[Clayart] Pyrometers and kiln charts

[RICHARD MAHAFFEY]

As Mel and David stated a pyrometer is useful for determining if a kiln's temperature is going up or down or holding and for comparing one firing to the next.  The Thermocouples we typically use are not high enough quality to use solely in a firing without some varying risk.  Cones are better for us as Orton tests the batches of cones frequently to assure that they are accurate at measuring heat work.

In Japan Potters that I know have much more expensive and much higher quality pyrometers and thermocouples.  They often use them with a known schedule to determine when a firing is done.  They also chart the firing recording all of the data such as time, gas pressure, air setting - (often forced air burners have air flaps to control the amount of air going into the fan or a speed control on the fan motor) ,damper setting and the weather.  They also graph the firing which makes it very easy to spot a change in the firing right away by comparing previous firings.

At San Jose State in the Dim Past we both had the data recorded and the graph of the firing on our firing charts.  That could be because Dr. Herbert Sanders did a Fulbright in Japan (His book the World of Japanese Ceramics came from that time) or because that was the way it was done in the 30's and 40's.

I recommend that you graph your firings and you can compare the curves one firing from the next at a glance.  Recording the data faithfully is important.  That information can let you know when your firings are trending in a way that you don't want or to show you a trend that you want to follow and explore.  

For the 20 years that I had one particular kiln I kept every firing chart and once in a while I needed to see how the current firing compared to some previous firing. I was able to look up the information instead of wondering what was different or the same in the current firing.  I also used those charts to let my wife know when I might be home if a firing was running long.

At school I use the charts to spot a time when I might need to look into why the kiln firing was going longer and point me toward possible maintenance that would need to be done.

As David said there is no substitute for an engaged mind paying attention to a firing - but taking notes helps (particularly in a wood firing that is several days long and when you are getting tired) is very helpful too.

YMMV,
Rick  
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