Maria Elaine Lanza on tue 4 may 99
What can be done to this ^4-^6 oxidation glaze recipe posted by Chris
Campbell last year to stop it from running yet still maintain the color
intensity (true to its name "Noxzema Blue") and surface finish (glossy)?
decrease the gerstley borate? increase the EPK proportionately?
custer feldspar 38.1%
dolomite 10.0
EPK 9.6
silica 9.5
gerstley borate 9.0
zinc oxide 9.4
cobalt carbonate 3.5
Totals 89.6%
My glaze calc program adjusted the ingredient amounts to equal 100%
(below)... haven't tested this formula yet... would you guess that the
running would still be a glaze problem with this adjustment too? I
understand that testing is the best way to go, but I'm curious about the
logic of the program... any explanations?
custer feldspar 42.5%
dolomite 11.2
EPK 10.7
silica 10.6
gerstley borate 10.6
zinc oxide 10.5
cobalt carbonate 3.9
Total 100.0%
Appreciate any comments that you may have on correcting the running
problem... will test and report back. Thanks!
Marie Elaine
Barney Adams on wed 5 may 99
Hi,
My guess is the zinc is so high it is giving more flux action. Why not just
leave most of the values close to the norm and bump up the EPK. That should
get the alumina up to stiffen the glaze. You may even do a range of tests
that
will target in the best stiffness with out loosing the color/glossiness. Of
course
I defer to Ron, Tom and the other gurus.
I adjusted it in Insight trying for the right expansion value and got
Two Recipes: & Untitled Recipe 2
=================================
custer.............. 40.00 40.00% 38.10
44.51%
DOLOMITE............ 10.00 10.00% 10.00 11.68%
EPK KAOLIN.......... 13.00 13.00% 9.60 11.21%
SILICA.............. 19.00 19.00% 9.50
11.10%
GERSTLEY BORATE..... 9.00 9.00% 9.00 10.51%
ZINC OXIDE.......... 9.00 9.00% 9.40 10.98%
======== ========
100.00 85.60
CaO 0.27* 5.42% 0.26* 6.39%
MgO 0.18* 2.67% 0.18* 3.15%
K2O 0.13* 4.54% 0.13* 5.10%
Na2O 0.08* 1.82% 0.08* 2.07%
ZnO 0.34* 10.00% 0.35* 12.35%
Fe2O3 0.00 0.26% 0.00 0.26%
TIO2 0.00 0.04% 0.00 0.04%
B2O3 0.11 2.82% 0.11 3.33%
AL2O3 0.36 13.18% 0.31 13.47%
SiO2 2.72 59.23% 2.08 53.83%
P2O5 0.00 0.02% 0.00 0.02%
COST/KG 1.59 1.73
Si:Al 7.64 6.79
SiB:Al 7.95 7.16
EXPAN455.99 516.92
You probably have quite a bit of play with the silica/alumina ratio yet
to play with to adjust for what you want.
Barney
Maria Elaine Lanza wrote:
> ----------------------------Original message----------------------------
> What can be done to this ^4-^6 oxidation glaze recipe posted by Chris
> Campbell last year to stop it from running yet still maintain the color
> intensity (true to its name "Noxzema Blue") and surface finish (glossy)?
> decrease the gerstley borate? increase the EPK proportionately?
>
> custer feldspar 38.1%
> dolomite 10.0
> EPK 9.6
> silica 9.5
> gerstley borate 9.0
> zinc oxide 9.4
> cobalt carbonate 3.5
>
> Totals 89.6%
>
> My glaze calc program adjusted the ingredient amounts to equal 100%
> (below)... haven't tested this formula yet... would you guess that the
> running would still be a glaze problem with this adjustment too? I
> understand that testing is the best way to go, but I'm curious about the
> logic of the program... any explanations?
>
> custer feldspar 42.5%
> dolomite 11.2
> EPK 10.7
> silica 10.6
> gerstley borate 10.6
> zinc oxide 10.5
> cobalt carbonate 3.9
>
> Total 100.0%
>
> Appreciate any comments that you may have on correcting the running
> problem... will test and report back. Thanks!
>
> Marie Elaine
Chris Schafale on wed 5 may 99
Hi Marie Elaine,
I wasn't sure if you had actually tested this glaze or not, from
your post. I did try it, and didn't have a problem with running
-- in fact, mine didn't melt all that well. I've always wondered
if there was something left out of the recipe, since it adds to
89.6 instead of the usual 100. By the way, converting the recipe to
100 parts, as your program did, doesn't change the relative amounts
of the different ingredients at all, just converts them to
percentages of a total batch, which is the usual way of presenting
glaze recipes. Although, normally, the colorant (cobalt) would not
be included in the 100 parts, so this one would be expected to sum to
103.5 when the cobalt is included.
This glaze is low in silica, as I'm sure you saw from your
glaze calc program, and the alumina is on the low side as well
(though within limits), so an addition of EPK would make sense, would
make the glaze more durable, and would probably reduce running.
How about the following? (I added both EPK and silica, to keep the
Al:Si ratio similar to the original)
Noxzema Blue Plus
============
CUSTER FELDSPAR..... 38.10 36.81%
DOLOMITE............ 10.00 9.66%
EPK KAOLIN.......... 15.50 14.98%
SILICA.............. 17.50 16.91%
GERSTLEY BORATE..... 9.50 9.18%
ZINC OXIDE.......... 9.40 9.08%
+cobalt carbonate.... 3.50 3.38%
========
103.50
Good luck, and do post the results if you test this version.
Chris (Schafale, not Campbell, though we're both from Carolina, to
make things confusing)
> ----------------------------Original message----------------------------
> What can be done to this ^4-^6 oxidation glaze recipe posted by Chris
> Campbell last year to stop it from running yet still maintain the color
> intensity (true to its name "Noxzema Blue") and surface finish (glossy)?
> decrease the gerstley borate? increase the EPK proportionately?
>
> custer feldspar 38.1%
> dolomite 10.0
> EPK 9.6
> silica 9.5
> gerstley borate 9.0
> zinc oxide 9.4
> cobalt carbonate 3.5
>
> Totals 89.6%
>
> My glaze calc program adjusted the ingredient amounts to equal 100%
> (below)... haven't tested this formula yet... would you guess that the
> running would still be a glaze problem with this adjustment too? I
> understand that testing is the best way to go, but I'm curious about the
> logic of the program... any explanations?
>
> custer feldspar 42.5%
> dolomite 11.2
> EPK 10.7
> silica 10.6
> gerstley borate 10.6
> zinc oxide 10.5
> cobalt carbonate 3.9
>
> Total 100.0%
>
> Appreciate any comments that you may have on correcting the running
> problem... will test and report back. Thanks!
>
> Marie Elaine
>
>
Light One Candle Pottery
Fuquay-Varina, NC
candle@intrex.net
Paul Lewing on fri 7 may 99
Marie Elaine,
Adjusting the total of the amounts to 100 from 86 did nothing to the
relative proportions, so it will just produce a slightly larger sample
of the same glaze.
It's somewhat of a puzzle to me to know why this glaze would run. Have
you tested it more than once? Perhaps you made a mistake in weighing
out your ingredients.
The silica is low by molecular standards, but not particularly low when
considered on a percentage by weight basis. The alumina is also low,
but within most limit formulas, and the ratio of Si to Al, at 6.81, is
well below what I would expect to see in a runny glaze. Usually it's
glazes with a ratio over 15 or so that run. And the zinc is a bit high
according to limit formulas, but I'm currently using one with ZnO at
about .6 (yours is .35) and it doesn't run. In fact, I just completed a
series of tests in which I doubled the amount of zinc in my glaze, up to
about 25% of the batch, and it actually got kind of matt, not more
runny.
So..... The first thing I'd do is make the test again, if you've only
tried it once. If that is the same result, I'd try adding more EPK or
more silica, or both.
But as long as ZnO is such a dominant flux, you're going to get
Noxzema-bottle blue from cobalt, no matter what else you do.
Happy testing,
Paul Lewing, Seattle
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