is an exact match of the original glaze but swaps out
> the Gillespie for Frit 3134 and EPK.
> 1st revision link
> https://glazy.org/recipes/279862
>
> The second revision has 10% EPK which is a slight increase. I did this to
> help it behave well as a slurry.
> It also has some added silica to keep the alumina to silica ratio the same
> as the original.
> https://glazy.org/recipes/279863
>
> Original recipe link
> https://glazy.org/recipes/278970
>
> John Post
>
> On Thu, Nov 10, 2022 at 6:06 AM Dragonbelly Ceramics <
> lisa at dragonbellyceramics.com> wrote:
>
> > Thank you, David. As always, really excellent information. I am grateful.
> > Our bmix is the cone 5. All our clays are cone 5 or 6 stoneware. I do
> > suspect our kiln is not firing as well as it could be. It's been run hard
> > for quite some time now. We finally have a second kiln and can take this
> > one off line to be looked at and parts replaced as needed.
> >
> > While there are many joys in being part of a community studio, one of the
> > frustrations is the process of requisitioning supplies can be needlessly
> > complicated. We ran out of cone packs. When we finally received a new
> > supply, the 5's and 7s were fine. They gave us the wrong ones for the 6s.
> > So we're waiting. Currently firing with the 5 and 7 cones only.
> >
> > Best,
> > LJ Cohen
> >
> > On Wed, Nov 9, 2022 at 6:38 PM David Woof <woofpots at hotmail.com> wrote:
> >
> > > Hi Lisa,
> > > the intrinsic behavior of Gerstley and Gillespie Borates that produce
> > > problems similar to your description are usually from two mechanisms:
> > > Immiscibility and Solubility.
> > >
> > > "Immiscible" describes a formulation of materials that are physically
> > > resisting, or incapable of mixing well and attaining a homogenized
> state
> > in
> > > the glaze slop..
> > >
> > > Which means that the solubility of several of the materials present in
> > the
> > > glaze slop are prone to migrate, carrying away oxides as well, and so
> > > become separately volatile, with propensity to off-gas, spit, or fume,
> > > which create the halo's you describe.
> > >
> > > This agrees with what Hank, Bill, Ron...et.al....previously posted
> > > regarding the migration of soluble constituents.
> > > Gillespie Borate was formulated to provide a standardized Borate
> product
> > > when the mine was running out of commercially mineable Gerstley Borate.
> > > The soul crunching reality (I'm no fan) was to now provide a
> > > "Synthetically" consistent formulation,  though still providing the
> > > intrinsic character Old Gerstley was known for, and revered by some
> > folks.
> > >
> > > Of number one concern is that while the solubility of these borates
> > > contributes to the esteemed variegated Gillespi glaze surfaces via
> > > migration of the soluble oxides, this effect becomes exaggerated when
> > mixed
> > > with other slightly soluble glaze materials and oxides.
> > >
> > > There are other simple ways to achieve similar variegated glaze effects
> > > and these provide virtually trouble-free substitutions.
> > > Others may wish to chime in here as there are no secrets.
> > > ************************************************************
> > > Another question to ask: is the B-Mix your community studio is using
> cone
> > > 5 or the cone 10 version?  If cone 10, then at cones 5/6 the body is
> not
> > > becoming sufficiently dense or vitrified at any time during the 5/6
> > firing
> > > to prevent soluble constituents from migrating thru the body of the
> tile.
> > > +++++++++++++++++++++
> > > Also, your use of the pre-programed firing schedule could be suspect
> > > because the cone choice setting will eventually read false because of
> the
> > > natural degradation of the thermocouples, causing "drift" from
> > representing
> > > the actual cone achievement needed for Body/Glaze maturation.
> > > Set cone pacs in the firing setting to witness what your preprogrammed
> > > "cone 6  setting" is actually doing.
> > >
> > > Best wishes,
> > > David
> > >
> >
> Woof.........................................................................................................................
> > >
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> >
> > --
> >         http://www.dragonbellyceramics.com
> > *           where imagination meets function*
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        http://www.dragonbellyceramics.com
*           where imagination meets function*
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