View Full Version : Crucible question

Michael Mattei
05-07-2012, 01:55 PM
I have a question about breaking in, for lack of a better term, a new crucible. I'm in the middle of building a small electric furnace to melt glass to roll into sheets for my leaded glass work. I bought a pair of crucibles, changed my design and have these sitting.

I saw Skutt is now making a crucible furnace, one that will perfectly accommodate these crucibles so I bought one and it'll be here Weds.

The crucibles are from Emhart Glass-#GC-138-their FOMLAC composition

My questions,

1)What is the firing schedule to bring these up to temperature?
2)Should I have cullet in it from the start or should I fire it, lower the temp and then charge it.
3)If I should fire first and than lower to charge; lower to what temp to charge?

Thank you.

As an aside Peter, I'm taking your class next June and am kinda overwhelmed by your glass coloring conversations here. I guess I'll have a year to make lots of mistakes.

Pete VanderLaan
05-07-2012, 03:47 PM
Bring it up to 1000F at 35F per hour. Hold at 1000 for 2 hours. Go from 1000F to 1100F over four hours, then back to 35F per hour until it is glowing. Then just turn it up. Charge when it's hot.

You can just barely cover the floor of the pots with cullet when you turn it on. Don't fill until you're hot. Since you don't say what cullet you are using, I'll presume spectrum nuggets, so melt at 2175F. I encourage you to try High Temp crucibles in the future. Those nuggets are going to go after your kiln.

Michael Mattei
05-08-2012, 05:23 AM
Thank you Pete

Rick Sherbert
05-08-2012, 06:39 AM
Hold at 1000 for 21 hours?? Seems really long. Typo or for real?

Cecil McKenzie
05-08-2012, 08:09 AM
I hold for 8 hours at 1050. Same brand but a little bit larger crucible. Seems to work for me. My furnace is gas though and has a bag wall so is protected from flame.

Pete VanderLaan
05-08-2012, 08:17 AM
typo, should be 2 hours. thanks rick, shoot the horse now please. It's still young and gullible.

Any time I advise on a heat up schedule, I err on the serious side of caution. LaCledes are very fine grain compared to the coarse grain tabular alumina pots and need respect. Lecledes are also disproportionately thick compared to the others. Quartz inversion begins at about 980F and continues until about 1100F. I would not park in the middle of it as a habit.