Hadar’s Blog

Firing with core material at high-fire schedule

Following my recent breakthrough in firing schedules, the next thing I tried was to fire Low-Shrinkage Steel XT in combination with core material – specifically, Creative Paper Clay. My suspicion was that (1) the paper clay might not burn off without pre-firing; (2) the paper clay might interfere with the sintering of the steel.

Here are the fired pieces:

All 3 pieces sintered fully after 2 hours at high-fire schedule with no pre-firing. The paper clay behaved exactly the same as with pre-firing; it turned into dust and buffed away.

The third piece is a combination of Low-Shrinkage Steel XT and Bronze XT. Bronze XT was only 1 card thick (see pp. 107-115 in my book Metal Clay Practice). It sintered just fine.

Increasing ramping speed at high-fire schedule

All my tests are done in a brick kiln. Muffle kilns ramp faster, even if they are set to the same speed. It may have been that in my previous experiment, the steel sintered without pre-firing because it had a lot of ramping time. To rule it out I increased the ramp. Total firing time at high-fire schedule was about 3 hours.

The results are surprising:

Before firing

After firing

1. Low-Shrinkage Steel XT by itself, as well as Low-Shrinkage Steel XT in combination with 2-cards thick copper and bronze XT fully sintered.

2. No cracking occurred as often happens with pre-firing steel clay on a stove top. No repair was necessary.

3. No fireable stones clouded, as they sometimes do, even at lower temperatures.

Firing color-patterned pieces at mid-fire schedule for only one hour

This is something I did not intentionally test, but happened to notice. As you may recall from the previous posting, less than 100 grams of clay can be fired for just one hour after pre-firing. The surface of color-patterned pieces, when fired for only one hour in a batch that weighs less than 100 grams, comes out significantly more flush and smooth than in a 2-hour firing. That makes it much easier to finish.

The Instruction Manual is not updated yet. There are some findings for which I have no explanation just yet, but they seem to imply that further improvements can be done to the firing schedule.