Jackie Shaw on fri 16 nov 07
Hi All,
I am a novice at glaze mixing, but have mixed several successful glazes
from recipes (MC6G and others). I would like a CLEAR, buttery or satin
matte glaze, ^6, for use on stoneware.* (I've been sucked into the Clayart
Archives -- such a great resource for so many things -- for several hours
looking for such but no luck).
Can the base glaze of ANY recipe be used as a clear glaze? Or might some
of the basic ingredients--or combinations of them-- make it opaque? (This
question will probably verify my novice status!) I am considering using RR
& JH's "High Calcium Matte/Semimatte Base 1.
I am struggling to become familiar with all the glaze components and all
the variables inherent in creating and firing glazes, but I've a long way
to go, and probably not enough years left to get there.
Another question, can Custer Feldspar be substituted for G-200 Spar? I
notice in MC6G that the material analysis seems vey close for the two.
But I don't know how much variation is ok without causing problems. -- So
much to learn!
Clays I'm using: Highwater's Red Rock & Little Loafers; Campbells
Shenandoah Limestone; Standard's #s 153, 553, 181, 306.
Thanks so much for any help.
Jackie
John Hesselberth on fri 16 nov 07
Hi Jackie,
See below interspersed.
On Nov 16, 2007, at 3:22 PM, Jackie Shaw wrote:
> Can the base glaze of ANY recipe be used as a clear glaze? Or might
> some
> of the basic ingredients--or combinations of them-- make it
> opaque? (This
> question will probably verify my novice status!) I am considering
> using RR
> & JH's "High Calcium Matte/Semimatte Base 1.
Any base glaze can be used as a "clear" glaze, but notice I put clear
in quotes. Glossy base glazes generally are pretty clear if properly
formulated and well melted during firing. Matte glazes are almost
always a bit cloudy and sometimes a lot cloudy. The reason is that
what makes them matte are small crystals that precipitate out on
cooling and those crystals also hurt the clarity. In some respects a
"clear matte" is an oxymoron. However to get it as clear as possible
keep the thickness of the glaze coating as thin and uniform as you
can and still get good coverage.
>
> I am struggling to become familiar with all the glaze components
> and all
> the variables inherent in creating and firing glazes, but I've a
> long way
> to go, and probably not enough years left to get there.
Ah, but keep trying. You are asking questions that indicate a curious
mind--you'll be surprised how quickly you will learn.
>
> Another question, can Custer Feldspar be substituted for G-200 Spar? I
> notice in MC6G that the material analysis seems vey close for the two.
> But I don't know how much variation is ok without causing problems.
> -- So
> much to learn!
Usually these two feldspars can be substituted one for one if the
percentages in the glaze are fairly low. So what is fairly low?
Certainly less than 10%; maybe less than 20%. At 30 and 40% I would
test or learn how to adjust with the help of glaze calculation software.
Regards,
John
John Hesselberth
www.masteringglazes.com
www.frogpondpottery.com
John Sankey on sat 17 nov 07
"I would like a CLEAR, buttery or satin matte glaze, ^6, for use
on stoneware"
Jackie, your question is exactly what my database will shortly
allow Clayarters to ask. A proper interface is on the way, but in
the meantime I did a quick search:
A: Roy Clear 1
B: Ron Roy
C: 6
E: 25 feldspar,G-200
E: 20 borate,Gerstley
E: 20 silica
E: 15 dolomite
E: 15 kaolin,EPK
E: 5 Wollastonite
F: semigloss
H: Alisa Clausen: clear, semi gloss, stable glaze. No discernable
difference where double dipped.
A: Chappell Clear Semi Gloss
C: 6
E: 45.7 feldspar,F-4
E: 15.2 silica
E: 12.9 borate,Gerstley
E: 12.7 talc
E: 9 dolomite
E: 4.5 kaolin,EPK
E: 1 Bentonite
F: semigloss
H: Alisa Clausen: used Forshammer Feldspar for F-4. Clear semi
gloss. Lines of burgundy stain, RIO and cobalt oxide all came
well through the glaze, with stable edges. Has a satiny feel.
"Can the base glaze of ANY recipe be used as a clear glaze?"
No
I'm about 80% through entering the archived tested glazes...
--
Include 'Byrd' in the subject line of your reply
to get through my spam filter.
claystevslat on sat 17 nov 07
Jackie --
There are some glaze recipes that are really
sensitive, and even a substitution of similar
items requries recipe adjustments.
Recipes that are recommended for beginners often
accomodate slight deviations, and if you do a
substitution like Custer/G-200 you probably won't
notice the difference.
The reason why they can accommodate the substitution
is that they are formulations in the center of the
range of what 'works' for a particular type of firing.
You could get a good glaze with slightly more flux or
slightly less, slightly more silica or slightly less,
slightly more alumina or slightly less.
Custer and G-200 are quite close. The key differences
IMO, are --
Custer G-200
69.0 66.3 Silica
17.3 18.5 Alumina
13.2 13.8 K/Na
There are other differences, but in my experience
they're usually not so important.
Now that we've identified the greater differences,
we have to think of how important they may be.
What percent of the glaze recipe is made up of
your feldspar?
The silica difference looms large, but 3% of a
feldspar when the feldspar is, say, 10% of the
recipe works out to 0.3% of the glaze -- which
in most glazes will be a difference you will not
even be able to see. (Most ^6 glazes fall in
the range of 60-70% silica.)
The alumina difference, a seemingly less significant
1.2%, if we're dealing with 10% of the glaze, is
0.12%, a seemingly trivial amount, but which may
be more significant than it seems -- if your glaze
had very little alumina to begin with, even a little
extra can make it change texture, or a little less
might make it somewhat runny.
And the difference in K/Na makes G-200 potentially
a little more likely to melt at a slightly lower
temp than Custer. But the higher alumina amount does
the opposite -- and here lies the secret of this
substitution:
Getting to a working, reliable glaze, relies not
on absolute ingredients as much as relative
concentrations of fluxes, stiffeners, and glass-formers.
The Custer to G-200 swap is of two similar types of
material (potash feldspar) with similar distribution
of material and, more importantly, differences that
make them come closer to identical behavior than
could initially be expected.
If you see and difference at all, it'll probably
be that the version of the glaze with G-200 is very
slightly runnier than the one with Custer (at least
that's been my experience).
So my answer is -- try a swap of these two without
changing anything else in a small test batch -- it'll
probably work just fine. Especially if the recipe uses
15% or less feldspar.
If you want to try to 'fix' a glaze with this
substitution, adjust the clay content first --
get the overall alumina on target first -- and
then because virtually all of our glazes involve
adding 'pure' silica, adjust the silica up or
down as needed.
Now I'm sorry for rambling, but I don't have
the time to make this message shorter. The
next issue I wanted to address is whether any
glaze recipe can be used without colorants.
My answer is no. Some recipes rely on the
stiffening effect of zirconium, or the fluxing
effect of copper or cobalt, for example to
mature and stick to the pot both.
My personal experience with testing Ron'n'John's
Glossy base #1 and Calcium Matte #2, however,
strongly implies that you can beat on these two
recipes like they were a drum without doing any
harm. They appear to have been formulated at that
'center of the range' where you can go a little
off and still get highly similar and completely
satisfactory effects.
Now this gets us to the last issue I can
perhaps help a little on -- can you get a
clear matte finish glaze? Fundamentally,
what gets you a buttery or satiny surface is
a pattern of tiny irregularities in the surface,
often caused by mini to micro crystallization
under the surface. Thess patterns of
irregularities (some of which are quite
attractive viewed under a loupe) will reflect
some incoming light in different directions,
and possibly set up a pattern of diffraction
from the light returning from the clay surface.
This makes the glaze progressively less clear as
becomes more textured.
So clear glossy is easy, and cloudy or opaque
glossy is not hard, but clear matte is extremely
difficult -- and by the time it has a satiny
surface, it probably won't be too clear.
I hope some of this is helpful. If you want
a particular recipe reformulated in substitition,
I'd be willing to give it a try, though Ron Roy
almost always gets it closer than I do. There
is also a lurker on Clayart -- I will not mention
her name to protect her anonymity -- who has a
program that will automatically calculate
substitutions, a simply brilliant piece of
software, that (1) only runs on a less common
operating system, and (2) doesn't yet have perfect
error trapping. If she ever finishes it, everyone
will want this software. In the meantime, if you
give me a problem that's too tough for me to get
into, I can pass it to her.
Good luck -- happy experimenting -- Steve Slatin
--- In clayart@yahoogroups.com, Jackie Shaw wrote:
>
> Hi All,
>
> I am a novice at glaze mixing, but have mixed several successful
glazes
> from recipes (MC6G and others). I would like a CLEAR, buttery or
satin
> matte glaze, ^6, for use on stoneware.* (I've been sucked into the
Clayart
> Archives -- such a great resource for so many things -- for several
hours
> looking for such but no luck).
>
> Can the base glaze of ANY recipe be used as a clear glaze? Or might
some
> of the basic ingredients--or combinations of them-- make it
opaque? (This
> question will probably verify my novice status!) I am considering
using RR
> & JH's "High Calcium Matte/Semimatte Base 1.
Ivor and Olive Lewis on sun 18 nov 07
Dear Jackie Shaw=20
You tell us << I would like a CLEAR, buttery or satin matte glaze, ^6, =
for use on stoneware. >><clear glaze? Or might some of the basic ingredients--or combinations of =
them-- make it opaque?>>
This request and your question get right down to the fundamental =
processes of glazemaking and why some effects are impossible to achieve. =
In postings made earlier this year the same question was asked and =
several people suggest that the best way was to sad blast a transparent =
glaze.
The essence of a Base Glaze is that the ingredients will fuse to give a =
fluid that will cool to make a transparent glass that adheres to the =
clay on which it is placed.
Certain ingredients, when added to such a Base Glaze dissolve, then on =
cooling precipitate as very small crystals that disturb the passage of =
light into and from the vitreous material. Talc, which supplies =
Magnesium oxide and Whiting, which supplies Calcium oxide are two =
compounds that form silicate crystals that are thrown out of solution =
when the molten glaze cools. The quantity of each put into a glaze will =
determine the degree of opaqueness and mattness.
Sorry, I cannot answer your felspar question.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Alisa Clausen on mon 19 nov 07
>I am a novice at glaze mixing, but have mixed several successful glazes
>from recipes (MC6G and others). I would like a CLEAR, buttery or satin
>matte glaze, ^6, for use on stoneware.* (I've been sucked into the Clayart
>Archives -- such a great resource for so many things -- for several hours
>looking for such but no luck).
>
>Can the base glaze of ANY recipe be used as a clear glaze? Or might some
>of the basic ingredients--or combinations of them-- make it opaque? (This
>question will probably verify my novice status!) I am considering using RR
>& JH's "High Calcium Matte/Semimatte Base 1.
>
Hi Jackie
You have recieved several answers to your question, and I would like to
say a couple of things more.
As said, glazes without colorants are a transparent base of sorts. Some
clearer than others. However, I have found that, some glazes without
their intended coloring oxides, will have crazing problems. We are back
to the flux impact of oxides in glaze bases. I think if there is a
surface of a glaze you happen to like, try it as a base and run it through
a glaze calc. program. Both the glaze calc. information as far as the
Al:Si ratio with regard to how glossy or mat the base is and the COE will
be telling, as will also the glaze test you have fired. If there is
crazing, you may be able to adjust the base to fit your body without the
oxide colorants.
As far as Feldspar, both the Suster and G-200 are Potash. I use a
Feldspar that would comes closest to C6 which is a sort of half and half
Soda and Potash, as a sub. for the often called for Potash Feldspars in
cone 6 glazes. My results are good.
I would agree that a mat clear is a tricky glaze effect. Transparence
could easily be crossed out by a mat nature of a glaze. But I have a clear
base that after some development and testing, I have renamed Dolita Clear
for my friend.
This is the recipe and I think it is a really good semi mat silk
transparent that both colors well and goes well over oxide washes and
underglazes. You can see a photo of it on my flickr page at
http://www.flickr.com/photos/glazes/sets/
the set is opacity tests and it is the first photo in the set.
Recipe Name: Dolita Base (Alisa's Base)
Cone: 6 Color:
Firing: Surface: Semimatte
Amount Ingredient
27 Frit--Ferro 3124
30 Kaolin--EPK
18 Silica
10 Ball Clay--Old Mine #4
15 Dolomite
100 Total
Unity Oxide
.107 Na2O
.017 K2O
.299 MgO
.578 CaO
1.000 Total
.622 Al2O3
.2 B2O3
.009 Fe2O3
3.291 SiO2
.01 TiO2
.001 P2O5
5.3 Ratio
6 Exp
Comments: a semi mat base for coloring with oxides
-----------------------------------
Calculations by GlazeMaster=99
www.masteringglazes.com
------------------------------------
Best regards from Alisa in Denmark
al
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