Shortening the Time Between Phases – Follow-up

Before I started to shorten the time between firing phases, I did not have a chance to check the pieces after the first phase, since I had never taken them out of the carbon. Now that I have done it quite a few times, I can tell that there is an important difference between the clays at this point (after the first phase), and if you are not aware of this difference, you may end up destroying your piece.

Bronze and White Bronze are quite stable after the first phase of firing, and if you handle them carefully (light touch, no tweezers), they should be fine. This is not the case with copper, and even less so with steel. These two metals are so fragile at this stage that they may break as a result of even the slightest tilt of the box when you take it out of the kiln (not to mention the effect of actually touching them).

The first phase is meant to burn away the binder. At the end of this phase, there is actually nothing to hold the metal particles together. The removal of the binder allows the particles to get closer in the second phase, until they actually bond and become a solid mass. This is why the pieces are so fragile at the end of the first phase. It seem a miracle that the do stay together.

For now, I would like to avoid discussing why bronze and White Bronze are less fragile after the first phase. I would be glad to discuss this in actual workshops. The point is that you need to be extra careful with copper and steel, and if you don’t trust yourself, just take the box out of the kiln carefully and let it cool naturally. It is recommended to use rigid boxes that don’t wobble, as a ceramic blanket is likely to do – you can use a fiber board box, or even a mixing bowl (just remember to adjust the temperature for each type of box).

Firing Steel and Copper

If your piece is constructed of steel or copper, or a combination of steel and copper, with no bronze or White Bronze in it, fire at 1650°F/900°C, as the updated Instruction Manual suggests. They will not be very strong at a lower firing temperature.

When we fire them with bronze and White Bronze, we are actually under-firing them since bronze and White Bronze will not tolerate such high temperatures. In that case, it’s the bronze or White Bronze that give the piece its strength.

To quote the unforgettable Sgt. Phil Esterhaus of Hill Street Blues: “Let’s be careful out there!”

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