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| Some little oxide/slip test tiles drying ready for the first bisque. |
A few weeks ago I did my first bisque
fire in my new kiln! What a big day. Although it actually it took three days…
DAY ONE:
Packing the kiln wasn’t as easy as it
should have been. If I had to make a complaint about my (otherwise lovely!) new
kiln, it would be the placing of the thermocouple.
The thermocouple is the device that
records the temperature inside the kiln. It sticks out beyond the inside kiln wall
(which is normal) but for some reason it’s been placed quite low down (where
‘logic’ would suggest it should be placed at least a third or half way up).
Well anyway, the really annoying thing is the positioning is in EXACTLY the
most inconvenient place for putting shelves!
Kiln shelves or ‘batts’ are supposed
to be positioned away from the thermocouple – at least 2.5 cm above or below -
because if placed too close they can damage it when they shrink and expand.
Shelves also interfere with the temperature reading because they retain cold
and heat more than their surroundings.
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| Shelf supports and three of the four shelves packed. The offending thermocouple can be seen in the top right photo. |
Now here’s the thing. The shelf
supports I bought as a ‘kiln set’ come in only two sizes: one short and one a
bit taller. They can be stacked on top of each other to get different heights
between shelves. So far so good. I currently have only four shelves (one of which is slightly thinner than the others!) and it was
recommended to me not to exceed four because of the sheer weight of stuff in a
firing. Shelves also have to be placed in a way to give pots enough room 'above their heads' so to speak. Also, for my first bisque I only had enough pots to just fill a kiln:
and most of these were fairly similar heights...
Anyway, long story short and taking
into account all these little variables (not to mention how heavy and awkward
everything is!), let’s just say that Maths, Physics and the Universe were
against me: because WHICHEVER combination I tried I could not get my first
shelf packed without that infuriating thermocouple getting in the way! Either
I had to make a tiny, low shelf at the bottom that could only take flat pieces
(which would leave half the kiln empty above the top shelf) or I had to make a
‘huge’ gap on the bottom shelf that teetered on a long column of supports.
In the end I packed the kiln TWICE in
two totally different ways, eventually plumping for the ‘huge teetering’ design
- even though it made me feel really nervous because of all the weight I had to
stack on top. I can only conclude that manufacturers never use the stuff they
make…
DAY TWO:
I can tell you that I was way too
tired to turn the thing on after all that! So I just closed the lid and decided
to get up first thing next day to do the firing. Being a brand new kiln, it’s
better to kiln-sit a first bisque to see how it behaves; which is why I decided
to fire during the daytime (rather than put the kiln on overnight for a cheaper
electricity rate). You can imagine that most of the day was spent popping in
and out of the ‘kiln room’ to check the temperature and see if I’d programmed
the controller properly.
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| Bungs and temperature on control panel (not long after end of firing). |
At around 500ºC to 600ºC is the usual
time for ‘putting in the bungs’. There are three holes in my kiln: two are
vents and the third is a chimney (which I don’t use). These holes let out the
steam generated from the last remaining bits of water being burnt off from
inside the pots.
My kiln came with two ceramic bungs to
plug up the holes, but I had to make a third one from an old piece of firebrick
to block the chimney vent. I picked up a tip off the internet (or read it
somewhere) that placing a mirror over a vent will help you to check if all the
moisture has gone. Well I did this and I was still getting LOADS of
condensation even after 700ºC.
Maybe this was because one of the
shelves was new and hadn’t been ‘first fired’ yet. Or maybe there was just loads
of moisture in the pots or generally in the kiln room (it had rained forever in
the weeks beforehand). As this was my first bisque I really didn’t want to risk
pots exploding everywhere so I waited until 770ºC when there was absolutely no
steam at all before I put in all the bungs.
For anyone interested, my firing schedule
was as follows:
First Ramp: 100ºC/hour to top temp 500ºC
Second Ramp: 200ºC/hour to top temp
900ºC
Third Ramp: 100ºC/hour to top temp
1000ºC
End
In other words I fired up to 1000ºC
in 8 hours. Started at 7am and ended (everything switched off) by 3pm.
DAY THREE:
I thought I would be nervous,
impatient or over-excited waiting for the kiln to cool. But by the third day I
was pretty blasé about the whole thing: probably because I felt exhausted! Also
I suppose I knew there was nothing I could do about it but wait and see.
I left the kiln to cool for exactly 24 hours: so at 3pm I checked the temperature. It was 60ºC - which
is easily cool enough to risk cracking the kiln! So I opened the lid…
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| Open sesame - top shelf of bisque pots. |
And success! The top shelf looked
perfect. All the little pink pots looked back up at me, all intact, and all
looking like they were supposed to look. There was a bit of a crack in the kiln
lid however and some kiln brick had dusted down onto one of my pots. This may
prove annoying in the future come glaze firing…however, otherwise all looked
well.
I emptied the kiln in stages, letting
each shelf of pots cool for about an hour in-between, as they were still pretty
hot the further down I went. I was also feeling a bit tired and wanted to unload
carefully in case I dropped anything or did my back in leaning over the kiln!
So by the time I had everything out it was getting dark.
I’m happy to say ALL my pots and every
single piece I put in there (58 pieces in total) came out looking and feeling
perfect – no blowouts or breakages at all – which is excellent news. Since then
I’ve been glazing them too and they’ve all been soaking up the glazes properly.
I’ve yet to see the results of a glaze firing, but all in all I’m very happy
with my first bisque. And aside from the ridiculously annoying thermocouple and
that little crack appearing, I’m really pleased with my kiln so far too.
