Posted Firing Schedules in Tip Sheet 7

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Posted Firing Schedules in Tip Sheet 7

Postby Stephen Richard » Sun Apr 10, 2011 7:32 am

I was wandering around the education section of your site and wondered about something I found in the firing schedules for making a bowl.
http://www.bullseyeglass.com/pdf/techno ... eet_07.pdf
On page 3 you suggest some firing schedules/. In the one for firing flat you have a 1 minute soak at 371C. I wonder what the purpose of this may be?
When slumping that fused blank you do the annealing cool at 56C/ min rather than 80C/min. I wonder what the reason for this is? And is is a general policy to reduce the annealing rate in each successive firing?

Stephen
Stephen Richard
 
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Re: Posted Firing Schedules in Tip Sheet 7

Postby marykaynitchie » Tue Apr 26, 2011 2:12 pm

Hi Stephen,

So sorry for the delay in answering your question. I had a question about the answer I wrote, and sent it off to a technician, got my reply, and then forgot to post! Here it is:

Hi Stephen,

Thanks for asking! Re the 1 minute hold: years ago there was a notion among at least some of the technicians in the R&E department that a programmer is less prone to error when executing a 1 minute hold compared to a 0 minute hold. Both work, and I haven't heard anyone mention that in an instructional setting for a long time, so maybe this is not true anymore. But it also doesn't hurt anything. And it was pointed out to me that if someone was using a really old controller, using 1 minute instead of 0 might work better for them.

Re the 56º C rate compared to the 83º C rate, we do reduce the annealing rate during a slump firing compared to the initial firing. Explanation: as noted in TechNote 4, Heat and Glass, on page 8, "Because the slumped piece will be in contact with a mold that will have some thermal mass and may or may not be of a completely uniform thickness, and because a slumped piece will tend to cool unevenly," compared to a flat piece, "both the anneal soak and the anneal cool should be more conservative than they would be for pieces of comparable thickness that were merely flat fused."

Thinking about your question helped me spot an error in the fusing cycle shown in TipSheet 7: the Fahrenheit rate shown in the Basic Fuse Cycle, Segment 4 is 100º F, the same shown in the Basic Slump Firing. I think this is an error--the Fahrenheit rate in Segment 4 should be 150º F. So we will correct that and repost the document to our website.

Mary Kay
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Re: Posted Firing Schedules in Tip Sheet 7

Postby Stephen Richard » Tue Apr 26, 2011 2:42 pm

Thanks all for answering and explaining the reasons. Common sense, of course, but now I know they are backed up with experience.

Thanks again.
Stephen
Stephen Richard
 
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