Stull Charts Matte Glazes and Total Oxygen Ratio

[High Bridge Pottery]

So I didn't want to completely derail bees and stones topic and go way off on a tangent but I found myself wondering what Stull had to say about his chart and any insight into matte glazes he had. After finding his research a very interesting read I wanted to share it here.

Who knew there was a Chart 2 to his research  

If anybody can help me understand what total oxygen ratios are that would be great. I am guessing it is the ratio of oxygen to everything else but how do you work that out? Still lost in what a true matte glaze is. It seems to be crystals in a glassy matrix but when does that go to far to be unusable or no longer classified as a true matte. What if all the crystals are on the surface? There's probably no right answer.

 

1 hour ago, Bill Kielb said:

Yes lots of generalities around clay often don’t always hold up in all cases but being extra careful not a bad thing I suppose. Stull drew his map and did his research prox.. 1912 so maybe he indirectly inspired Currie. RT Stull was the head of the ceramics engineering department at the University of Illinois - my home state.

 

It does seem like Stull was blending long before Currie as he says "The glazes in that portion of the field covered by the A to H series were made by blending the four extremes according to their combining weights."

Credit to Glazy for these images - https://wiki.glazy.org/t/influences-of-variable-silica-and-alumina-on-porcelain-glazes/index.html

I have rotated chart 2 and will attach at the end for easier viewing.

 

[Bill Kielb]

Yep, Stull! He was limited by available fluxes and his claybody at cone 11. The most useful for me is his matte / gloss line and with some indication of how it ought to fire which then prompts further diagnosis such as is this fully melted, etc…. We get the question of how to make a matte glaze here every so often.  Slow cooling, magnesium matte are the typical responses and they are fine, but moving something between matte and gloss generally follows Stulls trend which is fairly easy.

I have designed visually as well and Stull folks often group. I do like the simple true matte definition though and have observed the over fired runny matte as well as added silica from matte to full gloss.

Sue M has some nice in studio testing and research detailing how to get better clarity etc….

Derek Au (Glazy) I believe is trying to gather data for a heat map to apply to the Stull chart. I am partial to Flux ratio as being an initial indicator if a glaze likely can be durable. The Katz research on boron required I find very useful as well.

Cullen W Parmelee also interesting work - (Stull Era), lots more for sure not to be forgotten.

[High Bridge Pottery]

I have managed to find Transactions of the American Ceramic Society vol 2 through 19 so got a lot of reading to do. I haven't been able to locate Professor Binns article in volume 7 which seems to be looking into matte glazes too which is talked about in the comment/discussions. I want to try and figure out why they are interested in the oxygen ratios.

 

Edit: I managed to find C. F. Binns article in volume 5 after looking in the collective index  Strange that the files don't total 1000kb but it seems to stop me putting them all in one post. Will continue in another post.

 

 

Edited February 12, 2023 by High Bridge Pottery

[High Bridge Pottery]

[High Bridge Pottery]

After a bit more digging I have found the actual paper they are talking about in stull's discussion. It just isn't listed anywhere besides a page number with no volume so it was in volume 7 after all.

 

[High Bridge Pottery]

A bit more searching and I have found how they are calculating the oxygen ratio. Orton seems to say it is only useful in comparing similar glazes and they all seem unsure if you need to include B203.

 

I have no idea  what to do with it yet.

[Bill Kielb]

interesting in the end Stull seems to have reasonably simplified all this to regions in his map and a matte  / gloss line based on si:Al 

[Min]

Thanks for finding those equations Joel. I'm wondering if its just adding another variable and / or a different equation that is muddling the difference between  the SiO2:Al2O3 ratio insofar as looking at those levels (in addition to having the flux ratio of 0.3 R2O:0.7 RO) to determine with math whether a glaze will be an alumina matte, gloss or somewhere in between without looking at slow cooling glazes and or different flux ratios that employ more than the one mechanism to get a matte.  

 

[High Bridge Pottery]

As far as I can tell it is an extended Si:Al ratio showing the relationship of acid (silica) to base (RO and Al2O3). There is a lot of discussion on if you should have B2O3 as an acid or a base and some interesting experiments showing that you can trade Al2O3 for B2O3 as they are both sesquioxides (an oxide in which oxygen is present in the ratio of three atoms to two of another element)

Some argue that if B2O3 was an acid you should be able to reduce silica when adding boron but most times you need to increase silica when adding boron so how can it be seen as the same as SiO2. 

 

If anybody wants to get copies of the Transactions of the American Ceramic Society volumes you can find them here - https://archive.org/search?query=subject:"American Ceramic Society" All in the public domain so I assume I am fine sharing here as it's not for commercial use. 

 

Edited February 12, 2023 by High Bridge Pottery

[Min]

But we already know boron is a glass former though. 

[High Bridge Pottery]

I think it seems to be a glass former, intermediate oxide and flux all depending on chemistry. I would maybe argue that in pottery we are using it more like a flux than a glass former due to its reactions with silica but it seems to be pretty versatile in its use. One comment that got me from the NCECA talk "Glazes without borders" from Peter Berg was that low fire glazes higher in boron were more durable and resistant to attack than high fire glazes with little or none so it seems to be fluxing while also acting like alumina by increasing durability and resistance. 

There's an interesting comment on the B2O3 page on digital fire that it can even be refractory. "B2O3 can actually be a refractory, frits with very high contents are used in the refractory industry. These frits do not contain SiO2 (depriving boron of a reaction with it to form a borosilicate glass)."