For my third soda firing, I wanted to re-test all the clay bodies I had made for my second firing in a different atmosphere. I had seen what they looked like in a lightly reduced atmosphere, but was curious what would happen if I again ignored body reduction but reduced the kiln hard during the soda introduction.
I also took the opportunity to try and hone in on some of the successful clay tests by making some more. I mixed up 7 more stoneware clays (50lbs each) and 5 more porcelain test bodies (10lbs each). I threw these into the same shapes as my original tests: trimmed bowls and cups. I had a few orders to fill so I hoped for the best and made them out of these untested bodies too. I also threw a few flower pots to help fill up the kiln.
For this firing I pre-mixed my soda using Gail Nichols’ recipe. 50% whiting, 25% light soda ash and 25% baking soda (15lbs soda : 15lbs whiting). Supposedly the whiting helps separate the soda particles so they can vaporise more effectively. I had to take dense soda ash and heat it to 600°F in an electric kiln to convert it to light soda ash. I mixed the dry ingredients first and then added water. As I mixed the solution with an electric drill it started to turn slushy and then solid at a certain point. It was very much like making plaster. I spooned this mixture out into egg cartons as you can see below. Mixing the soda this way was super easy. It took much less time to introduce than spraying.
I would chuck in half an egg box in each side along with several pieces of wood, and then pushed the damper in to 3". I also turned the air and gas down a little during this soda period. I took my time with the soda introduction, starting at cone 7 and continuing up to cone 10/11. After introducing the soda and wood, I kept the kiln in pretty heavy reduction for half an hour (during which time the temperature crashed about 150 degrees) and then I opened the damper back up to 6” to regain the temp for half an hour. So these cycles were an hour long (5/6 hours of soda all together). I think I could maybe cut this down but it made it easy to manage, coming out every half hour to adjust the kiln.
Here are some pictures from the unload…
RESULTS
I sort of hoped that with this firing, I would get all the answers. That was not the case! I came away with more questions than answers… again. But I guess that’s why it’s so fascinating.
I packed the kiln tighter than my second firing (old habits die hard) and this made for some dry areas.
The top and bottom of the kiln got lots of soda, but the middle was pretty dry. To remedy this next time, I plan to pack the top and bottom tighter and leave the middle more open. Also just cramming less pots in.
The heavy reduction during the soda introduction made for quite a bit of carbon trapping… mostly up in the top of the kiln. There were lots of darker greys up there whereas down low, it was a lighter soda build up. Down low, I got more grey/black specks on a white surface rather than up high, where it was lighter grey spots on a darker grey surface.
I found the darker heavily carbon-trapped surfaces from the top of the kiln to be a bit too contrasty with the orange flashing. I don’t think I want to reduce this heavy during soda introduction going forward.
Here are some of the pots I found most interesting from my first couple of firings…
I organised the tests and put them to bed until I get back from the holiday break. Excited to get stuck in to my fourth soda firing in January of February. But for now, it’s time to read some books and relax!
Hope you all have a lovely holiday and here’s to a better 2021!