marianne kuiper milks on tue 17 may 05
Hi Steve,
"It is heart-warming to see that one can find friends
in corners where one was not looking."
But the plaster sounded great: I had a wonderful
belly-laugh.
The work you put in to answer my questions is
fantastic and highly appreciated!! I compared it to
explaining more intricate music theory to someone who
had played for a while, but never considered the
knowledge behind it. It's often hard to answer, put
things in logical order, when you're trying to play
catch-up with that person.
I've printed it off, along with the other suggestions
(and sympathy!) I received and, as with Bayleys, will
sit down on several occasions and slowly put it all
together. I hope.
And by the way: I have had good success in the past
with glazes, but they were mixes from Standard
Ceramics. I want to learn to do my own, and not
simply from a recipe but from learning why things
work.
I know for sure that you are right- the kiln is fine,
application should be ok and the cones fine as well.
So it's me.
We have a spring and I've even substituted the water
for bottled - just to compare - afraid that ours may
have conflicting substances. It's a good thing I have
Clayart friends and am, by nature, a curious and
tenacious person.
Thanks again (everyone) and I will report back when I
have hit a good firing.
Marianne
--- Steve Slatin wrote:
> Marianne --
>
> OK, let's start at the bottom and work backwards.
> It's not any language I speak, or French or Latin or
> even German, lemme see ... might be Dutch, but I
> don't
> speak any Dutch, still, to take a crack at it --
>
> "Het is hart-verwarmend dat men vrienden vindt in
> plaatsen waar we niet zoeken"
>
> It is heart warming that my friends arrive in
> plaster
> with no socks? Either I'm wrong or that's one of
> those folk-sayings that just doesn't translate.
> (I'm
> a language dummy who spent 20 years living mostly in
> other countries and the last 10 in a multi-lingual
> household, so I'm used to being wrong. And to
> things
> not translating.*)
>
> From your description I'd guess your glaze was
> 'immature' -- mixed so that it'd have taken more
> heat
> work than it got to fully vitrify.
>
> Bailey's GA12 is actually Tony Hansen's 5 x 20, a
> subject about which I have recently shown myself to
> be
> more than moderately ignorant (though I've used the
> glaze, and it's great). GA14 is a reformulation to
> use UK frits.
>
> Now, I'm not 100% clear on what you were mixing, but
> I'm presuming you used the percentages in GA14 with
> the spar and frit from GA14.
>
> If I am wrong and you used the 5 x 20 amounts and
> the
> spar and frit from GA14, that was likely your
> problem.
> The percentages in GA14 call for more borate-rich
> frit
> and less china clay. This is the direction to lean
> in
> to make a glaze shinier (if possibly a bit runnier).
>
>
> The issue with GA14 is that it's not a particularly
> exact reformulation of GA12 -- for example, GA14 has
> 20.16% total fluxes vs. 22.23 for 5 x 20, and only
> 3.95 boron vs. 4.47 (B2O3). (At cone 6 boron is
> largely melter. For higher temperatures, it's more
> often used as a glass former.) Also, it's got less
> alumina and a higher silica/alumina ratio. (This
> seems to be how Bailey makes it work with less
> flux.)
> With the percentages for GA12 and the materials
> specified for GA14, you get only 19% flux, 3.33
> percent boron, and more alumina. It no longer
> looks
> like a Cone 6 glaze.
>
> Then we get your individual substitutions from the
> GA14 recipe. EPK for china clay normally should be
> no
> problem. EPK is one of the many kaolins commonly
> used
> by potters. There are a few kaolins that are
> somewhat
> different (like Tile #6) but most potters will
> substitute grolleg, helmer, and EPK pretty freely.
> Look at the analyses on pps. 117-118 of Bailey,
> though
> -- his N50 China Clay and the EPK do differ in that
> EPK has more alumina and less silica.
>
> Next, we look at the feldspar substitution. G-200
> is
> a potash feldspar, and the analysis of Bailey's
> P-spar
> and G-200 are close. One difference is that G-200
> has
> about 1.5% more alumina ... see where we're going?
> Unfortunately, every step you took, albeit small,
> was
> away from the target you started with.
>
> Now on heat, it's not entirely clear if you got a
> good
> Cone 6 firing. How far over were the cone 6 cones?
> A
> 180 degree bend, with the tip of the cone almost
> touching the shelf is what I try to get. It's
> possible that you got a bend and the cone is
> pointing
> out horizontally, which is a fractional cone below
> your heat work target. Many glazes will work at
> this
> (cone 5 1/2 or 5 2/3 or whatever) but not all will.
>
> If your tips were practically touching (or touching
> the kiln shelf) then you were at that cone or above
> it. If that was the case, we're back to looking at
> the glaze and if you had enough melters.
>
> To put this ramble together --
>
> First, look at your cones. Did you make cone? If
> not, put those same cones back in (they've got the
> heat work in them that your work has) and refire
> until
> cone 6 is down. That might solve your problem.
>
> Next, if the cones are OK, check your ware. Are
> some
> sides of some pots pretty well vitrified, and others
> a
> mess? If so, it could have been heat distribution
> inside your kiln. For glaze firing you need a bit
> of
> space between pieces so the hot air can circulate.
> If
> the pots that were on the outside rim of your
> shelves
> fired properly on the side next to the elements.
> The
> solution is to load the kiln again with fewer pieces
> and adequate ventilation space, and refire.
>
> Now, if your cone 6 cones were all tip down to the
> shelf and your pots are uniformly unacceptable,
> you're
> pretty much secure in thinking the glaze is the
> problem. Take heart, you've got a known problem
> with
> an obvious solution -- you didn't melt, you need
> more
> melters, and to get there you need to add more of
> the
> ingredient -- the frit -- that bears the most
> melters.
>
>
> So how much frit do you add? That's a problem; but
> in
> my experience getting the frit within 2% of the
> target
> amount will generally give you some kind of a good
> glaze. My solution for you would be to add 2% of
> the
> total amount of your dry ingredients, test on a
> single
> tile or whatever, and, if it doesn't work, add
> another
> 2%. (Because the frits have other materials besides
> melters, you're adding much less than 2% melters
> with
> each experiment.) If you know how to do a line
> blend
> you could do that, and get several sample
> concentrations of additional frit tested at one
> time.
>
> Sorry it didn't work well for you. Best wishes --
> Steve Slatin
>
> I'm lazy, I'd just do it one whack at a time, and
> stop
> when the glaze began to mature.
>
>
>
> *(From all of this there's really only one thing I
> learned -- never ask an Iranian, Afghan, or Tajik
> cook
> if they know how to make cous-cous. Don't ask why,
> just trust me on this.)
>
> --- marianne kuiper milks
>
> wrote:
>
> > Dear Steve,
> >
> > I took an MB recipe GA12, which I then substituted
> > for GA14, all of which ingredients I have. Subst.
> P
> > Feldspar for G200 (which Bill Tersteeg, my
> > prof/friend said was fine, then I subst Kaolin/EPK
> > for China clay.
> > Made a small batch, made a triplicate sets of
> > testtiles and cross-color test tiles. Also used a
> > few useless pieces (chipped, etc, for samples: one
> > of home-made clay, one of Pitt 119 and one Pitt
> 213
> > (porcelain) --How am I doing so far? I felt VERY
> > scientific! I divided it all into 4 equal batches
> > and added samples (re-mathed) of the colorants
> > suggested on page 105, to end up with pale green,
>
=== message truncated ===
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