Diary and notes from a secret ceramics studio.
moisture can cause the cones to weaken- we don't trust them.They are cheap- use new ones.
My understanding (and I don't know the full thermodynamic theory here) is that something happens in the cones while they're going up to where they begin to deform and drop. Not dependable after that, or so I've been told. I've never tried it, but I think Meredith's "use new ones" is the best idea.
If you don't have any new ones around. My husband(by the way he is a ceramics lab tech) says that the cones haven't falling is just like the glaze that is under fired, re-fired it to the proper time and temperature and it will work.
P.S. make sure your cone pack wasn't left out side or got wet at all because like any vitrified re-fired it can blow up. (again according to my husband...haa..)
I've done this with success, but the cones had been very underfired, ie hadn't even begun to bend. Also, I was refiring underfired ware, the same stuff that was in next to the underfired cones. I just assumed that any changes that had taken place in the cones would have taken place in the glazes and clays as well, so everything was pretty much equal. In most cases, I'd probably just use new cones, but here in Japan, Seger cones are the norm, and they cost about $2 each. Ouch!
Those are great answers... now I gotta test it!
My understanding is that the melting of cones works on the same principles as the melting of glazes, so I guess it would depend on how underfired they were. Remember, this is a question of heat work, not just the temp profile of the final firing. With glazes, it is not a simple question of the whole glaze melting all at once at a certain temperature. Rather, certain ingredients start the melt at a much lower temperature and then actually lower the melting point of other ingredients. How else would silica become part of the glaze melt, right?So I guess if certain ingredients of the cones had started to melt or sinter, then actual heat work has already been done, and any subsequent heating will require less heat work to achieve the bend of the cone you are looking for. This means that it wont be accurate anymore. Just to make this case I will give you an example. There was a potter in town here who used to fire a glaze that matures at cone 9 in his bisk kiln multiple times until it would finally melt. The first firing it would sinter, the next it would melt a bit more, and so on until it finally became a mature glaze. And all this was being done at around cone 04, not cone 9. Hope that helps.
Why don't you put them in with a new pack, then compare?
http://www.paragonweb.com/Kiln_Pointer.cfm?PID=361Sorry, had to repost as the URL was cut off.
Oooooo! Those are good!
It's my understanding that cones are effected by not just heat, but time subjected to heat. Taking that into consideration I think the partially used cones would reflect a false overfired result.:) Cindy
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