gjudson on tue 17 may 05
[GJJ] Marianne wrote:
Regarding glazes. This past spring I took a class from
William Tersteeg here in NE PA, someone who is highly
knowledgeable regarding glazes. However: we were only
able to touch the tip of the iceberg, with so many
other things competing for time.
I am going to look up some of the simple (simplified,
that is) lists he gave us regarding the function of
various standard ingredients. It was, for me, a good
start. Perhaps you know all this. Doesn't hurt. I'll
send it to you as soon as I can.
[GJJ] I have not had any personal help--till now with you and Steve--and
have just been working with books. I started off with Cuff's "Ceramic
Technology for Potters and Sculptors" but it was way over my head. I =
did
not have the discipline to work through it nor the background to support =
it.
As I mentioned I took both "Mastering Cone 6 Glazes" and "Cone 6 Glazes" =
as
recipe books and realize now that I need the instruction they offer more
than the recipes! I am aware of digital fire web site and have referred =
to
it frequently. I have been taking classes at Southwest School of Art =
and
Craft--which I have greatly enjoyed. But there we USE glazes--not make =
or
study or try to understand them. So I have taken up glaze making on my =
own.
I have not had great success yet--though no disasters either--but so =
much of
the trouble seemed related to the kiln problems that I am not =
discouraged.
Really I am very inspired to get a couple good glazes under my belt. I =
got a
copy of Ian Currie's "Smashing Glazes" today and intend to take a =
workshop
with him in September. It seems that he really narrows the focus down =
to
bite size in his book. =20
The helps that Steve Slatin has offered you and me in this dialogue make =
me
much more confident. The long post he gives today is a very rich =
overview
of just what I need to have at my fingertips as I wade into my glaze =
mixing
the next couple of days. Hope I can apply some of what he has offered =
to
good effect. =20
I am grateful for anything you have to share. Maybe together we'll =
break
through this challenge.=20
Gay Judson, San Antonio, TX=20
marianne kuiper milks on tue 17 may 05
Hello Gay,
Your first email was wonderful as is this last one.
I, too, have started this at "retirment' from musc at
age 57, after 43 years of teaching/performing with
great love. But now it's MY time, with 4 kids who
landed nicely.
Regarding glazes. This past spring I took a class from
William Tersteeg here in NE PA, someone who is highly
knowledgeable regarding glazes. However: we were only
able to touch the tip of the iceberg, with so many
other things competing for time.
I am going to look up some of the simple (simplified,
that is) lists he gave us regarding the function of
various standard ingredients. It was, for me, a good
start. Perhaps you know all this. Doesn't hurt. I'll
send it to you as soon as I can.
Unfortunately, when "glazes" are taught in classes, it
is usually limited to masks, scales, recalculating,
where stuff is, how to clean up. Then you have a nice
glaze and learned very little. For a level 1 or 2
college class this may make some sense, but it wasn't
satisfying to me.
Bill is coming over for dinner Saturday....... (got
questions? serve food) But also because we became
friends.
When browsing yesterday I hit upon a site that may
give you some satisfaction as well: ...sorry: it's on
our other labtop. Will send it separately.
Marianne
--- gjudson wrote:
> Steve and Marianne,
> I am following this conversation closely as I am in
> very much the same spot
> as Marianne. Steve's analysis and recommendations
> are just what I need
> right now, too.
>
> So the question that comes to mind, for me just now,
> is about using the
> GlazeMaster program to spot these adjustments. I am
> about to substitute EPK
> for China clay. If I compare the analysis of the
> two recipes--the original
> and the one in which I exchanged the EPK for China
> clay--what do I look for?
>
> And will I ever learn enough about these materials
> to know off the cuff what
> they do in the glaze? I working on it--but starting
> all this after
> retirement may be asking more of a declining memory
> system than it can
> handle.
>
> Thanks for all the good helps, all! Gay Judson, San
> Antonio, TX
>
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On
> Behalf Of Steve Slatin
> Sent: Monday, May 16, 2005 10:39 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Frits to Steve:
>
> 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
>
=== message truncated ===
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