Posted 03 June 2010 - 03:19 PM
Try it and see! I think that you'll want to fire them first or the 'attrition rate' will be very high.
Posted 04 June 2010 - 05:35 AM
A local Native American tribe has been doing a variant of this for, according to archeologists & historians, 2500 years. Prior to the advent of electric stoves, pots were heated in fireplaces or open fires. Nowdays the pots are pre-heated in an electric stove, starting pots at the stove's lowest setting and then slowly (over a period of 4 or 5 hours) raising the temperature to 500 degrees. When pots have been held at that temperature for at least an hour, they are carried to an outdoor fire built on the ground (not in a pit) that has burned down to coals. The larger coals are raked to the outer edges of the fire circle and the pots are placed in the smaller coals and then covered with branches or slender pieces of wood that almost immediately catch fire atop the pots. After this fire has burned down somewhat, any unburnt branches are carefully removed so that pots can be covered with a material that will produce smoke, such as pine bark. The pots are removed from this last firing while the pine bark is still smoking (in order to preserve some unsmoked areas on the pots). In such a firing, breakage and cracking can claim all the pots -- or none of them. I've seen ten coil-built pots fired this way with no breakage or cracking in any of them, but I've also seen an 80% loss in this type of firing. In my somewhat limited experience the typical loss is around 25%, with a long drying period prior to firing being a major factor in loss prevention.
I have done roughly the same thing with sawdust by preheating the clay pieces in a stove, and then placing them on a layer of bricks covered by sawdust in a metal trash can which has been drilled with a 1/4" drill bit every 12 inches or so. I add sawdust as I layer the (in my case) clay sculptures, topping it all off with a 6" layer of sawdust. I add crumpled newspapers to the top, light the papers, cover 90% of the opening with the trash can lid, and leave it until the smoking has ceased and the sculptures are cooled. With this technique I have experienced cracking in 25% of the sculptures, with occasional breakage due to poor stacking in the trash can. To address the breakage problem, I'm planning to experiment with circles of screen wire propped on perimeter bricks between the pottery layers to prevent one layer falling onto another as the sawdust burns away.
Hope this helps....
Posted 07 June 2010 - 11:26 AM
I have done a barrel fire. We had some pieces in it that were bisque fired, and they all made it without chipping, we also had some that went in green and the results were more mixed. The most common loss was at attachment points, if a decoration was not well applied it came off, but those that were well-attached made it through just fine. The second type of loss was during the firing. This only happened with the pots that were on the side of the barrel and did not get fully fired or that might have had uneven heat applied to them. The third type was those that broke with unloading, and they were very incompletely fired and very fragile.
I think if I was able to use a pit instead of a barrel (limitation of the site we were doing it at) it would have worked better, there would have been more insulation. It was also a windy day so the heat being blown away from the sides of the barrel. We did make sure the greenware was very dry before putting it in, the pieces that we were unsure of we cooked in a regular oven, bringing up the temperature slowly to around 300 then turning it off and leaving the door closed so it cooled slowly. If we had another week to let them dry I think that this step would not have been necessary, but we only had one and a half weeks between the building day and the firing day. The stuff I made before the firing day I did not dry in the oven.
The fuel was a mix of wood, cardboard and wood shavings.
Here are some pictures, of the barrel on fire, a broad pic of everything being unloaded, and more detailed pics of the stuff I made. The first few have before and after pics as well:
Posted 08 June 2010 - 05:42 AM
yeah, form the pieces so they shrink uniformly, for example, a sphere or semi sphere: check the designs of pueblo pottery. Remember to use clay with grog or other appropriate thermal shock design such as raku clay. Paint the terra sigalatta over this for burnished surfaces, etc. And take your time with the firing.
h a n s e n
Stone House Studio, Alexandria, Virginia
Posted 11 July 2010 - 12:05 PM
when teaching primitive firing techniques and firing local clay using a pit (in the ground hole) I did the following:
1. dig a hole about 2-3 ft deep.
2. cut an edge about half way up the wall that will support a grate or square BBQ grill. Can use more than one grill in a longer hole.
3. start a wood fire in the lower part of the hole, letting good coals accumulate.
4. place the grate on the ledge.
5. let the pots absorb the heat from the blazing fire.
6. place the pots upside down on the grate.
7. cover with well dried cow pies to a height at least 1-1.5 ft. above ground level.
8. Let it smolder. You can use sheet metal to seal off wind for better blacks.
9. AFter a few hours, flames will burst to the surface.
10. Let it cool and unload.
Posted 11 July 2010 - 12:10 PM
When firing a barrel with sawdust, I have always fired bisque ware. This firing system is fairly quick and may be too quick for non-bisqued pieces.
Maybe you could preheat on a bbq before loading the barrel.
For some added fuel, I place newspaper, sticks, charcoal briquets and large sawdust. I am respectful of fine sawdust after witnessing spontaneous combustion when fine sawdust blows into the air.
You can play around with additives, the most common being salt and copper carb. or miracle grow.