Firing Log

I have received some surprise when I mention that my floor sand melts during firings.  It really does, but it will only become glassy where it is thin enough to spread out on something harder, like the bricks I pointed out in my previous post.  Where the sand is thick, only the top layer will melt.

Here is an example from the sixth firing, one of the most beautiful firings and the most disastrous due to multi-level shelf collapsing.

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This piece was just back of the firebox — a band of black koge can be seen in the front of the image.  The rest of the images from the sixth firing are posted on this site, but the location is pretty buried — I should add them to the photogallery.

Anyway, Furutani’s kiln design has no trouble melting sand.  In fact, it is beginning to dawn on me that I will have to work harder to keep firing temperatures down a bit, as I believe I’ve been overfiring to some degree.

I think the 11th firing worked out quite well.  I outlined my firing plan earlier this week, and now, some of the results are available in the photogallery.

It was a very hot firing — cone 11 laid flat front to back (I don’t have any higher cones).  However, I think getting it so hot is detrimental in that the glaze tends to run completely off vertical pieces.  There are two problems with this — first, the glaze is gone, and second, foot grinding is a huge chore.  Perhaps in future firings I will work on controlling the maximum temperature to no more than cone 11.

What was most excellent however, is that I avoided the gray-gunk I mentioned previously by not overstoking.  I figure that when overstoking, I probably have a lot of gritty unburned wood particles flying through the kiln.  With optimal stoking, I still got blackening on the front sides, but the carbon creates an inky black glaze rather than 30 grit sandpaper.  I’m completely OK with inky black glaze — it looks neat.

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I also finally managed to mimic the surface of the floor bricks on a piece, specifically, the blue marbled glaze that forms where the floor sand melts onto the bricks.  The sand itself is inexpensive white sand that I buy at Home Depot — last time it was around $5 for 100 pounds.  The result is beautiful and the piece below is one piece I feel completely happy about.  It makes me want to get a bright light and a magnifying glass and mentally tramp through the mountainous landscape.

First, inspirational bricks:

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A snow capped mountain range:

   Photogallery on this piece.

I also experimented with some local clay I was given a while back by a friend doing some construction work around his house.  The clay he gave me is everywhere around here, except it’s usually 4-6 feet down so getting it is difficult.  It is a blue-gray color in its natural state.  When I made some test pieces with it (full report here), the 100% “dug-up” clay melted into a beautiful glaze.  For this firing, I decided to try lining some of my pots with this clay.  The results were interesting.

First, the failed cup:

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Same clay used as a liner glaze:

   View more images here (pics 7-9) and here (pics 10-18).

Finally, I’m also very happy with my new kiln monitor setup.  I had been using the software that came with my Radio Shack Digital Mulitmeters.  It was lousy software.  Recently, QtDMM has been released for Linux and OS X.  I put together a system with an old Mini-ITX board powered by an aging VIA Nehemia 1ghz processor (think 5-6 years old).  I used Ubuntu 8.0.4 for the OS.

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The added processing power over my old system (it died between the this firing and last year’s) allowed me to set up a chimney cam — basically just an old DV camcorder connected to a firewire port.  I used Kino to display the feed.  This helped save my knees.  What I used to do is go up the steps to the mid-level, and peek at the chimney tip through a gap in the roofs covering the kiln — when I saw the flames die out, I’d run down and stoke.  Well, my knees are getting beat up by running up and down the stairs during these firings.  Now I can just stand by the kiln and watch the chimney cam.

This is what I used to see:

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This is what I see now:

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When all is said and done, I’m totally satisfied with this firing.

PS:  if you’ve made it all the way down to the end, enjoy a sunrise:

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