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View Full Version : Which Crucible to Heat


Paul Bevilacqua
01-29-2012, 03:49 PM
I recently had an electrical hiccup that caused my crucible to cool at an unknown rate. I found it after 20 hours with a temperature of 300 degrees. I finished cooling and took the pot out and examined it. It has 4.5 inches of glass in the bottom of a 12 inch pot with almost no cracks in the glass (photo attached). I am wondering if the lack of cracks indicate a slow cooling. I have another backup pot that has 3 inches of cracked glass in the bottom from a similar event 2 years ago. Both are pristine on the outside.

Pete VanderLaan
01-29-2012, 04:45 PM
Start the one up that is warmer, now. Go at 20F per hour until you get to 1000F, then hold for four hours. Then go to 1100F over five hours and hold at 1100F for four hours. Then go up at 40 F per hour until it's glowing all around. Then, turn it up.

It may work, it may not but I would say the same thing about either pot. Chances are it will be fine with a somewhat shortened life, about 30 percent usually.

Paul Bevilacqua
01-29-2012, 06:26 PM
Thanks Pete. It's done.

Greg Vriethoff
01-29-2012, 09:06 PM
Wow, that's some serious devit on the surface...if I'm reading the photo correctly.

Rahman Anderson
01-29-2012, 09:31 PM
This is not advice but it is true. I have been working out of that size pot for almost 19 months. I bring it up 100 degrees an hour (not that my ceramic kiln can even keep up) hold at 1000 for 2 hours then 100 an hour to temp. Probably not good advice but I think that pot size is tough. A big pot will break WAY easier then a small one. My pot is on it's second furnace(read ceramic kiln) and still fine. I have done this several times with it over half full. Yes I do have a spare from Pete sitting in wait. Next summer I plan to have a spare furnace (yes kiln) sitting in wait as during my 90 day tourist season as few days down sucks. Yes I do know how different a real furnace is but I plan to build a business before getting in for the big bucks. First I need an employee so I can get 300#s out of it in a week. That person is more expensive then the furnace! If you have an idea what you are doing a shoestring works. Sure we all want it perfect but blowing glass for yourself beats gathering out of a Rolls Royce for someone else! ('cept the pay ain't always as consistent) But really do what Pete says and you will be smarter.

Pete VanderLaan
01-30-2012, 05:06 AM
Rahman, If I had a boat, you would be making my payments for me. I agree that it's cautious but then again, it's not my pot. For some people, that 20lb pot is just as important to them as that 400 lb pot is to someone else. I get some people who really sweat the details buying a single 65 dollar pot. Others buy 3 400lb'rs at a time to cut shipping costs. If you read the instructions Spruce Pine gives on melting batch, you just wouldn't do it. It's erring on the side of the lowest common denominator.

When I used to make color commercially, I would put pots in the furnace at 6:00AM and be melting in them by 5:00PM. They were not small pots but I had about 50 of them sitting, ready to go. A half full cold shut down pot is however a different animal.

Pete VanderLaan
01-30-2012, 05:10 AM
A final thought ( I'm never really final). If you are going to refire a pot, the last thing you want to do after an accident is to take it out and examine it. High Alumina pots really break up easily being jarred. Just refire. Don't move it unless it is totally free on its stilt wihtout knocking it loose

Rahman Anderson
01-30-2012, 03:10 PM
I was not meaning to disagree with you at all Pete. I would have been more careful had I not felt a more pressing need to be open while people were around. I would have been more careful had I not had a replacement pot here ready. The first time I did things much slower and ordered a pot before I started trying to bring up the very full one. I am just impressed with the pot I have been using and the abuse it has held up through. I do plan to change it out next time I shut down. So how many pot changes gets me a ride on this boat?