Since my last posting I have been working on a firing method that will be cleaner, cheaper, and shorter. I’ve finally found one. This method does not require a stainless steel box, uses a lot less carbon, requires no vacuuming, and leaves the kiln perfectly clean after firing. The kiln can be either cold or hot both before and after firing, overall firing time is shorter, and firing temperature is lower. [Edit on 2/1/2010, 8:10 a.m. PST: I’d like to clarify that as of now, I have only tested this method with my Quick-fire clay. Thanks to readers who asked me to clarify this.] So here goes:
[Edit on 2/3/2010, 4:00 p.m. PST: STOP! These instructions have now been updated, and the latest version can be found here.]
1. Place your ceramic/fiber kiln shelf on posts to position it high in the kiln.
2. Fold a a fiber blanket into a “box.”
The fiber blanket can be re-used. It is quite inexpensive to buy it in rolls from glass fusing suppliers; you can then cut it with scissors to your desired dimensions. The one I bought was 1 inch thick, and I separated it into two layers a half-inch thick.
You can also purchase a rigidizer from the same source (these are normally used to make slumping molds for glass fusing). This will stabilize the shape of your box.
3. Line the inside of the blanket “box” with a ½” layer of carbon.
4. Arrange your pieces on the carbon bed. As usual, avoid the center.
5. Cover the pieces with another ½” inch layer of carbon.
6. Cover the carbon with another piece of blanket, creating a “sandwich.”
You can start the firing in either a cold or a hot kiln.
Top loader brick kiln: ramp at full speed to 1450°F/788°C
Front loader muffle kiln: ramp at full speed to 1530°F/832°C
(You may find that this temperature is too high for bronze. If it is, flat bronze pieces wil warp some. You can either hammer them down after firing or lower the temperature.)
Hold for 1:00 hour.
You can take the pieces out of the kiln while still hot or wait until they cool down. Overnight firing works fine. If you take them out hot, use heat-protective gloves. The sandwiched part is actually on fire!
After firing, most of the carbon turns into ash. Pick up the fiber “box” from both ends and lift it out of the kiln. The kiln will be perfectly clean.
Almost all of the carbon will have turned into ash, including the bottom layer. Just throw it away. To retreive your pieces you can pour it hot through a sieve into a metal container.
This schedule works best with bronze (even with very thick pieces), with mixed pieces, and with average sized pieces of copper. The bronze circle on the right is ¾” in diameter, ¼” in thickness.[
I am now working on a schedule for thick and/or large pieces of copper, starting with the following options:
- Hold for 2 hours, or
- Hold at 1000°F/538°C for 0:30 minutes to 1:00 hour before proceeding to the goal temperature, or
- Raise the temperature. Copper can be fired as high as 1770°F/965°C (as in the schedule “Hot Firing” in the instruction manual for Quick-fire clay).
As soon as I have reliable results for copper firing, I will post them and make the necessary changes in the instruction manuals.