Stull Charts, Flux Ratios, Silica:Alumina Ratios - Open Discussion

[Min]

Starting a new thread to discuss Stull, Flux Ratios, Silica:Alumina Ratios and the like that came up in this thread as it started to go off on a tangent into these areas. 

All comments, theories and hypothesis welcome.
Do you look at Stull or ratios or limit charts or none of these? How useful do you find glaze calc software if you you it?

Stull chart, do you see where your glaze(s) are on it and do you find it helpful in predicting a glazes attributes or altering a glaze?

Flux ratios, do you try and stick within 0.3 R20:0.7 RO ? Do you use this ratio for high calcium, barium, strontium, or magnesium matte glazes?

Silica to alumina ratios, do you use these to predict or alter gloss levels?

Boron levels, have you found “high” boron levels have an effect on glaze durability? Have you found glazes really high in boron are prone to crazing even though COE figures decrease with increasing amounts of boron? 

Do you choose not to use glaze chem calculators and rely on  line blending or a similar type testing or a shotgun approach testing and altering  a glaze?
 

 

 

 

 

Edited January 8 by Min

[High Bridge Pottery]

I'm not convinced there's much evidence that 0.3:0.7 is the most durable ratio. I mean even in that ratio there's so many different fluxes included that there's too many variables for it to be a useful rule.

[Bill Kielb]

51 minutes ago, High Bridge Pottery said:

I'm not convinced there's much evidence that 0.3:0.7 is the most durable ratio. I mean even in that ratio there's so many different fluxes included that there's too many variables for it to be a useful rule.

I would definitely agree - it should not be viewed as a rule for sure. Even Katz believes working within a range is practical. Definitely more research, but something to help design within and when significantly outside a reasonable range that knowledge would hopefully cause folks to investigate. For folks that are science oriented, proving something true is usually impossible just because all conditions never can be accounted for. 

From a design standpoint I find it as helpful or a bit more than relative references we see in glazes such as High, as in high alkaline - how much is high, who knows? Same with high calcium matte or high alumina matte. They are all somewhat helpful references though as folks sought to characterize for the benefit of others so totally dismissing those efforts probably not productive or fair.

So more successful testing under as many conditions as practical likely would increase confidence for sure, dismissing the results entirely, without reasonable contrary testing probably not the best path either.

[Morgan]

9 hours ago, High Bridge Pottery said:

I'm not convinced there's much evidence that 0.3:0.7 is the most durable ratio. I mean even in that ratio there's so many different fluxes included that there's too many variables for it to be a useful rule.

100% agree

[C.Banks]

I wish I could remember @Min who proposed an alternative to the UMF. I have a few stacks of old magazines and perodicals I flip through. I have a suspicion the most relevant article is at the bottom of one of those stacks. Next time I'm in the shop I'll try to find it.

I know there are other references but they could simply be letters to the editor.

 

[Roberta12]

I took a 3 day in person workshop in 2022 from Matt Katz in Denver.  He explained the UMF and Stull chart.  That was an eye opener for me.  I will admit I barely have a grasp on the  0.3 R20:0.7 RO But I did immediately sign up with Glazy and I do turn to it when I am either trying a new glaze or looking at my standby glazes with a fresh eye.  I try to find the sweet spot on the UMF chart depending on the glaze I am looking at.  I would like to take a deeper look at glazes either with Sue Mcloed  or Matt and Rose Katz, but my time for that has been limited the last few years with family stuff.  It's still on the docket for me, perhaps this year it will happen.  But to go back to the original question from @Min  I do look at the UMF.  And if a glaze is not where I would like to see it on that chart, but I still want to try it, I do a fair amount of testing.  Freeze, boil, lemon, dishwasher, micro, all those things, just to see.  One example was a glaze called Ayumi Aqua.  We used it at a workshop.  I really loved it.  Nice feel, soft color, I mixed a small batch.  It was in the "crazed" part of the chart.  I have not been able to make it craze on any clay, but it does not perform well on any clay.  Pitting, bubbling etc.  So, there you are.  I should have "listened" to the chart.

Roberta

[Min]

@C.Banks, is this a snippet of the UMF article? I can't access the full article, if it is maybe somebody can find it? It's from William Carty , Matt Katz and John Gill.

The Unity Molecular Formula Approach to Glaze Development

• March 2008
• Ceramic Engineering and Science Proceedings 21(2):95 - 107

DOI:10.1002/9780470294611.ch10

• In book: Materials & Equipment/Whitewares: Ceramic Engineering and Science Proceedings, Volume 21, Issue 2 (pp.95 - 107)

[davidh4976]

6 minutes ago, Min said:

@C.Banks, is this a snippet of the UMF article? I can't access the full article, if it is maybe somebody can find it? It's from William Carty , Matt Katz and John Gill.

The Unity Molecular Formula Approach to Glaze Development

• March 2008
• Ceramic Engineering and Science Proceedings 21(2):95 - 107

DOI:10.1002/9780470294611.ch10

• In book: Materials & Equipment/Whitewares: Ceramic Engineering and Science Proceedings, Volume 21, Issue 2 (pp.95 - 107)

I just had to find the full document: https://aura.alfred.edu/server/api/core/bitstreams/182c2504-e6ac-42f7-bb12-34492c950d5f/content

 

[C.Banks]

1 hour ago, Min said:

@C.Banks, is this a snippet of the UMF article? I can't access the full article, if it is maybe somebody can find it? It's from William Carty , Matt Katz and John Gill.

The one I'm thinking of is from an old ceramics monthly from the  ? 90's?

The mention of calcium is interesting. Growing up we used forms of whiting (and feldspar) without any concern for R2O:RO. Our glazes did just fine but it turns our they were way outside 0.3:0.7.

Edited January 9 by C.Banks

[Bill Kielb]

53 minutes ago, C.Banks said:

Our glazes did just fine but it turns our they were way outside 0.3:0.7.

It would be interesting to see just how many departed significantly. Lots of old glaze recipes fall into a reasonable range around 0.3:0.7. I would love to see real comparison data on this, anecdotal often has the potential for perception bias.

[Min]

On 1/9/2024 at 9:44 AM, C.Banks said:

The one I'm thinking of is from an old ceramics monthly from the  ? 90's?

I'll try and do a search online for it in CM through ICAN, do you remember the author or anything else about it? 

Thing about flux ratios that doesn't make sense to me is using them to look at microcrystalline glazes. If a microcrystalline glaze is formed via the mechanism of the excess MgO, CaO, SrO, BaO, Al2O3, TiO2, ZnO, or MnO (or combination of these) that do not stay within the eutectic during the cooling phase of the glaze matrix then how does one measure for this? Same reason that COE figures don't work on semi or matte glazes. 

 

Edited January 11 by Min

[C.Banks]

3 hours ago, Bill Kielb said:

It would be interesting to see just how many departed significantly. Lots of old glaze recipes fall into a reasonable range around 0.3:0.7. I would love to see real comparison data on this, anecdotal often has the potential for perception bias.

I've been tempted to put in the work and see how the ratio holds up. It would make for good content.

[C.Banks]

3 hours ago, Min said:

I'll try and do a search online for it in CM through ICAN, do you remember the author or anything else about it? I'll read the article you linked when I have time in the next few days.

Thing about flux ratios that doesn't make sense to me is using them to look at microcrystalline glazes. If a microcrystalline glaze is formed via the mechanism of the excess MgO, CaO, SrO, BaO, Al2O3, TiO2, ZnO, or MnO (or combination of these) that do not stay within the eutectic during the cooling phase of the glaze matrix then how does one measure for this? Same reason that COE figures don't work on semi or matte glazes. 

 

I don't remember much about it other than gave me reasons to avoid decyphering the UMF.

I aquire magazines and some years I read less than others so this goes back at least three years and probably closer to five.

Something I didn't appreciate until only somewhat recently is just how many eutectics exist. It's possible small systems are forming within larger eutectics? This will expose how little I know but I'm ok not knowing things.

 

 

[Min]

7 hours ago, C.Banks said:

I don't remember much about it other than gave me reasons to avoid decyphering the UMF.

I aquire magazines and some years I read less than others so this goes back at least three years and probably closer to five.

I went through the Techno File topics from Ceramics Monthly and the only one that struck me might possibly be it is the "Ingredients' Roles"  article written by Steve Loucks in the Nov 2021 issue. It's behind a paywall but you can access 3 free articles a month.  Basically Loucks looks at glaze components and lists them in a specific sequence of spars, fluxes, clays and glass formers then looking at the fired glaze in relation to what the ingredients do and what influence they have on the glaze. Alterations are then made to the base glaze to see how the different components change the base. There is a brief comment on UMF but not much. Possibly what you were referring to?

Edited January 10 by Min
bad analogy deleted

[GEP]

My “for what it’s worth” contribution to this discussion: 

The glaze I use the most is based on a MC6G semi-matte base, which I altered with talc and calcium carb to make it more matte. At one point, I calculated out the unity formula, and it was well outside of the range that MC6G recommends. But I’ve been using it for going on 20 years, and it has been rock solid. Even in cases where a customer brought back some 10+ year old bowls, where the glossy liner glaze was visibly losing its shine. These customers are heavy dishwasher users, and again these pots had been in almost daily use for 10+ years, but the matte glaze on the outside was exactly like day 1. 

Unity formulas, flux ratios, boron charts are all useful guidelines, but glaze chemistry has far more variables than us mere humans can test. No substitute for first hand experience. “Melt and see” is still an indispensable mindset. 

[C.Banks]

13 hours ago, Min said:

I went through the Techno File topics from Ceramics Monthly and the only one that struck me might possibly be it is the "Ingredients' Roles"  article written by Steve Loucks in the Nov 2021 issue. It's behind a paywall but you can access 3 free articles a month.  Basically Loucks looks at glaze components and lists them in a specific sequence of spars, fluxes, clays and glass formers then looking at the fired glaze in relation to what the ingredients do and what influence they have on the glaze. Alterations are then made to the base glaze to see how the different components change the base. There is a brief comment on UMF but not much. Possibly what you were referring to?

It was definitely older than 2021. I worry now maybe it was from the Potters Quarterly from the UK. I'll find it but it'll be a few months before I get back there.

[Min]

2 hours ago, GEP said:

“Melt and see” is still an indispensable mindset. 

And then use the pots.

 

2 hours ago, GEP said:

where the glossy liner glaze was visibly losing its shine

High boron in this glaze? Large amount of Gerstley Borate?

[GEP]

3 hours ago, Min said:

High boron in this glaze? Large amount of Gerstley Borate?

Yes.

 

3 hours ago, Min said:

And then use the pots.

And if possible, let someone put them through a dishwasher 5x/week for 10 years! No formula can give you more information than that.

Edited January 10 by GEP

[PeterH]

6 hours ago, GEP said:

Unity formulas, flux ratios, boron charts are all useful guidelines, but glaze chemistry has far more variables than us mere humans can test. No substitute for first hand experience. “Melt and see” is still an indispensable mindset. 

Hard to argue with that, but I would suggest that they can help reduce the number of tests you need to make.

For glazes that phase-separate (e.g. many mattes) the UML formula will not accurately reflect the composition of the different phases.  Which raises issues of interpretation and limit setting.

[Min]

3 hours ago, PeterH said:

Hard to argue with that, but I would suggest that they can help reduce the number of tests you need to make.

For glazes that phase-separate (e.g. many mattes) the UML formula will not accurately reflect the composition of the different phases.  Which raises issues of interpretation and limit setting.

+1

Linda Arbuckle quote below regarding glaze calculation that I think pretty much sums it up for me:

"The purpose of glaze calculation is to determine the total amount of each element present in a glaze, and the proportions relative to each other. With that information at hand, it is possible to calculate materials substitutions, revise melting points, and do other useful calculations. In the end, testing is the final proof, but unity molecular formula gives you a more informed method of choosing what to test."

Are there qualifiers to interpreting the figures with glaze calc, yes of course there are. 

Glaze calc is another tool in the toolbox, one that can save a lot of work and material waste. I also use Limit / Target Charts, they aren't written in stone either but combined with UMF they can be a pretty good indicator if a glaze is worth mixing up and testing. An overload of boron, for example, might make a pretty and interactive glaze but I do question it's durability. Lots of lithium, I'm going to be wary of shivering. High level of sodium and / or potassium, odds of crazing are going to increase. Low alumina and / silica, glaze is not going to be durable regardless of flux ratio.  And so forth.  

Recently there have been a few materials that have become unavailable to potters, Custer, Gerstley Borate, some talcs plus the EPK shortage. Looking at the UMF for any of these offers a way to find alternative materials and or a combination of materials that can be used in place of ones lost and bypass a lot of the trial and error testing.

 

 

 

Edited January 11 by Min

[Kelly in AK]

7 hours ago, GEP said:

And if possible, let someone put them through a dishwasher 5x/week for 10 years! No formula can give you more information than that.

And here we come to it, the rub. 

Glazy has been a godsend to me, and I’ve yet to see anything bursting that bubble. I learned glaze chemistry and calculation thirty years ago in college, and used it loosely, only to evaluate recipes. Now, as then, I rely heavily on materials knowledge and gross ratios to come up with what I believe will work. Glazy allows me to put my guesses into a context of what has worked in other places for other people, and reduces (not eliminates) the testing. For materials that don’t have a published chemical analysis, or materials that have the same name but varying compositions (this talc vs. that talc, “ potash spar,” “boron frit,” or my local clay) there’s still guesswork. 

It takes much less effort to arrive at a data point that before would have been tedious to find, even with previous glaze calculation software. Glazy rests on the shoulders of everything that came before it and I don’t discount that, but we live in good times. Three cheers for Derek Au. 

I, like @Roberta12, look for that sweet spot on the UMF chart, nudge my glazes towards it and wait and see how the pots look after a few years in my kitchen. The only faster way to test seems to be alternating baths in strong alkali and acid (good old lye and that potent 30% vinegar @PeterH mentioned in another post). Like the weatherman, we haven’t arrived at perfect prediction, but it’s a lot better than it used to be. 

[Callie Beller Diesel]

I’m currently in an interesting position of having to revise most of the 10 shop  glazes at a new teaching studio that weren’t properly tested before large batches were made. The person who chose them quit, or he’d have been fired. The glazes were all chosen entirely by the numbers: they all fall within the Stull recommendations, and don’t have weird variances in UMF. Most of them have easily traced provenance and have good reputations.  But one failed an overnight vinegar test, and three more require weird bucket flocculation acrobatics that are deeply impractical to maintain in a teaching studio. One is pretty pricey because it’s half frit. 3 of them contain gerstley borate, with no attempt to reformulate. They were all mixed to the exact same specific gravity. 4 of them ran like a track star because of that. Only 2 out of the 10 need no immediate work. The person who put this glaze stable together read alllllll the technical manuals, but had zero practical experience. 

But I was also taught glaze chemistry (*points flashlight under chin*)  in the Before Times when there was No Digitalfire! (Woooooo!)  Kidding aside. We were subjected to line blending every material in a chosen base glaze just to see what happened.  My left eye still twitches thinking about that level of abject boredom, and I think the prof may have secretly hated us all. I remember thinking at the time that we were all probably reinventing the proverbial wheel, and that a reference text of some kind HAD to be out there somewhere to narrow things down. I am deeply, deeply grateful that glaze calc software exists to eliminates a lot of that kind of needless pedantry, and material waste. 

Ideally glaze calc and empirical testing should be used together. 

[C.Banks]

On 1/9/2024 at 10:59 AM, Min said:

during the cooling phase of the glaze

I was looking for the trial version of the NIST? phase diagram software and this: https://phasediagram.weebly.com/eutectics.html reminded me of some language here.

I don't pretend to understand it all although I do grasp the larger 'chunks' and descriptions of parts getting squeezed out and reforming encouarged me to wonder how many of the principles might apply to the glazes we find most appealing.

There was a discussion of overlays for the stull chart that gets stuck because the diagrams are copyrighted iirc.

[Min]

10 hours ago, C.Banks said:

I was looking for the trial version of the NIST? phase diagram software and this: https://phasediagram.weebly.com/eutectics.html reminded me of some language here.

I don't pretend to understand it all although I do grasp the larger 'chunks' and descriptions of parts getting squeezed out and reforming encouarged me to wonder how many of the principles might apply to the glazes we find most appealing.

There was a discussion of overlays for the stull chart that gets stuck because the diagrams are copyrighted iirc.

Well that's a nice little bit of light bedtime reading isn't it? 

Glad I'm not the only one thinking precipitates effect calculated flux ratios. Interesting seeing the phase diagram overlaid with Stull but found it hard to decipher.

[PeterH]

> I was looking for the trial version of the NIST? phase diagram software ...

Just to point out that there is a time-dimension to phase transforms that phase-diagrams don't capture.

A physicist might say that they are "thermodynamically correct", and only show what phase has the lowest energy under the given conditions. Saying nothing about how long the change of phase will take.

AFAIK it's rarely of practical significance, although I suppose it's relevant when the timing/temperature of the firing becomes important: e.g  slow-cooling microcrystalline glazes, nursing macro-crystalline glazes.

The effect is spectacularly evident  in  the phase diagram of carbon.

Normal temperature and pressure is about 1 bar & 300K. So every diamond you have seen is about 1,000 bar away from a point where it is "stable"  ... and not much closer during the geological time where it was in fairly-near-the-surface rocks.

PS
https://www.whiteflash.com/diamond-education/diamonds-how-do-they-form/

Edited January 12 by PeterH