mel jacobson on sun 20 may 01
from a happy potter.
good report.
mel
>Wanted to let everyone know the fun I'm having with my "new"
>combination gas/electric kiln. I followed the conversion directions
>published on ClayArt by Mel Jacobson and Nils Lou, as well as the
>advice of John Post on where to buy the burner, valve and regulator,
>etc. A hearty THANK YOU to everyone who has posted to ClayArt with
>all the how to's and advice. I'm getting good results with a number
>of standard c10 glazes (recipes in a separate post). It is fantastic
>to be able to do c10 reduction at home in my back yard... Since
>directions for kiln conversion have previously been detailed, I
>thought I would share my novice experiences in firing schedules and
>procedures, to those wishing to try this.
>
>I converted an older Duncan DK-820, typical 8-sided ~3 cubic ft
>electric kiln. I added new ITC 213 coated elements and sprayed ITC
>100 on the inside. In two weeks, I've had 4 firings to c10 using
>gas/electric. Pots are bisque fired before glaze firings.
>
>DISCLAIMER: I'm a novice to gas firing. The procedure I put
>together below is working for me. Your mileage may vary... feedback
>and input is welcomed on how to improve the information below!
>
>Firing Schedule/Procedure
>=========================
>Important...BEFORE loading the kiln, I place and anchor the bunsen
>burner underneath, centering it to ensure the flame comes up through
>the 1.25" hole in the bottom of the kiln. This allows easy lighting
>later during the firing, without having to adjust placement of the
>burner while kiln is at 1650 degrees! Also, before the kiln is
>loaded, you can easily see if the burner is centered underneath by
>looking inside the kiln chamber through the bottom hole. I anchor my
>Bunsen burner with a brick on either side of its base, and
>cover/insulate the gas hose with 3" x 18" scrap of Kaowool, for the
>portion of exposed hose underneath the kiln.
>
>Using staggered half-shelves to fire pots has worked best -- I found
>that my one firing of 5 platters using full shelves had spotty
>reduction, seen by reduction patterns on the bottoms and sides of
>platters. My first shelves sit on 1/2 inch posts, with about a half
>inch between the two shelves (in the middle) so flame can enter the
>firing chamber easily. I would appreciate any advice on getting more
>even reduction using full shelves, so that I can fire platter or wide
>bowls.
>
>The firing schedules have been fairly consistent. My kiln dials have
>four basic settings -- LOW, MED, HIGH, and HIGH-FIRE -- to help you
>interpret for your kiln:
>
>Hour
>0:00 - 1:00
>Bottom dial LOW, top dial LOW.
>Bottom peep closed, top peep and lid hole uncovered.
>1:00 - 2:00
>Bottom dial MED, top dial LOW.
>Bottom peep closed, top peep and lid hole uncovered.
>2:00 - 3:00
>Bottom dial HIGH, top dial MED.
>Both peeps plugged, kiln shelf covering hole in lid.
>3:00 - 5:00
>Both dials = HIGH FIRE for ~1-2 hours, or until 1650 degrees F
>reached on Pyrometer
>5:00 - 6:15
>Both dials = HIGH FIRE, burner lit**.
>Top peep open, kiln shelf covers half of lid hole.
>This is my version of medium/heavy reduction, which will continue
>from ~Cone 010 to Cone 5 approximately. Four to six inches of flame
>shoot out the hole in the kiln lid, as well as the top side peep
>hole. Bottom peep is plugged. Smoke is emitted from flames out both
>side and top. I'm assuming that more smoke equals a bit more
>reduction (I'm a newbie to this...opinions welcomed!), so I keep the
>lid hole covered such that a fair amount of smoke is emitted with the
>flame.
>
>**Using advice from Nils Lou on Clayart. I open the top peep hole
>and slide the kiln shelf back to expose the top hole in the lid. I
>then start the flow of gas to the burner -- it lights itself because
>of the high heat directly above it in the kiln. Flame appears
>through the top after a couple of seconds. I then push the kiln
>shelf back over half the hole in the lid to start reduction. (Having
>never fired a gas kiln before...this is probably the scariest part of
>each firing for me, as I'm still not comfortable with the use of
>propane and flammable fuel. However, each firing has increased my
>confidence in the procedures... advice on how to make this safer is
>welcomed!)
>
>6:15 - 7:00
>Both dials = HIGH, bunsen burner still lit.
>Slide the kiln shelf to cover just less than half the hole in the
>lid. Amount of smoke in flame reduces, but some smoke still
>present. Height of flame out the top increases, while length of
>flame out the side decreases slightly. This is my version of
>lighter reduction, which, by the pyrometer, is happening between Cone
>5 - 9. During the last 5 minutes of this firing period, I uncover
>the top hole completely, and plug the peep hole on the side. Very
>little smoke can be seen in the flame during this last five minutes.
>7:00 - 7:15
>Both dials = HIGH, gas turned off.
>Kiln shelf slid over to cover the top lid hole. Wait until cone 10
>drops in the kiln sitter. I hope that I'm firing in oxidation from
>approximately cone 9 to cone 10.
>7:15 - 7:30
>After sitter shuts kiln off, turn kiln back on. Bottom dial = HIGH,
>top dial = MEDIUM. This I consider to be a short soaking period,
>near the peak temperature.
>
>I then set my timer to 5 hours, and set both dials to LOW. This
>helps cool the kiln more slowly. I find that I can open the kiln
>safely after a total of 12 hours from the time the kiln was initally
>put on "LOW" to fire down.
>
>=========================
>
>I hope this is useful to those attempting to work with a converted
>gas/electric. Thanks again to all who've posted much useful advice
>before me...
>
>Kind regards,
>Dan
>
>p.s. if you would like to receive some digital pix of the setup, I
>can email them. Still don't have a web site set up...
>
>
>--- In clayart@y..., mel jacobson wrote:
>> i have had several reports this week from folks working
>> with the new gas/electric kilns.
>>
>> they are very happy people...saw downloads of pots...very
>> nice. rich reduction. typical reduction color and texture.
>> they are doing it.
>>
>> this pleases me a great deal.
>> keep the reports coming in....your research is vital.
>> mel
>> from the farm in wisconsin
>> http://www.pclink.com/melpots
>>
>>
>______________________________________________________________________
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>
>
>
from the farm in wisconsin
http://www.pclink.com/melpots
Tommy Humphries on sun 20 may 01
As I read this I thought of a question, that I don't think has been
addressed (unless I missed it somehow) concerning the use of ITC 213 on the
combo kiln.
The elements are coated... this has been made clear from day one, but what
of the metal parts of the kiln sitter? I believe that the actuating rod
and the cone pins should be replaced with new, and coated just like the
elements...
Am I right Mel???
Tommy Humphries
----- Original Message -----
From: "mel jacobson"
To:
Sent: Sunday, May 20, 2001 4:30 PM
Subject: Re: gas/electric -- a firing schedule (long)
> from a happy potter.
> good report.
> mel
>
> >Wanted to let everyone know the fun I'm having with my "new"
> >combination gas/electric kiln
> >. Wait until cone 10
> >drops in the kiln sitter
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