First Mugs: the Good, the Bad, and the Ugly

Overall, I think I'm pretty happy with the way the ash glaze turned out (particularly the dark green one).  One glaze turned out a dark green-to-black, and the other was an opaque gray that I'm not crazy about.  In some places, for reasons I don't understand, the glaze had beautiful blue and white streaks in it.  This seemed to happen more where the cups received the most fly ash from the firing.

About half of the mugs that I made from the iron-bearing clay body warped excessively or split during the firing.  Some split, and then were healed again by the melting glaze.  Others, not so fortunate.  

I think in the future I'll be doctoring the clay body a bit with other materials to help it handle the firing better.  

Here are some of the results:

Kiln Firing Log

I just recently acquired a pyrometer and used it in its first glaze firing.  It was really helpful to have more real-time information to work with than just the pyrometric cones that I've been using.  

When I fired the kiln this last time, I periodically recorded the temperature as measured by my pyrometer.  Because the pyrometer doesn't extend as far into the kiln as it is supposed to, I think that the temperature measured by the pyrometer is approximately 100 degrees celsius cooler than the actual temperature, which I measure using pyrometric cones (at least from about 800 degrees Celsius and up). 

I fired the kiln from 5:15 or so a.m. until around 11:00 p.m. or so, and the pyrometer reached a maximum temperature reading of 1,100 degrees Celsius. 

The first three hours of holding it at 200 degrees Celsius was intentional to burn off the water in the clay slowly to avoid explosions.  From 200 degrees up to 600, the rate of increase was fast - about one degree Celsius per minute.  From 800 to 1000, rate of increase was slower, but still steady, and the last bit from 1000 to 1100 was painful.  As I write this, the kiln is still too hot to unload.  It is the first high temperature glaze firing with actual pots in it, not just test tiles. 

I can't stand the suspense.