Economic Historians and Kiln Design: Another just so ho hum story

Sometimes I wish academics would take the time to know what they were talking about before they attempted to cram a real world example into a predetermined paradigm.  Case in point Robert C. Allen,” The British industrial revolution a global perspective.

Pottery, for instance, was manufactured in both England and China. The design of the kilns differed greatly, however. English kilns were cheap to build but very fuel inefficient; much of the energy from the burning fuel was lost through the vent hole on the top (Figure 4). The typical Chinese kiln, on the other hand, was more expensive to construct and, indeed, required more labour to operate. Figure 5 shows how heat was drawn into the chamber on the left and then forced out a hole at floor level into a second chamber. The process continued through many chambers until the air, by then denuded of most of its heat, finally exited up a chimney. In England, it was not worth spending a lot of money to build a thermally efficient kiln since energy was so cheap. In China, however, where energy was expensive, it was cost effective to build thermally efficient kilns. The technologies that were used reflected the relative prices of capital, labour, and energy. Since it was costly to invent technology, invention also responded to the same incentives.

I call bullsheet! As someone who built kilns and fired them for years and who has intimate knowledge of kiln design history I must concur that this is yet another just so story by another just so economic “historian”.

It is true that downdraught kilns are more efficient than updraught kilns for the reason already cited in the excerpt. In the simple updraught (that is where the flame enters in at the floor of kiln and exits at the top) less heat work is done,i.e., the actual heat that gets transferred to the ware (think about the difference between horse power and torque). In the downdraught design heat is once again introduced at the floor of the kiln and then directed up the side walls into the arch where it is sent back down into holes at the bottom of the kiln and travels out through a flu exit on the floor. Here much more heat work is done so it is more efficient regardless of how many chambers there are.

The Chinese kiln is essentially a series of downdraught kilns strung together which are staggered along a hill. This is a clever innovation because it eliminates the need for a tall chimney which is necessary for most down draught designs. Now the Chinese Climbing kiln as it is known is special not only because it eliminates the need for a tall chimney but also because each ware chamber can be individually stoked. So the way it works is this. Say you have a ten chamber hill climbing kiln. You fire chamber one to temperature aprx 1315 degrees centigrade and then you fire the next to temperature and so on. Yes fuel is conserved because one is using the exhaust from the preceding chamber to pre heat the next chamber. So on the face of it the story holds.

But there are four other issues which the author fails to mention.

Significantly not all Chinese climbing kilns were of the multi-chamber variety some were single chamber climbing kilns similar to the Japanese Anagama (in fact the Japanese Anagama is a derivative of the Chinese). And while technically a downdraught it is really a cross-draught (the exhaust flue is slightly higher than the inlet). So not all kilns were of the multi chamber energy scavenging variety in Asia!

The second significant issue is temperature. Asians were firing their kilns to cone 10 (stoneware 1315 and higher for porcelains). Stoneware starts in the 1400s BC in China and began in Europe during the 1700s and 1800s as the Europeans sought to emulate the wares they were importing. But the point is this, achieving stoneware temperatures is difficult, costly and thus inefficient. It is a complex story but the difference between 1100 degrees centigrade and 1300 is not trivial and requires a lot of extra fuel. For example if you fire a modern IFB brick kiln of 20 cubic feet to 1300 you need between 2-4 extra hours of firing time @ a min of 1 million BTUs per hour. Now imagine the extra energy needed if wood is your fuel, your bricks are of the dense non-insulating refractory type, and your kiln is 10 chambers X 40 cubic feet. And this was the design of the Chinese kiln in question! Hardly an energy efficient model of production. All of which suggests fuel costs were not a significant factor or at least not a manipulatable factor.

The next issue is timing. Once the Europeans figured out how to find, refine and manufacture both the clay for porcelains and stoneware and the bricks for the kilns they almost immediately started developing downdraught two to three chamber kilns. In 1873 Mr Minto would actually take out a paten on his Minton Oven design: A downdraught two chamber kiln where the second chamber was used to pre-fire wares (bisque). However, in Germany they were already by 1858 using continuous firing kilns for bricks and this type of kiln is considered to be the basis of all modern industrial type kilns.

All of which brings me to the third issue: SCALE. Once you take into account the different types of fuels and the temperature at which the wares are being fired the issue that seems most relevant is economies of scale and specialization. The Chinese, Korean and Japanese, multi chamber climbing kilns made sense because pottery was made at the scale of the village. That is, whole villages were dedicated to the making of pottery. Such a scale required large multi-chamber kilns capable of producing large volumes of wares. This is why, I think we see an approximation of the Chinese kiln in the German continuous firing brick kiln: because brick construction was ubiquitous in Germany and the demand was huge such that kiln design was and still is dictated by the volume of demand rather than the relative scarcity of inputs.

Updraught industrial scale kilns are *more* expensive to build, not nearly as reliable, and the quality of the firing is poor (the difference in temperature between the top and bottom on a small kiln can be 100 degree centigrade!  Once large volume, high temperatures  and consistent results are required we see the Europeans switching over to down draft multiple or continuous chamber kilns.  Relative factor endowments do not play much if any of a role.

I suppose if I had Ricardo in the back of my head I would have reached the same conclusion as Mr. Allen.  Fortunately there is more between heaven and earth.


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