Problem with “spiking”
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I experienced your “spiking” issue when I was first starting as well…
I went to the suggested firing schedules that Paul and Karen have posted on the site and was looking to compare…the main differences I noticed were they were going a little hotter on the full-fuse and holding for a little less time. I chose the single-layer fusing schedule since you’re doing jewelry components and they’re small, but the schedule is for larger pieces, and you could be a little less conservative on the ramp times and such.
Your 400° ramp is fine. On jewelry components I usually ramp a little faster, but 400° is safe.
I think the hold at 1250 for 60 minutes is unnecessary…the components are small. In Paul’s schedule, this allows the layers to squeeze bubbles out…60 is safe, and should minimize bubbles, but I usually don’t hold that long. Maybe 30 minutes at the most.
Now, your process temperature…I think this is where you’re having the problem. For a full-fuse, Paul has 1475° on the schedule, with a hold of 10 minutes. When I first started, I would use lower temperatures and hold longer…sometimes for up to 30-40 minutes, and I believe that this was causing my “spikes,” along with the use of the thicker, rougher fiber paper. Now I usually use the recommended process temperature, and hold for no more than 10 minutes. It varies by kiln, though, but not by much. I’ve had better results since I started going hotter and holding for a shorter time. I also used to open the kiln to “quick cool”, but I don’t do that anymore. I let it sit at the process temp for ten minutes, then let it ramp down to 960.
Anneal at 960 for about 30 minutes. Remember, jewelry components are small, and you won’t have as much of a problem with thermal shock.
And I will generally ramp down AFAP from 960 on jewelry components, although I’m much more conservative on larger pieces.
Paul may have other thoughts…but this works for me!