Heat-Pt. 1-Cones

I have been pondering what I want to do about the topic of temperature for a while. At first I thought about talking about specific temperatures (Cone 6, Cone 3). Then I realized that there is an elephant in the room. That is the very notion of heat. We take the concept of heat for granted, we declare temperature (04, 6, 10) and then sort of leave it there. But heat is a very complex and difficult subject, it is defined by history, functionality and ceramics science. With that in mind, today I start an ongoing series on the subject of heat.

To really talk about heat we need to talk about history, unfortunately I know that is not a very sexy subject to start off. So I'm going to start in the middle (not to worry, we'll talk about history next). So, where I want to start is Cones. We treat cones as gospel, yet, can anyone tell me why Cone 10 is cone 10? Or why Cone 10 is 2381F/1305C? Or do you know why there is the Cone 01/1 divide? Does anyone know why we have all the problems with cones? It all seems a little random doesn't it?

Well, it all goes back to color, before pyrometers and cones, the only way we had to monitor temperature. It is a great method, in fact some of the more accurate temperature measurement devices today are optical, monitoring the color of the furnace. Reading temperature by color is a relative (and dangerous) pursuit. So alternatives were sought.

Enter Herman Seger. Seger is a really important person in the history of ceramics, we was a German Ceramic Scientist who lived from 1839-1893. He was a prolific thinker and inventor. and published 170 papers, so many he started his own journal.

In 1886 Seger published "Pyrometer and the measurement of high temperatures with standard cones". If you are in Europe, cones today are Seger Cones (opposed to Orton in the States). In this paper, Seger laid out the entire foundation for the modern ceramic temperature (Along with glazes, but that is a whole other subject). What Seger had discovered what that there is a relationship between Chemistry and Temperature. In that, when we apply heat to materials their reaction is based on the amount of heat used, and the composition of the material.

I'm going to do something now that is going to piss a lot of you off. But it literally has to be done, there is no way around it. I am going to talk about the Unity Molecular Formula (Or Seger Formula). If you don't know about the UMF, unfortunately I am not going to explain it here (Maybe later, but not now). The reason I have to talk UMF is that it is the basis for Seger's work and cones to this day.

What Seger realized is that by incrementally increasing Silica and Alumina level, there was a increase in representative temperature. So to say. A cone with a composition of 1.0 Silica and 0.1 Alumina (0.3 R2O:0.7 R0) would soften and bend at "Cone 1" And a cone with a composition 2.0 Silica and 0.2 Alumina (0.3 R2O:0.7 R0) would melt at a higher temperature (Cone 2, who would have guessed it?) This system is constant.

So on and so forth. That is why when we look at a cone chart, the temperatures seem random. They are reflections of the temperatures at which chemical reactions happen, and not an arbitrary round number.

Notice one thing, If you know your UMF you will notice that they look exactly like Cone 10 UMF Glaze numbers. That is exactly right. What cones are, is glaze, in dry cone form. Cones are just glazes have aren't fully melted yet. The bending and softening is the begging stages of glaze melt.
Also, notice that I started with Cone 1. The fact is that Cone 1 is Cone 1 is because it was the limit of the chemistry and the materials. To get lower temperatures, an entire new system on top of this one, had to be developed.

I think that is enough for today. I hope everyone found this informative, if you have questions please ask in the comments, and tell your Friends and spread the post around.


Alex Solla said...

I think this may have been one of the epiphanies I was waiting for. Even after all my years of glaze geekdom, I have yet to read much of Seeger's work. While I certainly recognized his contributions, I hadn't really seen this laid out in such an elegant way.

Almost daily, on clayart I hear folks ask how to bump their maturation of the glaze up a cone or two or down a cone. This SHOULD help them to understand how to approach their testing process.

I guess my next question is how stability of glazes plays in to the relationships between temperatures. Ie, if a UMF ratio exists at 1:6:6.... and we increase this to read 1:5:6 I know empirically it will affect melting, but I can also surmise it will affect stability as well. Advice?

Matthew Katz said...

Hi Alex,
Glad to know that this helps! Spread the word around.
The basics of temperature are laid in the UMF and you basic theory is correct, about how to tweak a cone or two. But there are some other subtleties that come into play too. I will address that more thoroughly in a post to come, that is where I am heading with this whole thing.
Can you clarify your question? 1:6:6 (?) is that Flux:Al:Si ? If you can clear that up I can answer the question.

Alex Solla said...

I guess I think in UMF without clarifying... yes, for me the ratio always reads flux:al:si

So, explain away.

Funny thing about this aspect of UMF, was that Val Cushing didnt really delve into it. I learned most of what I know from watching Hyperglaze evolve and from testing ideas on countless glazes.

Reading Parmelee helped too.

Matthew Katz said...

Hi Alex
The question about stability/functionality does rely on UMF values. What we forget is that UMF values, do represent actual amounts of material in a glaze. So that High Al/Si UMF values, means more Al/Si in the glaze.
Also there is a relationship between the temperature of the glaze and the amount of Al/Si. Because, it takes more energy (Higher temperatures)to melt more Al/Si. So, the "stability" is based on those levels. Meaning a glaze with too little Al/Si (ie. a cone 6 glaze) fired to cone 10 will run. Because the excess energy of the hotter firing cannot just be displaced. So when all of the material is melted the system has no choice but to decrease in viscosity (hence running). Conversely, a glaze with too much Al/Si will not melt as there is not enough energy in the kiln to melt the mass od Si/Al, so it will be dry and under-fired.
I'll get into the subtleties of this in an upcoming post.

Matthew Katz said...

BTW check out the background on my twitter page. www.twitter.com/matt_davesclays
In the Porcelain for the People, you can see my fondness for Parmalee.
There is no doubt that UMF is a bear of a system, but the more that Carty and I have researched, we have found that it is literally THE only was to look at glazes. And the use of it in cones should convince everyone of the validity of that idea.

Stephani Stephenson said...

Thank you Matt. I did not know about the cone # relating to the numerical SI: AL composition.
light bulb going ON here!

Anonymous said...

Dear Matthew,
The ratio of Aluminium Oxide to Silicon Dioxide is constant. It does not govern the deformation temperatue of pyrometric cones.
The governing factor is the ratio of R2O oxides (0.7K2O and 0.3Na2O) which reduces by 1/10 with each incremental addition of [(1)Al3O2/(10)SiO2]
Composition for Seger Cones from 022 to 12 can be found in Deboos,Harrison and Smith, Handbook for Australian Potters. IBN0-454-00448-6
Best regards,
Ivor Lewis

May Luk Ceramics said...

Please write more historical background if it is required. History is not boring. Learning is never boring. Not being curious is boring.

Anonymous said...

Sorry Matthew,
Mental arithmetic was never one of my strong points. Jumped to the wrong conclusion.
A better way of expressing the relationship of the fluxing agents to the refractory agents is that as you move up the list from 1 to 12 the quantity of flux is inversely proportional to the quantity of refractories.
In other words, as maturity level is increased diminishing quantities of flux are required to achieve an equal temperature rise.
Best regards,

Matthew Katz said...

Hi Ivor
Your interpritation of how the system works is correct. We are both discribing the same thing in different ways.
That said, We do not express flux /glass former in the way you describe. This is because to effectivly analyze the complexaties of the relationsiphs we require something to judge scale. By normalizing to the fluxes we are provided with an interprative scale.

Alex Solla said...

Hey there Matt-
Question along this same line...
if one were to take a glaze currently working well at c5, and wanted to increase the glaze's maturation temp to c6 for the sake of the claybody (and having just simply pushed the glaze to c6 with no mods it looks awful!)....

would I simply increase the ratio
by 1:.1:1? (flux:Al:Si)
Ie, if the UMF looks like: 1:.631:3.57

Would altering that to 1:.731:4.57 bring the maturation temp up a solid cone?

Am I understanding Seger's process?

Eleanora Eden said...

When I was firing some loads at ^1 I was quite confused by the ^01/^1 situation. I queried the Orton company without response. Looking forward to your comments on that.

This a very welcome topic.

Eleanora Eden

Matthew Katz said...

Hi Eleanora
The O1 Transition came when people realized that Lower temperatures were needed, yet the existing chemistry could not function in the existing model.
A system was eventually created using Iron as a flux that was able to achieve those temperatures. I don't not know for sure, but the 01, 02 naming methodology, I suspect was just the method that seemed logical for moving below the established 1,2,3 system that had been created.