Ron Roy on wed 1 oct 03
Hi Paul,
It is not easy to compare recipes - in fact I would say impossible - it is
a good reason to understand the Seger Unity Molecular Formula.
If you compare the unity formula of those two glazes you will see the
differences as they really are.
I fact they are very similar and I would expect them to resemble each other
- perhaps the Glossy clear might be a bit more stable because of the extra
SiO2 and Al2O3.
The glossy Clear has a higher expansion than the Glossy base 1 - because
the MgO is higher in GC bas 1 and it has a lower expansion rate that any of
the other fluxes.
The MgO in GB#1 is high and it may be responsible for less melting. We are
talking now about which glaze would have the better balanced fluxes. I am
assuming the better melt in GB clear liner is due to the more balanced
fluxes in spite of the higher SiO2 and Al2O3.
Perhaps you would care to do an experiment to see which is melting more.
On a test tile put 4 layers of each glaze - full dip for layer 1, on top of
that a 3/4 dip for layer 2, and a half dip for layer three. This will tell
you which glaze will run the most and give some indication of which is
melting more - protect your shelves!
Wolastonite is a source of both silica 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.
If you study the unity formula you will see - the oxides are separated into
three distinct groups - fluxes, stabilizes, and glass formers. Each has a
role to play in glazes.
Perhaps your question is - why use Wollastonite instead of Whiting to get CaO?
Whiting is cheaper for sure. There is perhaps some advantage in that
wollastonite - because it is already combined CaO and SiO2 will need a
little less heat to melt than if you used Whiting and Silica. On the other
hand wollastonite has only a small LOI (loss on ignition) while Whiting has
a whopping 45%.
Neither is a big factor in my opinion - 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
Not hard to do if you know how to use calculation software and have good
analysis.
I have rambled on a bit - even answering questions you didn't even ask -
can't help it sometimes - there is some passion involved - forgive me. I'll
be glad to add to this if you have more to ask.
Thanks for the kind words about our book - it was a work of love and it is
always a wonderful feeling to hear from those who appreciate it.
RR
>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.
>
>Paul Raymond
>Franklin,TN
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on wed 8 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:
>
>Whiting, 7
>Dolomite, 6.5
>Custer, 23.5
>OM #4, 9.5
>3195, 35
>
>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?
>Thanks,
>Paul Raymond
Hi Paul,
Good for you for trying this - now don't get discouraged because of what I
am going to say about your efforts - this is an excellent chance for you to
make some real progress.
First of all I simply entered the same amounts of the new materials -
Custer for G200, 3195 for 3134, Whiting for Wollastonite, Om-4 for EPK, and
Dolomite for Talc.
I then compared the Seger molecular formula of the two glazes.
The CaO in the new glaze is a little high.
The MgO is low
The KNaO is too low
The B2O3 is just a tad high (this makes sense because the analysis for 3195
has about the same as 3134) That means you will need about 20% in the final
glaze - you have 35% so your boron is going to be too high.
Alumina is about the same.
Silica is low - this makes sense because we took out both wollastonite and
talc - both of which have SiO2 in them - and we subbed in Dolomite and
whiting - both of which have very little.
So now I'm thinking - what to do first - get the fluxes right - keep the
B2O3 the same - and them top off the alumina - then adjust silica last.
I'll skip the frit for now - it's real close - I'll work on getting the MgO
up for starters. I have to use Dolomite because thats where the MgO is.
As I increase the dolomite the MgO goes up - but - when I get the MgO right
I see I have lost some CaO - OK I need less - now I take out some whiting
to get the CaO down - surprise - the MgO goes up. So back to the dolomite
and take some out - then back to lower the dolomite - then back to the
whiting - till they are right.
Now the KNaO is about right - why? Because there are only 4 fluxes and they
have to add to 1.0 - so if the MgO and the CaO are right then the KNaO has
to be at least close.
Whoops - the B2O3 is up - sure - because the total is now only 93.5 and the
amount of frit is still 20 so it's more than 20% now.
OK - I lower the amount of frit till the mols of B2O3 are equal to the
original recipe.
Surprisingly this does not make much difference to the fluxes - MgO is up a
bit so I adjust the dolomite down a bit - the B2O3 goes up a bit so I lower
it a tad.
Now all the fluxes are equal, the B2O3 is equal, the Al2O3 is high and the
silica is high.
To lower the alumina I have to lower the clay - easy - Just keep lowering
it till the numbers match up - I can set the raising or lowering increment
on my calculator -I usually keep that at 0.5 for glazes - makes it easy to
adjust amounts of materials.
Almost done - the SiO2 is a bit high so I decease the silica till they are
equal or very close.
I now notice that the ratio and expansion are off a little more than I like
- so I take a look at the formula in % and I see the alumina is a bit low
so I raise the OM#4 by 0.5 and the silica by the same amount. Now the ratio
is only .05 different and the expansion is very close as well.
The total of the recipe is 77.0 so I now tell my program to make it 100. I
now round the numbers of to the nearest 0.5 - watching the mols - then I
check the % of each oxide in the molecular window to see if I can get it
closer - make a few minor adjustments till the ratio and expansion are real
close and I'm done - it's gonna be the same glaze 90% of the time -
especially if it's a balanced glaze.
In this case the original ratio is 9.16 and the revisions is 9.16 - the
expansion of the original is 424.38 and the new one is 423.05.
Your numbers may differ because you are not using the same analysis that I
am using. If they are way off suspect your materials analysis in you MDT.
RR
>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:
>
>Whiting, 7
>Dolomite, 6.5
>Custer, 23.5
>OM #4, 9.5
>3195, 35
>
>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?
>
>Thanks,
>
>Paul Raymond
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
