[Hermes]

In the previous post I treated the plotting of Fluxes, Amphoteric and Glass formers as a help and as an item to document ones work.

With a little exaggeration, I can put that there are as many limit formula as there are authors on the subject. I stick to those mentioned by J. Hesselberth and R. Roy in their book "Mastering Cone Glazes". This range of limits is also available in the INSIGHT and other glaze calculation software.

What is the use of these 'limit formulas'? As J.H. & R.R. put it: they are useful as guidelines, to make 'stable' glazes with the remark that one can make stable, good glazes who are way out of the limit formula.

My definition of a 'stable' glaze is a glaze that:

• Has no glaze flaws like: crazing, shivering, crawling or dunting
• Is food safe when required

Limit formulas can help but are not the universal panacea.

Herewith the J.H. & R.R. Limit Formulas. They give the range of moles in the unity formula for the different oxides:

Oxide range (Seger Unity) J.H & R.R.

K+Na2O 0.1 - 0.3
CaO 0.2 - 0.6
MgO 0 - 0.3
BaO 0 - 0.4 (Cooper & Royle)
ZnO 0 - 0.2
SrO 0 - 0.2
Al2O3 0.25 - 0.5
B2O3 0 - 0.3
SiO2 2.5 - 4.0

What you need is just the transformation of your recipe into the Seger unit formula. In glaze calculations software the limits are given next to it.
So you don't need to make graphs, but I do. Graphs are more meaningful to me than just figures. It is a personal preference.
In the example at the end of the text, SiO2 is divided by 10 to keep the graph in good proportions. The red marker lines show the limits.
The glazes MC6G 1 and MC6G 2 are way out of limits for CaO and below limits for the alkalis. These are nevertheless reputed stable glazes. One can here also conclude they are Alkaline Earth matts.

I document all my work with the topics mentioned in these posts, past, present and future.

I repeat: For information on glaze chemistry, visit my website at:
http://users.telenet...ics%20menu.html

Next time I will discuss briefly thermal expansion and its role in glaze flaws.

[Marcia Selsor]

It is very interesting that you come from a chemist' background. John Hesselberth also comes from that background. I really appreciate your chart.
I come from a visual artist background and charts really make sense to me. I had several glaze calculation classes back when we used slide rules. (dating myself??) I have old hand drawn charts of the ratios.
I hope others who don't have the background will read what you are posting. It is a valuable resource.

Thanks so much.


Marcia

[Hermes]

Marcia Selsor, on 12 January 2013 - 01:19 PM, said:

It is very interesting that you come from a chemist' background. John Hesselberth also comes from that background. I really appreciate your chart.
I come from a visual artist background and charts really make sense to me. I had several glaze calculation classes back when we used slide rules. (dating myself??) I have old hand drawn charts of the ratios.
I hope others who don't have the background will read what you are posting. It is a valuable resource.

Thanks so much.


Marcia

Thank you for your interest. I hesitate long before doing this. Our fellow member DocWeathers encouraged me to do so and he reviews part of my posts. My thanks go to him as well.

Hermes

[smastca]

Hermes - thank you again. The graphs make perfect sense to me. Again, I appreciate your postings - I look forward to reading more.
Susan

[yedrow]

I'm really eating this stuff up Hermes. Thanks again!

I'm curious, the KNaO on the chart is separate. Is the KNaO limit different from the separate KO and NaO limits? I kinda new to this so you'll have to excuse any silly questions on my part.

Joel.

[Marcia Selsor]

yedrow, on 12 January 2013 - 07:06 PM, said:

I'm really eating this stuff up Hermes. Thanks again!

I'm curious, the KNaO on the chart is separate. Is the KNaO limit different from the separate KO and NaO limits? I kinda new to this so you'll have to excuse any silly questions on my part.

Joel.

KNaO is a generic term for K and Na bases. Soda and Potash effect glaze colorants differently


Marcia

[yedrow]

Thank you Marcia!

Joel.

[Hermes]

yedrow, on 13 January 2013 - 02:06 AM, said:

I'm really eating this stuff up Hermes. Thanks again!

I'm curious, the KNaO on the chart is separate. Is the KNaO limit different from the separate KO and NaO limits? I kinda new to this so you'll have to excuse any silly questions on my part.

Joel.

Hi. Marcia answered and, I agree it might be confusing. I often thought to change that in my graphs when I was filling a record. But, for me also K an Na are behaving different so I leave it like it is. The trouble may be that Na OR K may get out of limit individually but when you sum up KNaO appears to be OK.

Thanks for your interest,

Hermes

[yedrow]

Thanks Hermes. I was wondering about that. I know I calculate them together on Insight, and on the graph they have the same limit lines. I was guessing that these were separate and the same. Thanks to Marcia, and to your follow up, I know why they were separated.

Joel.