Marianne Lombardo on sat 1 dec 01
I would appreciate if one of the firing/glazing gurus could tell me if =
this information is correct?
1200F-1400F Carbon gases burn out (fire at 50F/hour)
1450F-1550F Organic matter burns out (fire at 100F/hour)
Is there anything else happening during the firing from 1550F up to =
1940F (^04) that requires very slow firing at a particular temperature?
Through trial and error, I am trying to develop a reasonable but =
effective firing schedule with a manual electric kiln with simple on/off =
switches. I have to babysit the kiln and watch temps with a pyrometer =
and play with switches. Pinholing has now been reduced to only an =
occasional one, but I would be happier to eliminate them entirely.
Thanks,
Marianne Lombardo
Peterborough, Ontario, Canada
Can I fire as fast as I want from 1550F-1940F?=20
Ron Roy on fri 7 dec 01
Hi Marianne,
Lawrence and West say -
Chemically bonded water leaves 450-600C (842-1112F) but most authors
disagree about this range.
Organic matter is oxidized and removed from 300 to 700C (572-1292F) - they
are talking about whiteware bodies.
I think it goes on further than that based on observation - smoke from
kilns during bisque firing - perhaps because of the kinds of clays we use
and speed of firing or perhaps the sulphur starts and ends later than the
carbonous material.
The next major change after is meta kaolin changes to spinel 980C ( 1796F)
not a problem for potters.
I think 50C per hour is very slow but it may be necessary for thick ware
which is stacked very tightly and the kiln is so tight that no replacement
oxygen is available during combustion of organics.
I would say 100C per hour is OK for most of us - especially if a vent
system is running.
Even then - if lids are fired on, ware stacked or fired upside down you
might still have a problem with some clays - depends on how much carbon and
sulphur is present.
Remember - if you insert a sliver of wood or cardboard into a spy hole
during the later stages (after red heat) and you see flame inside the kiln
there is excess oxygen - if it only smokes in there you are making charcoal
- which happens sans oxygen.
Be careful now - don't use short splinters - it's gonna get hot!
In the end - slow firing solves problems - firings are more even and ware
is heated more evenly - results are more consistent even if ware size
changes and kilns last longer.
RR
>I would appreciate if one of the firing/glazing gurus could tell me if
>this information is correct?
>
>1200F-1400F Carbon gases burn out (fire at 50F/hour)
>1450F-1550F Organic matter burns out (fire at 100F/hour)
>
>Is there anything else happening during the firing from 1550F up to 1940F
>(^04) that requires very slow firing at a particular temperature?
>
>Through trial and error, I am trying to develop a reasonable but effective
>firing schedule with a manual electric kiln with simple on/off switches.
>I have to babysit the kiln and watch temps with a pyrometer and play with
>switches. Pinholing has now been reduced to only an occasional one, but I
>would be happier to eliminate them entirely.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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