A pleasant surprise
Jul. 30th, 2019 10:18 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
offcntrI've been super happy with the glaze kiln since we installed gas pressure gauges on all the burners last winter, even happier since I spent a little time with a hammer and stake, banging the brick tighter together on the door, door-sill and chimney. I've working out a firing regimen that allows me to light the kiln between 8:30 and 9 pm, come in again at 5:30 am to turn up air and gas, and have body reduction at 6. Afterwards, I can fire with minimal adjustments right up to cone 10, which has been happening within 20 minutes of 6 pm, plus or minus.
This last firing, I had an even better surprise: no oxidation at all, anywhere in the kiln. The closest was in one toddler bowl, down near the front right corner, that was neutral to slightly reduced. One bowl. Also, I didn't really have any over-reduction either. In the past, I've had pots come out so brown that the image doesn't show up. I have toasty brown rims, but lovely warm cream-with-iron-speckle everywhere else.
I only did one thing different, as far as I can tell. I clamped the door shut immediately before body reduction, rather than after. No real reason; just wanted to get that step done so I didn't forget.
Our car kiln door is basically a stacked wall of brick, theoretically held in place by a channel iron across the top, anchored to the bottom with tie rods and bolts. Automotive valve springs keep tension on the rods, compressing as the brick as heats up and expands, springing back as it cools. Except they don't anymore, really. The coils no longer expand, so in practice, there's about a quarter inch between the top of the brick and the channel iron, which makes it very scary pushing the door closed, trying not to tip the whole wall of brick over. Once the kiln has heated up, everything's tight again, which makes it a good time to fasten bar clamps to the top of the channel iron. The other end is anchored to steel framing at the back of the kiln, so tightening the clamps pulls the door tight against the arch, keeps heat expansion from opening gaps.
When we started using the clamps, I didn't want to tighten them on a cold kiln, because I figured the roof bricks would start to break, trying to expand with no room to do so. I also didn't want to wait too long, because gap on the top of the door, so I chose right after body reduction as a reasonable compromise.
Looks like I should have chosen right before. I'm definitely gonna try this again, next time.
This last firing, I had an even better surprise: no oxidation at all, anywhere in the kiln. The closest was in one toddler bowl, down near the front right corner, that was neutral to slightly reduced. One bowl. Also, I didn't really have any over-reduction either. In the past, I've had pots come out so brown that the image doesn't show up. I have toasty brown rims, but lovely warm cream-with-iron-speckle everywhere else.
I only did one thing different, as far as I can tell. I clamped the door shut immediately before body reduction, rather than after. No real reason; just wanted to get that step done so I didn't forget.
Our car kiln door is basically a stacked wall of brick, theoretically held in place by a channel iron across the top, anchored to the bottom with tie rods and bolts. Automotive valve springs keep tension on the rods, compressing as the brick as heats up and expands, springing back as it cools. Except they don't anymore, really. The coils no longer expand, so in practice, there's about a quarter inch between the top of the brick and the channel iron, which makes it very scary pushing the door closed, trying not to tip the whole wall of brick over. Once the kiln has heated up, everything's tight again, which makes it a good time to fasten bar clamps to the top of the channel iron. The other end is anchored to steel framing at the back of the kiln, so tightening the clamps pulls the door tight against the arch, keeps heat expansion from opening gaps.
When we started using the clamps, I didn't want to tighten them on a cold kiln, because I figured the roof bricks would start to break, trying to expand with no room to do so. I also didn't want to wait too long, because gap on the top of the door, so I chose right after body reduction as a reasonable compromise.
Looks like I should have chosen right before. I'm definitely gonna try this again, next time.
no subject
Date: 2019-07-31 12:31 pm (UTC)no subject
Date: 2019-07-31 02:22 pm (UTC)a local association
Date: 2019-08-02 04:24 pm (UTC)Re: a local association
Date: 2019-08-06 06:04 am (UTC)