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

[C.Banks]

13 hours ago, Min said:

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.

 

The folks who can interpret comlpicated ideas and express themselves in approachable language sure help the rest of us follow along.

[PeterH]

On 1/12/2024 at 12:34 AM, Min said:

Glad I'm not the only one thinking precipitates effect calculated flux ratios.

Have you tried to measure/estimate the UMF of the glaze matrix rather than that of the matrix+crystals? It seems a more logical number to use with the Skull chart.

For a high-calcium matt I understand that the crystals are calcium silicate, there are several to choose from but I'll assume 2CaO·SiO₂.

So do a line blend of your existing glaze recipe and one with rather less 2CaO·SiO₂ (or its precursors).

If you've straddled the just-no-precipitate recipe you have a good estimate of the matrix chemistry. If you didn't remove enough 2CaO·SiO₂ you still have a closer bound on the matrix chemistry, and an idea how big the change in parameters such as flux-ratio are likely to be.

PS

- Obviously stick to a single cooling cycle.

- Probably best done converting the UMF to a  "recipe" of oxides. Subtracting some 2CaO·SiO₂ from the recipe. Then re-normalising (i.e. calculate the UMF of the new recipe).

- No need even to consider if/how you can make up that recipe from your original list of ingredients.

 

Edited January 13 by PeterH

[Min]

@PeterH, using your train of thought...

If a high calcium matte glaze recipe was put into the EU calculator then the calcium in the recipe reduced until the EU calculator showed no excess calcium then in theory it would be a gloss when slow cooled. I'll try plunking MC6G  High Calcium Semi-matte one into the EU calc. and see what happens to the flux ratio. I'll try it with both wollastonite and another recipe with CaCO3 and see where the flux ratio lands. (might be tomorrow before I get to it)

 

[PeterH]

8 minutes ago, Min said:

@PeterH, using your train of thought...

If a high calcium matte glaze recipe was put into the EU calculator then the calcium in the recipe reduced until the EU calculator showed no excess calcium then in theory it would be a gloss when slow cooled. I'll try plunking MC6G  High Calcium Semi-matte one into the EU calc. and see what happens to the flux ratio. I'll try it with both wollastonite and another recipe with CaCO3 and see where the flux ratio lands. (might be tomorrow before I get to it)

 

I assume that you intend to reduce both calcium & silicon, or is the amount of silicon involved a negligible fraction of that in the glaze..

I'd wondered if there was a trustworthy limit formula you could use, be interesting to see what it says.

Edited January 13 by PeterH

[Min]

4 minutes ago, PeterH said:

I assume that you intend to reduce both calcium & silicon, or is the amount of silicon involved a negligible fraction of that in the glaze..

I'd wondered if there was a trustworthy limit formula you could use, be interesting to see what it says.

I'll plunk it in and see what it shows. If the EU calc shows excess silica (like I assume it would) then yes. 

edit: I'll use this recipe to play around with. (without any colourants)

Edited January 13 by Min

[Min]

When I enter the MC6G High Calcium Matte 2 into the EU calculator I'm not seeing excess to the eutectics of CaO even though this is coming in at 0.90 in the UMF.  I'm going to assume this glaze uses a different matting mechanism, perhaps the excess alumina and silica causing the matting or a micro rippled surface. If that's the case we need another recipe to test the theory with or reduce the silica and alumina perhaps. 

 

[Bill Kielb]

Might be interested in some of the discussion here @timthrontonceramics has an interesting comment Re: this composition. Comment here: https://glazy.org/recipes/55141.

0.1:0.9 definitely not something I would design to and far enough from my 0.2:0.8 awareness radar that would subject this to testing for sure. .23 boron, not overly crazy either for that matter. I did pick this version of the original above because it is the famous high calcium clear with the most obvious departure from the original recipe above - less alumina

All interesting stuff for sure. 

Edited January 14 by Bill Kielb

[C.Banks]

On 1/13/2024 at 12:59 PM, Min said:

When I enter the MC6G High Calcium Matte 2 into the EU calculator I'm not seeing excess to the eutectics of CaO even though this is coming in at 0.90 in the UMF.  I'm going to assume this glaze uses a different matting mechanism, perhaps the excess alumina and silica causing the matting or a micro rippled surface. If that's the case we need another recipe to test the theory with or reduce the silica and alumina perhaps. 

 

I have a project that leads me to believe Al2O3 amounts over around 0.3 restrict the development of micro crystals.  I know this is off topic and specific to do with magnesia mattes too so may not be too useful here. These mattes do respond to calcium though - or as much as I'm certain I remember a line blend proving + calcium = + matte in  magnesia mattes.

I'm unsure this helps understand the Eucal results at all. This conversation only reminded me of a glaze project I'm somewhat familiar with.

*to add here - additions of calcium seem to reduce the claculated Al2O3

Edited January 21 by C.Banks