First, it’s time to gather some notes for the future. Lessons learned from the pit fire:
- Make sure all work is bone dry before going into the pit fire. The second firing confirmed that pit firing (at least the way that I do it) can’t tolerate wet pieces. If the piece is made out of the Raku WC548 clay, it tears itself apart as the piece gets hotter. The EM100 does a better job of surviving, but with some cracking. When pieces are bone dry, they are surprisingly likely to survive.
- Heat slowly. This hasn’t shown to be quite as critical as I first thought – some of the pieces that were up against the fire first were also the ones that didn’t crack. I’d placed the wet pieces farther away from the starting fire, but not enough to dry them out.
- Cool slowly. This is the slowest segment of the firing process. I can’t confirm whether a quick cooling is causing any damage, but I suspect a few of the finer cracks are the result of me pushing pieces around too soon.
- Stack carefully. Position things with the understanding that the wood will shift and settle on top. It’s also good to try and put things only a little bit in the fire pit’s base layer of ash – they almost always turn out white to peach in color, and not the darker gray to black that I’ve been trying to get. Plus, I had 3 bowls break just from transport. Should have turned those in to slip instead of trying to fire them, come to think of it…
- Pretty much all colors go away. There’s no special point to this one – I just haven’t figured out how to get non-glaze colors to stick on the clay and survive the firing. I’ve tried mixing ink with slip and painting it on the surface (which turns pure white after firing, apparently), and smoking with coffee (burnt away) and copper (distorted pennies, no effect). The Raku clay develops some peach and pink, but across the whole clay body. There’s some curious reds and blacks that have formed on the surfaces, but I can’t quite figure out where they’re coming from. Seems to be leave-behinds from the person using the fire pit before me.
The fire seems to get to 950C (1700F) or lower. Some portions of the clay visible through the coals were glowing a healthy dull orange. If my eyes are right, that’s a pretty warm temperature. Still a little lower than it should be for the amount of time these pieces are sitting in the heat, but it’s a good thing to work with. I’ll see how I can keep the fire going longer at that heat. Wood just disappears so darn quickly when the fire pit is that warm.
Heated these up a little quicker at the start, and didn’t leave time for all the pieces to get to bone-dry before I threw them in the fire. Looks like the Raku clay is less forgiving than the plastic clay when it’s wet, and largely broke more than survived.
Now some Research…
Glass melts at way too high of a temperature for me to make use of it. Somewhere more than 300C higher than I currently go. If the fire had gotten to those temperatures, the sand underneath the fire would have probably been fused. Oh well.
So, how else can I get some surface coating? I may be able to use glazes, but this becomes more difficult in a pit fire. I’ve considered building firing boxes, not unlike Saggar containers. My first attempt didn’t go so well (see the wet clay section above). I’ll just have to build the boxes better and stack the pieces in a way where they don’t stick. Maybe I’ll make some simple clay shelves to go in there? Maybe make the shelves out to be coasters to be useful after the firing too. The only issue is if they break in any way or the system falls over. Perhaps the box should be pyramidal instead of straight up, to give it a solid foundation and keep a central point on top to open and use to introduce coloring materials.