Paul Stubbs on tue 14 mar 00
Dear Jeff and Rick and all
My pitch on this "thread" is system I call "steam drying"
Pots can blow up at this critical phase because a relatively dry
atmosphere in the kiln will create reduced permeability on the outside
surfaces of the work this barrier may cause steam pressure to reach an
explosive level. The method is particularly valid if you are firing
"difficult pieces" i.e. thick full of air bubbles or made from very fine
clay.
so in an electric kiln
CLOSE ALL VENTS
set energy control to as low as it will go,
10% on the energy regulo in the UK.
120oC on the controller
"soak" setting on.
Temp creeps up to set point gently, important, particularly if the work
is dry! I would suggest 2 hours min for this. The aim is to raise a good
hot sweaty atmosphere that will encourage the clay to dry from the core.
This phase can run as long as it takes even 24 hours if necessary,
When you are sure all the steam has escaped through all the usual gaps
or through the kiln walls then you should remove the top vent and crank
up the firing rate for the latter stages of the firing leave the vent
out till the end point in bisque firing is reached. Your kiln will last
longer if you do!
So if the kiln technicians are still blowing up your work tell them
about this system, there is no excuse for work that is blown up in
kilns! The "system" can be used in fuel burning kilns too.
Apologies to all those grandmas!
--
Paul Stubbs
2 Rosebank,
Queen Street,
Keinton Mandeville.
Somerset.
TA11 6EQ
England.
vince pitelka on wed 15 mar 00
> so in an electric kiln
> CLOSE ALL VENTS
Paul -
I am a little concerned about this advice. During the water-smoking period,
a supply of oxygen is critically important, to alow the oxidation and
outgassing of organics, carbonates, sulfates, nitrates. If you close all
vents you are holding in the steam, but you are also preventing this
oxidation, and that can result in carbon/sulfur coring and later problems
with bloating and blistering. The solution is to fire slower, but leave the
spy-holes open to provide a small supply of oxygen passing through the kiln.
Best wishes -
- Vince
Vince Pitelka
Home - vpitelka@dekalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
http://www.craftcenter.tntech.edu/
rickmahaffey on wed 15 mar 00
Paul,
In an old text I have on drying ceramics the advice "boils down" to
drying the ware in High Heat and High Humidity. One of the best
practical applications that I have ever seen of this principal, David
Keyes at Pacific Lutheran University placed a forced air heater in the
bottom of a metal cabnet that had a colpleof small holes in the bottom,
and none elsewhere. I could throw a pot and place it in there on a bat
and retreve it in about 20 -30 minutes to trim it for a demo. Great.
Rick
Marek & Pauline Drzazga-Donaldson on thu 16 mar 00
----- Original Message -----
From: rickmahaffey
To:
Sent: Wednesday, March 15, 2000 7:43 PM
Subject: Re: MORE ON Water smoking, Candling ETC
> ----------------------------Original message----------------------------
> Paul,
>
> In an old text I have on drying ceramics the advice "boils down" to
> drying the ware in High Heat and High Humidity. One of the best
> practical applications that I have ever seen of this principal, David
> Keyes at Pacific Lutheran University placed a forced air heater in the
> bottom of a metal cabnet that had a colpleof small holes in the bottom,
> and none elsewhere. I could throw a pot and place it in there on a bat
> and retreve it in about 20 -30 minutes to trim it for a demo. Great.
>
> Rick
>
Hi,
just to add my pennyworth, when I was making handmade roof tiles using
Berkshire Clay (red terracotta), which was a real pig to dry without
cracking, I found the only solution was in a specific drier where I could
have masses of moisture (humidity) and a high heat (drawing off from a
firing kiln). This gave unbelievable results with a fall from 20% loss from
cracking to just 1%. Some clays just have to be handled this way.
Happy potting Marek http://www.moley.uk.com
Paul Stubbs on mon 20 mar 00
In message , vince pitelka writes
>----------------------------Original message----------------------------
>> so in an electric kiln
>> CLOSE ALL VENTS
>
>Paul -
>I am a little concerned about this advice. During the water-smoking period,
>a supply of oxygen is critically important, to alow the oxidation and
>outgassing of organics, carbonates, sulfates, nitrates. If you close all
>vents you are holding in the steam, but you are also preventing this
>oxidation, and that can result in carbon/sulfur coring and later problems
>with bloating and blistering. The solution is to fire slower, but leave the
>spy-holes open to provide a small supply of oxygen passing through the kiln.
>Best wishes -
>- Vince
>
>Vince Pitelka
>Home - vpitelka@dekalb.net
>615/597-5376
>Work - wpitelka@tntech.edu
>615/597-6801 ext. 111, fax 615/597-6803
>Appalachian Center for Crafts
>Tennessee Technological University
>1560 Craft Center Drive, Smithville TN 37166
>http://www.craftcenter.tntech.edu/
>
Dear Vince
You make a good point. There are materials other than physically
combined H2o which have to be liberated so as not to cause problems such
as black core, bloating etc. My suggested system deals with the first
stage of the firing by allowing a useful high humidity to build up and
has a similar function as suggested by Rick and Mareck .
The posting goes on to say
"then you should remove the top vent and crank
up the firing rate for the latter stages of the firing leave the vent
out till the end point in bisque firing is reached. Your kiln will last
longer if you do!"
and of course this is where your suggestion fits, in my view, but not
necessarily earlier.
There are of course many ways to crack the proverbial egg!
Kind regards from a glorious Spring Sunday in Somerset.
--
Paul Stubbs & Julia Manning.
2 Rosebank,
Queen Street,
Keinton Mandeville.
Somerset.
TA11 6EQ
England.
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