pjomjp[ on mon 26 may 97
Rising Heat:
In general terms heat (thermal energy) always moves "downhill"-- from
hot to cold. This has been noted here. Owing to this behavior,
universally speaking, someday the whole universe will be the same
temperature -- not a good idea, but the law -- the Second Law.
Hot air most certainly rises -- so does hot water, hot glass or any
other fluid with a temperature gradient within it. Anyone who doesn't
believe that is welcome to present us their theory as to why chimneys
work as they do -- we'll pass it along to the Nobel committee for
consideration,too.
Cracks:
I didn't read much of these threads, but would submit the following in
response to what little I did see.
In order to crack there must be some sort of strain imposed on the ware.
Most cracks in ceramic ware are a product of the strains the ware
experienced when drying. The cracks were there before the firing and
merely opened-up through the firing process. The ware will crack where
it's weak. The weaknesses which determine where those cracks occur were
established in forming.
The weaknesses can be established by several means. One of the more
important is in the extrusion of the pug. Place a wad of extruded clay
in the freezer overnight to see how the differential flow through the
extruder's die can establish weaknesses. These can easily survive
forming processes in a variety of forms.
Bob Hanlin notes:
>I do know that since I've started compressing the bottoms of my pots >I've had
Could be that this maneuver compacts a lamination relic of the extrusion
process.
Hot Air:
>My new question is about the praticality of omnidirectional heating. >If I wer
Assuming perfect combustion, we might consider a kiln's efficiency to be
a function of how much of the heat input to the kiln actually does the
work of heating the ware. This being the case, the answer to your
question is no. It would be more "efficient". Placing the burners on the
floor -- as is customary -- permits the combustion gases to remain
resident in the kiln as long as practical to transfer their heat to the
load. Seeing that _hot air_ rises, putting the burners in the arch of an
updraft kiln merely places these gases in a position such that they can
leave the kiln almost immediately. Thus, such a design is, on its face,
flatly stupid. One would also argue that updraft kilns are, as a rule,
the worst possible design choice in almost any case.
KPP --
w/ Tom Jobim & Frank Sinatra on the radio -- very strange. They're
singing A Garota de Ipanema/ The Girl from Ipanema, however, the words
in English an Portuguese have no relationship whatever and Frank is
singing one line in English with Jobim singing the next in Portuguese.
Very weird and very funny. "Olha que coisa mais linda, mais cheia de
graca" isn't "tall and tan and young and lovely".
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