Paul sits back down and gets last remaining instructor, Lisa Orr, along with Chris McClellan, aka Uncle Mud, to go more into their Rocket Kiln stuff.
The latest rocket kiln is the fifth prototype in the series, with the first being built by Ernie Wisner and was somewhat dear to Paul as a sort of “not so great” version to try and keep people from re-inventing the Mk.1 mistakes (although it’s removal didn’t seem to invite much failure in the latest version). While Lisa and Rodney Morgan were making stoves for the Free Heat Movie, Rodney was fiddling with the chimney (technically called tuning the riser), Lisa used a pyrometer to measure the effects of his tuning on the kiln’s temperature. She also used little glazed “cones” to measure both the overall temperature and the distribution of any hot or cold spots in the kiln by checking to see which glazes had melted after firing them.
The kiln built during the Rocket Mass HeaterJamboree got to a gas temperature of about 2200 degrees according to the pyrometer, whereas the cones (which measure the temperature that pottery will get to) recorded closer to 2000 degrees. The delicate blue glaze they put in as a test even got fired properly with no reduction or discolouration, outside of the one they put at the bottom of the J-tube.
The PTJ rocket kiln has been built around a full-size 8-inch J-tube rather than the smaller tubes used by prior prototypes to try and make it less of an iterative prototype and maybe stick around longer. Yes, this will increase wood consumption, but it’s still an order of magnitude or two less than the amount used by Lisa’s old job that took several trailers full per firing, to say nothing about how much less hassle it is to not have to notify the fire department and rest of the postcode every time it’s lit.
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