Glaze Test City

[oldlady]

if you have a few dollars left, maybe you would want to take some lessons from a potter who works with crystalline glazes. look at the website for Pottery Boys in Florida.  

 

there has to be one in your neighborhood.

[High Bridge Pottery]

Joel:

 

I think you and I would get along very well: I have fired over one ton of porcelain clay testing cone 6 and 10 crystalline glaze. I had been saving up for nearly 40 years to buy an RV when I retired. Finally got to the age to buy it and decided I did not want another item I had to take care of. So I spent it on kilns, equipment, clay and supplies. The problem being I had never touched clay or fired anything in my life. So I spent the last four years reading books, studying chemistry, and throwing away a lot of mistakes. I primarily work with cone 6 crystalline at this point. I have been testing my drip-less recipe for the last six months and have it dialed in fairly close. It freaks out my crystalline friends that I am firing this glaze without catchers. Although I do some vertical pieces, I am rather fond of the custom geometric patterns that I have created. I use my professional CAD system, along with my plotter/ printer ( 24" x 36" paper) to make the patterns.

Now that I have the glaze formulation correct, I have moved to formulating a custom porcelain recipe I lovingly call: crystal clay. One of the smartest moves I made was relearning chemistry. I can calculate covalent and ionic bonds without having to mix anything. You might find quantitative kinetic reactions and formulation an interesting topic. Still learning these topics, but my old tired brain is starting to click. Thankfully there are online algebra calculators so I do not have to figure it out in my head.

 

Glaze Nerd

 

Welcome to the forum Glaze Nerd, I am sure we would get along great. At least the internet lets us communicate, always good to have another glaze nerd about. If you ever feel like sharing any R&D I would love to read it. Think you made a good choice over the RV but not sure about less looking after, as long as you are enjoying it.

 

I will have to look into that, I have always wanted to be able to see a glaze as lego blocks that you can build up in certain 'bonds'. I assume that is sort of what you mean.

 

Are you 3D printing or is it a slab flat pack to shape thing?

[Tyler Miller]

glazenerd,

 

Welcome to the forums!  I'd be really interested to see how you arrive at the TTT diagrams you use for a given glaze recipe (I'm assuming this is what you mean by quantitative kinetic reactions).  I've used them regularly in heat treating, never thought to apply them to glaze chem.

[Tyler Miller]

Thanks for the welcomes- one and all.

 

Tyler: part of quantitative kinetics is rate laws: I use it primarily to figure out concentrations, factoring surface areas: which in turns gives the foundation for temperature. It is well known that most of the products / elements we use are not pure. In essence, it gives the math formulas to convert to empirical formulation. So kinetics as I use them are: temperature = rate of reaction, reactant concentration, and surface area. The accepted basis being: reaction rate doubles for every 50F degree climb in temp. There are many areas of chemistry I skim over- only trying to learn what directly relates to glaze/clay chemistry.--- and I am still learning.

 

 

Glaze nerd- Tom

 

Forgive me, I'm familiar with the principles you're talking about, but I'm having trouble trying to picture how you're using what you're talking about in a real world ceramics example.  I thought you were talking about TTT diagrams, which would allow you to predict appropriate/optimal down-firing rates for crystal formation.  That is to say, TTT diagrams would be an appropriate and expected way to represent the kinetics of glass/crystal formation.  

 

But you seem to be deal more with a theoretical prediction of eutectic formations and composition?  Is this correct?  Could you provide an example of what you're doing?  I picture you using eutectic diagrams and associated formulae to arrive at appropriate melt temperatures.

 

How would you say this benefits your process over using the conventional triaxial and quadraxial blend experiments?

 

Forgive all the questions, but I've never heard of anyone approaching glaze chem the way you are.

[Tyler Miller]

Thanks for the clarification, that makes much more sense. I should point out willemite is actually Zn2SiO4. That is, two zinc oxides and one silicon dioxide in covalent lattice. Your formula would indeed imply an ionic bond, but the correct formula is two zinc oxides in covalent lattice with one silicon dioxide. There's also no extra anions in SiO4--it's just a more accurate way to reflect the covalent bond. SiO2 implies discrete O=Si=O molecules, like CO2, but in reality it looks more like:

 

O-Si-O-Si-O

I I I I I

Si-O-Si-O-Si

I I I I I

O-Si-O-Si-O

 

And on and on in all directions until you hit the physical limits of the chunk of silica. That may help your research. Edit: the bunches of I's are supposed to represent single bonds between the Si and O along the vertical (y) axis. It formats properly in the editing window, but it doesn't work once posted.

[Tyler Miller]

The glaze itself is all a covalent lattice--ish (in reality, it's the grey area in between the two and the fact that we're occupying this grey area is how we get things to work via polarities). The fluxes are where you find the ionic bonds. One side is more negative, the other more positive, and it's their polarity that lowers the melt temp. And that polarity is how the fluxes interact with the lattice of SiO2 and Al2O3. Think of it like water and salt. Water molecules have a natural polarity which forms a lattice with the Na+ and Cl- ions, which lowers the melting temperature. The fluxes we use in ceramics are like the salt, the glass former is like the water.

Does that make sense?

[Tyler Miller]

Tom,

 

I think you're distracting yourself with research that doesn't really apply.  I can't think of how Gibbs free energy is necessary to make any predictions.  Glaze chemistry is just the chemistry of dissolving things into a liquid and cooling it.  That's really it, melting, dissolving, and crystal growth.  In theory any glaze could be crystalline--matte glazes are crystalline at a microscopic level.  

 

 

I suggest you direct your research into the Time-Temperature-Transformation curves I've mentioned above, and the related Continuous Cooling Transformation curves (TTT diagrams and CCT diagrams).  You'll need to do some digging through research (as well as your own) experimentation, but once you have enough data, you should be able to construct your own curves for cooling rates to optimize your crystalline glazes.  These curves will allow you to make bigger crystals and predict what percentage of the glaze will be crystalline (vs. vitreous).  In short, they'll tell you how to downfire to get results.

 

Check out this homework from a college class, the assignment is to sketch a TTT diagram for 1 ppm of crystalline content in a vitreous material, then 1% crystalline content.  http://web.mst.edu/~brow/HW3_ans.html

 

Crystalline glazes aren't really that unique or special.  Glass makers have been moaning about crystals in their glass since the first guy melted sand and wood ash together.  Any glaze can crystalize if you cool it at a rate that promotes crystal growth.  The zinc oxide crystalline glazes are just a (relatively) easy way to let that happen.  There are a lot of myths, like that alumina is bad for crystal glazes, but this isn't necessarily the case.

 

You're going to be frustrated by the lack of research in these areas, though.  What you're hoping to do is relatively new research, and eutectic diagrams (binary, ternary, etc.) and TTT curves have very real limitations in real world applications.  Lots of experiments ahead to get the formulae to where they're useful.

 

You're blazing new territory, my friend, I'm excited by that.

 

-Tyler

[curt]

Whew! Thanks for that last link, Tyler.  As the back and forth went on, I was beginning to feel like a small child at the circus jumping up to try and grab the helium balloons which had just escaped from my hand!  Usually that never ends well, but your "homework" let me claw back some of my technical ego...  

 

Seriously loving this discussion, though.  While I am no acolyte of the crystalline cult, I can see the widespread applicability of the underlying framework to large swaths of glazeland.  About every 10th technical article I read on glazing teases me with "...if only you knew a little bit more about the effects of cooling all this and more could be yours..."

 

I see references to Shelby in the homework.  Is that the Shelby that wrote the glass textbook?   Much of the discussion you guys have been having reminds me of stuff I saw recently when researching bubble formation, which ended up in a recent thread in this forum with High Bridge and others.  Seems the glass guys have plenty to teach us about glazing.  

 

Any other texts, articles, etc. which may help us innocents keep up with the dialogue? 

[Tyler Miller]

Whew! Thanks for that last link, Tyler.  As the back and forth went on, I was beginning to feel like a small child at the circus jumping up to try and grab the helium balloons which had just escaped from my hand!  Usually that never ends well, but your "homework" let me claw back some of my technical ego...  

 

Seriously loving this discussion, though.  While I am no acolyte of the crystalline cult, I can see the widespread applicability of the underlying framework to large swaths of glazeland.  About every 10th technical article I read on glazing teases me with "...if only you knew a little bit more about the effects of cooling all this and more could be yours..."

 

I see references to Shelby in the homework.  Is that the Shelby that wrote the glass textbook?   Much of the discussion you guys have been having reminds me of stuff I saw recently when researching bubble formation, which ended up in a recent thread in this forum with High Bridge and others.  Seems the glass guys have plenty to teach us about glazing.  

 

Any other texts, articles, etc. which may help us innocents keep up with the dialogue? 

Curt,

 

The homework does indeed refer to Shelby's Introduction to Glass Science and Technology.  The TTT curves in the homework are lifted from page 17 of Shelby.  If you don't want to buy the book, Brow's lecture notes for his ceramic engineering 103 course are a serviceable substitute.  Link:  http://web.mst.edu/~brow/cer103.html

 

Note that the links to each chapter's course notes are dead, because they refer to his old "live" website.  If you add the individual page address to the "http://web.mst.edu/~brow/"you can access all the PDFs.  E.g. adding the "PDF_Intro.pdf" of the dead link, so that you have "http://web.mst.edu/~brow/PDF_intro.pfg" will get you the introductory lecture notes.

 

Give me a day or two and I'll track down some stuff on eutectics.  I'm not really a glass guy, I'm a metallurgy guy, and that's how I'm familiar with this science, TTT diagrams are indispensable for heat treating steel as each alloy has its own cooling curve.  The ceramic and glass implications are rather new.

 

I hope this helps you navigate our discussion.

 

-Tyler

[Bob Coyle]

Rate laws!... Gibs free energy!... I'm back in P-Chem!

 

Seriously though, trying to predict glaze behavior by more or less first principals is in my opinion, like using thermodynamics to predict the weather.  The complexity of more than a dozen different chemical entity's interacting in a molten solution would require some real hairy computation for even coming close to predicting anything.

 

This ground has already been plowed by geologists trying to understand rock formation and by scientists trying to develop better glass products.. both of which glazes are. I myself have downloaded many articles on these subjects and realize that the math of predicting behavior of even three or four component systems requires writing a complex computer program to crunch the permutations of possible chemical interactions that may take place.

 

I think Tyler summed up most of the research that has been done on multi-component glasses. the researchers found ....

 

The glaze itself is all a covalent lattice--ish (structure.)

 

Before anyone says a word more, I highly recommend they sit through this lecture on glass given at MIT. It is the clearest and best first principle-ish explanation I have run into... happy watching!    

[Min]

I'm going to have to agree with Bob "The complexity of more than a dozen different chemical entity's interacting in a molten solution would require some real hairy computation for even coming close to predicting anything."

 

I keep coming back to Aristotle "The whole is greater than the sum of its parts."  and Yogi Berra "In theory there is no difference between theory and practice. In practice there is."

 

Interesting posts, practical or theoretical though? 

[Bob Coyle]

And if that didn't scare you off, then lecture 22 wraps it up

[High Bridge Pottery]

Well if there is ever a quiet moment over Christmas I have lots of reading to do

[Tim T]

It's good to have some discussion of the underlying theory - even if reality is too complex to model, understanding a simplified model can still give useful insights into what is happening when developing a glaze. And I have found it hard to find sources for this - most current glaze books are recipe books or purely empirical, and those that are more technical like Eppler and Tichane still only touch the surface, so many thanks for the references given here.

 

One thread I'll be starting in the next few days is on fluorine in glazes - I've got to gather my notes into one place first, but it doesn't seem to work as described in the few references available and working this out may appeal to some of those here, as I've got some interesting effects (and some major disasters!)

[Bob Coyle]

Boy Tim, sounds like something us glaze nuts could sink our teeth into!

Looking forward to the post.

[glazenerd]

Tim:

 

and for those reasons I turned to chemistry. Have yet to find a single glaze book that truly defined crystalline glaze. I see phrases such as " has an affinity for." or "forms in a glassy matrix." That would satisfy most people, but not a glaze nerd. The hardest part of chemistry is figuring out what applies and what does not. Then figuring out of the sections that do apply, which laws, rates, and equations to use. For the record: frit is getting assigned O value: not even going to attempt sorting out the 7 ingredients. I am focusing only on silica, zinc, and lithium as a base: metal oxides are in reality the easy part. Actually a bit of reverse engineering so to speak: because I already know temps. In particular: Hess Law>reverse reactions- which should give me a kJ/mol. The only reason I have any interest in Gibbs- the rest can go in the trash. Once I get the info together, my good friend the trig guy can work the equations- I am not that smart. Truthfully, not even sure the chemistry route will even work: but it's the only route available that I am aware of.

 

Glaze Nerd...... and a Merry Christmas to one and all.

[glazenerd]

Going to have a very long list of numbers here shortly- will drop the bomb and will pay the first chemist that can decipher them. An all expense paid weekend to Antarctica, with 20 lbs of penguin food. Actually, going to have many questions.

 

 

Nerd