Paul Raymond on mon 29 sep 03
Ron, (or other glaze gurus),
I am getting ready to begin a round of testing in order to develop my glaze
pallet. I have been reading your (&JH's) book a lot and making spread sheets
in excell to keep track of what I am doing and spending etc. In compiling
some info I realized that the glaze called Glossy Base Glaze 1 (pg 92) has
exactly the same ingredients as Glossy Clear Liner Glaze (pg 97). The
difference being that the percentages of the materials varys. Specifically,
GBG 1 calls for 10% wollostonite and 11.5% talc. GCLG has woll at 15% and
talc at 6. The only other difference beween the 2 recipes is 1/2% diff in
silica. This is fairly small so I assume it is a negligilbe difference.
You write that the difference beween these 2 glazes is the the first is a
bit milky while the liner glaze is clear. So, according to my research, the
decrease in talc for GCLG reults in this glaze being clear becase much more
than this would begin to cloud the glaze (hence the milk in GBG 1) due to
the fact that large amounts of talc contributes to the glaze becoming
opaque. Is that correct?
Now with wollostonite, I could not find a clear definition of this material
and it's properties. I am curious what it does. I did find the chemical
compistion you provide in the book and through that deduced that
wollostonite contributes glass, (over 50% of the stuff is silica) and
hardness due to the calcium (over 42%). Is this correct?
Finally, can one say, based on looking at these ingredients and unity
formulas, that these glazes are very glassy and rather durable? They each
read over 3 in Si and over .5 in Ca.
By the way, I think your book is excellent. I have a decent amount of
experience with designing glazes (for a novice) and it really clears up a
lot of questions. I appreciate have the unity formulas available for really
being able to analyze a glaze. I hope my observations above prove to be on
target. Looking forward to reading you response. Thanks for your time.
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iandol on thu 2 oct 03
Dear Ron Roy,
You say <a glass former and CaO is a flux at cone 6.
Talc is a source of silica and magnesia - silica again being a glass =
former and MgO is a flux. >>
Sometimes I wonder if we are not misrepresenting the facts or misleading =
others by abstracting real compounds, which are introduced into our =
recipes, when we represent them as molecular oxides. I accept that it is =
common practice to speak of these entities as you have done. But there =
is an inference that decomposition takes place before these minerals can =
make a contribution to the creation of a glaze.
Am I correct in forming this opinion?
Ivor Lewis. Redhill, South Australia
Paul Raymond on thu 2 oct 03
Well, I took your suggestion:
"< - if you want to try the two glazes
using different materials I will do it for you.
Whiting for wollastonite
Dolomite for talc and wolastonite
Custer for G200
Ball clay for EPK
Frit 3195 for frit 3134>"
and did a glaze calculation for the materials you suggested to use as
substitutes. Now, I'm not really sure what i am doing yet so I simply
tweeked the levels of materials until I got close to the numbers for the
glossy clear liner glaze. Much of this tweeking took the form of, "well, I
think the frit will have a lot of Si and so will the Custer. The OM#4 is
clay , to give the glaze some 'body' and Al. The Dolomite must act as a flux
along with whiting..." etc.
Anyway, this is what I came up with:
OM #4, 9.5
After runnig the numbers for a while and not getting a high enough Si:Al
ratio I added silica, 18. This brought the total to 100.
I ended up with a ratio of 8.73, compareed to 9.15 for the original GCLG.
The unity formula says that my SiO2 is at 3.286. Am I on the right track,
Was the addition of Si appropriate? I should tell you that I used
Glazemaster and the materials anaysis supplied within. I don't have any of
my own materials yet so I could not input that information.
So, what do you think? Am I on the right track?
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Ron Roy on mon 6 oct 03
Hi Ivor - I went on to say - that because they are already combined the
glaze - it will take a bit less heat to melt it - would that not imply they
don't need to be undone before they can recombine - would that not take
more heat - not less?
>You say <>glass former and CaO is a flux at cone 6.
>Talc is a source of silica and magnesia - silica again being a glass
>former and MgO is a flux. >>
>Sometimes I wonder if we are not misrepresenting the facts or misleading
>others by abstracting real compounds, which are introduced into our
>recipes, when we represent them as molecular oxides. I accept that it is
>common practice to speak of these entities as you have done. But there is
>an inference that decomposition takes place before these minerals can make
>a contribution to the creation of a glaze.
>Am I correct in forming this opinion?
>Ivor Lewis. Redhill, South Australia
15084 Little Lake Road
iandol on wed 8 oct 03
Dear Ron Roy,
You ask << ...I went on to say - that because they are already combined =
the glaze - it will take a bit less heat to melt it - would that not =
imply they don't need to be undone before they can recombine - would =
that not take more heat - not less?>>
Not sure about this one Ron, I always have trouble with sentences which =
contain a double negation.
What is wrong with each of the ingredients in turn or simultaneously, =
dissolving into the material which has melted first as temperature =
rises. As an analogy I would propose taking water at almost freezing =
point and adding an excess of sugar. The sugar "Melts" into the water =
and more of it "Melts" into the solution as temperature rises. I prefer =
to say the sugar is "Dissolving". I think Frits melt first and provide a =
solvent for the other materials.
But I asked <entities as you have done. But there is an inference that decomposition =
takes place before these minerals can make a contribution to the =
creation of a glaze. Am I correct in forming this opinion?>>... =
regarding your presentation ...<and calcium. Silica is a glass former and CaO is a flux at cone 6. Talc =
is a source of silica and magnesia - silica again being a glass former =
and MgO is a flux. >>
I think we have contrasting ways of dealing with information. I like the =
Ivor Lewis. Redhill, South Australia