Lili Krakowski on fri 22 feb 08
Dear Anne de St. Sauveur!
I recently learned from a friend that Bentonite is better added in from the
start.
And so I recalculated (Glaze Master TM) your recipe and found that your
Alumina
is .484, and your Silica 3.612.
Which raises an eyebrow. That is a lot.
I do not know what FB means so that is not a clue, but you want a mottled
blue, I guess.
Here is what I would do.
1. [Try the glaze on another clay body] I put this in [] because while it
IS something that teaches one a lot--how different bodies interact with
glazes--as you have a clay body you have been using, you are not going to
give up on it for just one glaze.
2. Make a blend starting with your clay at 4 at one end and 17 at the other.
See what happens.
3. Replace the kaolin with ball clay. That will lower the alumina though
not sensationally, and may help with the melt.
My guess is that the awful color you got from the soak was that your glaze
requires a quicker cooling; that in fact the soak did nothing for the
pinholes, but ruined the color. I remember from childhood a game similar to
musical chairs. Someone sang or counted or whatever, and when the music
stopped, the players stayed fixed in their poses. Did your mother not tell
you when you were making faces that if the church bell rang while you were
doing that, your face would freeze in that grimace? Well the same thing
happens to glazes when the heat goes off. They become "frozen" (i.e. they
solidify) in their last constellation. Soaking often helps--but your glaze
obviously is not happy with that!
A question: Does the glaze go on the pot well? You do not say how it is
applied, but application can produce pinholes. A fairly stiff glaze, as
this one seems to be, can retain pinholes that came with the glazing.
Possibly having your bisque damp when glazing will help. Also check your
glaze application thickness. Not all glazes are happy with identical
application. (Test on a quite damp test tile. Also dip your test tile
once, the dip it in 2/3 of the way, then 1/3--and get three application
thicknesses.
Pinholes are a real nuisance. The pinhole theory is that gases have been
escaping but the holes they left in their passage have not had a chance to
heal. So one can try a higher bisque--this on the theory that there is
stuff left in the body that needs to burn out, and higher bisque would burn
off some of that earlier--or one can extend the firing at the top...I do not
know how that is
done with digital kilns but were I doing it on my [regular] kilns I would
turn two of the three switches from medium to high
and an hour later turn the third on high, rather than turning all three to
high at once. Or, see above, one can lower the melting point of the glaze.
Bonne chance
Lili Krakowski
Be of good courage
John Rodgers on fri 22 feb 08
Lili,
The FB plus description of the problems you describe make this sound
just like Chappell's Floating Blue. I use this glaze a LOT, and it
exhibits all the tendencies described. I use it almost exclusively on C5
B-mix, fire to cone 5 or 5 bent horizontal, and a fairly rapid cool.
This method gives me no running, nice mottling and almost - note I said
almost - no pinholes. I fire up pretty fast with the last hour +30 being
very slow. Then allow to cool normally. I fire with the bottm plug out.
Seems to help, thought I really don't know why.
Absolutely do not fire this glaze to cone six and above. You get snot
green, runs and pinholes.
Of all my glazes, this one - Floating Blue - is my favorite. It is
twitchy, and has to be mixed just so - as in distilled water only,
ingredients weighed out exactly, etc.. When done and fired right,
especially over a white clay, you get nice mottling, with brown
highlights and brown over edges. Very nice look. This is not an intense
blue like Cobalt blue, but a soft mottled blue with glossy surface. The
blue with brown highlights is very restful to look at. I sell more
pieces in this color than any other in my entire line.
Regards,
John Rodgers
Chelsea, AL
Lili Krakowski wrote:
> Dear Anne de St. Sauveur!
>
> I recently learned from a friend that Bentonite is better added in
> from the
> start.
> And so I recalculated (Glaze Master TM) your recipe and found that your
> Alumina
> is .484, and your Silica 3.612.
>
> Which raises an eyebrow. That is a lot.
>
> I do not know what FB means so that is not a clue, but you want a mottled
> blue, I guess.
>
> Here is what I would do.
>
> 1. [Try the glaze on another clay body] I put this in [] because
> while it
> IS something that teaches one a lot--how different bodies interact with
> glazes--as you have a clay body you have been using, you are not going to
> give up on it for just one glaze.
>
> 2. Make a blend starting with your clay at 4 at one end and 17 at the
> other.
> See what happens.
>
> 3. Replace the kaolin with ball clay. That will lower the alumina though
> not sensationally, and may help with the melt.
>
> My guess is that the awful color you got from the soak was that your
> glaze
> requires a quicker cooling; that in fact the soak did nothing for the
> pinholes, but ruined the color. I remember from childhood a game
> similar to
> musical chairs. Someone sang or counted or whatever, and when the music
> stopped, the players stayed fixed in their poses. Did your mother not
> tell
> you when you were making faces that if the church bell rang while you
> were
> doing that, your face would freeze in that grimace? Well the same thing
> happens to glazes when the heat goes off. They become "frozen" (i.e.
> they
> solidify) in their last constellation. Soaking often helps--but your
> glaze
> obviously is not happy with that!
>
> A question: Does the glaze go on the pot well? You do not say how it is
> applied, but application can produce pinholes. A fairly stiff glaze, as
> this one seems to be, can retain pinholes that came with the glazing.
> Possibly having your bisque damp when glazing will help. Also check your
> glaze application thickness. Not all glazes are happy with identical
> application. (Test on a quite damp test tile. Also dip your test tile
> once, the dip it in 2/3 of the way, then 1/3--and get three application
> thicknesses.
>
> Pinholes are a real nuisance. The pinhole theory is that gases have been
> escaping but the holes they left in their passage have not had a
> chance to
> heal. So one can try a higher bisque--this on the theory that there is
> stuff left in the body that needs to burn out, and higher bisque would
> burn
> off some of that earlier--or one can extend the firing at the top...I
> do not
> know how that is
> done with digital kilns but were I doing it on my [regular] kilns I would
> turn two of the three switches from medium to high
> and an hour later turn the third on high, rather than turning all
> three to
> high at once. Or, see above, one can lower the melting point of the
> glaze.
>
> Bonne chance
>
>
>
>
> Lili Krakowski
>
> Be of good courage
>
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>
>
John Sankey on sat 23 feb 08
"I recalculated (Glaze Master TM) your recipe and found that your
Alumina is .484, and your Silica 3.612. Which raises an eyebrow.
That is a lot."
Using Hesselberth&Roy's definition of Seger ratios (they exclude
boron and everything they consider to be a "colorant"), the
average RO2 (silica) of successful cone 6 gloss glazes in the
glaze database is 2.62 and of R2O3 (alumina) 0.31
(see http://sankey.ws/glazeanalysis.html for details)
H&R's finding that RO2 should be 3.5 and R2O3 0.4 (again, using
their definition of Seger) is clearly not adhered to by
clayarters. We prefer our glazes much more fluid and/or colorful.
John Sankey
--
Include 'Byrd' in the subject line of your reply
to get through my spam filter.
John Hesselberth on sat 23 feb 08
On Feb 23, 2008, at 9:28 AM, John Sankey wrote:
> H&R's finding that RO2 should be 3.5 and R2O3 0.4 (again, using
> their definition of Seger) is clearly not adhered to by
> clayarters. We prefer our glazes much more fluid and/or colorful.
John, where did we say this? Our 4 "rules" for stable glazes include
silica being greater than 2.5, preferably greater than 3 and alumina
greater than 0.25 and not greater than 0.45 at cone 6.
You also have to have an active enough fluxing system to throughly
melt the glaze (though, not in the book I have since settled on about
0.25 [+ or minus a bit] zinc or boron at cone 6) and not overload it
with colorants.
If you can tell me where we said the above I will try to correct it
because it is certainly not accurate.
Regards,
John
John Hesselberth
www.frogpondpottery.com
"Man is a tool-using animal....without tools he is nothing, with
tools he is all" .... Thomas Carlyle
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