LIFE OF A USED DUNCAN KILN
Note: this article is /in progress/.
(IMG) The peep hole during a bisque
A photo-essay about a used Duncan kiln.
Epigraph
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Congratulations Irene,
It is heaven when that little used Duncan is all yours and you can get
your own surprises and prizes opened up at your very own studio from
your very own kiln...........I still using mine and mya the Lives of
the Used Duncan Kilns live on for ever!!!!!!!!!!!! and ever.
- Joyce Donahue, Sunday, October 13, 2002
Delightful, no? Irene and Joyce have been a great source of comic
relief during this project. The epigraph above--found somewhere on the
net while researching the kiln--always gives me reason to grin. It's
so wholesome how crafts people get along with each other and share in
the excitement of our pursuits.
Overview
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This text recounts my journey with a Duncan Energy Saving Automatic
Kiln EA-1029 (the Pro-/Plus/). The kiln was purchased by my ex-wife at
the height of her ceramics practice. As an act of goodwill (and out of
curiosity), I took on the tasks of repairing and maintaining the kiln,
as well as conducting its maiden (to me) bisque and glaze firings. As
my ex-wife has moved her interests elsewhere (into writing, happily),
and a ceramics practice can't contend against my other flourishing
interests, the old Duncan will soon find another keeper and become
part of stories beyond these words. Here's one small part of this
kiln's story. Enjoy!
Acquisition and Maintenance
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The kiln was purchased in Alma, a small town at the end of a windy
road along the Fundy coast. It had to be moved from a house basement
to ground level and then up a ramp and into a truck. With excellent
foresight I had brought a number of tools to help: a wheely platform,
a dolly, plywood, a toolbox, and some ratchet straps. Everything
together made the move quite easy. The stairs--narrow and steep--were
the one challenge, but with patience and teamwork no injury or damage
was made to person or kiln. Driving back posed no issue and unloading
was as simple as sliding the Duncan down the ramp and into the garage.
We did decide to run the kiln pretty soon after its acquisition--we
were eager, excited, and a bit concerned maybe that it was a
lemon. Well, shortly into the first cycle the fuse panel blew. I
enlisted an electrician to come over and set us up properly. The kiln
is rated for 50 amps and requires 240V. Being me, I already had 240V
installed from another hobby--printing. So it was just the amperage
that was missing. Getting that into the garage required laying a
larger conduit. So over an afternoon myself and the electrician
sweated and cursed as we fed a wire as thick as a cucumber from the
garage through an underground pipe, around the basement ceiling, and
into the house panel. Somehow, that experience left me thinking I'd
enjoy being an electrician.
The second attempt at running the kin wouldn't happened until June
2023. I decided that I should spend time with the old Duncan to get to
know her. All in all, I must have put at least 40 hours into that
kiln. I started by reading the service manual, which I luckily could
source online (Without this, I don't think I would have ever been able
to successfully service or operate the kiln.) Reading through the
manual I learned about the kiln's components and circuitry: the
elements, timers, and switches that make it hot! With this knowledge
in my head I set to doing the work. I checked each element with a
multi-meter. Only one of the elements was gone. A new one was ordered
from Tucker's and replaced with not too much effort. I checked the
switches, ensuring that the contacts were clean and conductive, and
the timers, making sure that they toggled the elements on and off at
intervals.
(IMG) Element contact cleaned up.
When I pulled the control panel off I found out that many of the
terminal connectors and hardware inside the kiln were rusted to hell
and back. No doubt, they would need to be replaced. So I numbered the
wires (ensuring I wouldn't forget what connects where), removed the
contacts and hardware, cleaned everything up, and the proceeded to
re-install the components. I did this all without error or
mistake. Afterwards, I checked the resistance across each element and
across all of the contacts instructed by the service manual (each
element produces a certain amount of resistance). This gave me
confidence that there was proper conduction in the circuit and that
heat wouldn't build up where it shouldn't.
The final step was checking that the kiln was properly grounded. The
service manual guided this process too. As I followed the instructions
I soon discovered that the metal exterior of the kiln was not
grounded. Yikes! Inspecting the control panel, I observed that the
metal contacts on the panel's edges had become rusted over. These
contacts were intended to carry the panel's ground over to the kiln
exterior. Obviously, the rust prevented conduction. I used sand paper
to remove the offending particles and then conditioned the
contacts. My final test revealed that everything was properly
grounded. Everything was in order--the next step was firing it up and
hoping for the best.
Bisquing
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(IMG) A loaded kiln before firing.
I loaded three shelves-worth of ceramics into the kiln. There were
four shelves in total but the bottom was left empty (This was done
according to some intelligence my ex had gathered during her kiln
research). The bisque firing (cone 06) was done on a cool June
Saturday. I started it at 10AM. I keep a keen eye on the kiln for the
first three hours. I didn't leave it out of my sight or sound for more
than 15 minutes. (I was neither confident enough in the work I'd done
nor the general state of the kiln to leave it unattended.) For the
first hour there was lots of sonic activity--switches clicked and
timers hummed but the elements were just a faint crimson colour. Only
after another two hours did the elements really start to look juicy:
deeply saturated and vivid like red lava. By this point I felt better
about the kiln's performance and could grab lunch, roam the garden,
and attend to other Saturday chores. I checked in on the kiln
intermittently. The garage certainly became warming from the radiant
heat, but hardly as hot as I would have expected. The kiln walls were
keeping in the heat--over 2000 degrees Fahrenheit.
The kiln was active until 4PM when the cone reached its melting
temperature, causing the kiln sitter to open the circuit, effectively
"turning off" the kiln. I left the kiln overnight to cool. When I
returned in the morning to lift the lid it was still quite hot! I
carefully took the ceramics out from the first shelf. The second shelf
I had to let cool further, if you can believe that. Touching a few
pieces accumulated some uncomfortable heat on my hands! To my delight,
the ceramics turned out great! Only three pieces showed signs of
cracking, which is a fine margin of error for me. This may have been
avoided by candling the kiln for a few hours, a process that raises
and holds the kiln temperature to just above boiling (this is done in
order to evaporate all of the water from the ceramics before a fire,
thus preventing cracks forming when the clay body expands at different
rates.)
(IMG) A loaded kiln after firing.
(IMG) A row of bisqued ceramics.
(IMG) Bisqued large bowls and smaller mugs.
The full glazing schedule was as follows:
- 10:30AM: Start on "overglaze" setting (elements: 30% on/70% off)
- 11:30AM: Elements didn't look very juicy. Turned it up to ceramic
(50%/50%)
- 12:10PM: Elements looked red hot. Turned it to lowest setting
(30%/70%)
- 12:27PM: Internal temperature measured 335 deg. F.
- 1:00PM: Internal temperature measured 484 deg. F.
- 6:00PM: Cone dropped, firing complete.
Glazing
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(Coming Soon!)