Heat-Pt. 1-Cones
6.18.2009
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.
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.
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?