Breakthrough in Firing Schedules
With the encouragement of the participants in my most recent intensive, and with their kind permission to experiment with their pieces, important progress has been achieved in shortening the firing schedule:
Low Shrinkage Steel XT by itself, as well as Low Shrinkage Steel XT combined with small amounts of copper and Bronze XT do not require pre-firing.
Two big rings that were fired in a brick kiln for 90 minutes at high-fire schedule (1700°F/926°C) with no pre-firing came out completely sintered. The total weight of the two pieces together was less than 100 grams. They are not shown here because I have not done any finishing on them. An attempt to fire a group of pieces weighing more than a total of 100 grams required re-firing.
The batch in the photo below was fired for 2 hours with no pre-firing. The weight was a little over 100 grams. (It looks like a lot more than 100 grams, but keep in mind that steel clay is very lightweight.) All sintered fully.
Here are photos of the individual pieces:
Hollow forms did not crack at the seams, as sometimes happens when they are pre-fired.
Pieces made of copper and Bronze XT, fired at the same temperature, did not sinter. However, small amounts of these clays did sinter when added to steel pieces.
The overlays were rolled 2 cards thick before sanding. All sintered perfectly.
The second experiment was done at mid-fire schedule. After pre-firing, 100 grams of copper, bronze, and Brilliant Bronze were fired for only one hour. All sintered. A batch of 10 big rings only sintered partially. My theory is that the bigger the total amount of metal fired, the more time is required for the heat to reach all of it. What supports this theory is that all repairs, fired for 1 hour with no pre-firing, were successful.
To sum up:
1. Low-Shrinkage Steel XT by itself, as well as Low-Shrinkage Steel XT combined with small amounts of Quick-fire copper and Bronze XT, can be fired for 2 hours at high-fire schedule with no pre-firing.
2. Up to 100 grams in total of Quick-fire copper, bronze and Brilliant Bronze can be fired for 1 hour at mid-fire schedule after pre-firing.
3. Repairs for any of the clays can be done with no pre-firing for 1 hour only.
I am not updating the instruction Manual just yet, since I plan to continue experimenting. Hopefully, more results will be posted soon.