Calvin's Maiden Voyage: Firing the 50+ year old kiln
Well the day has come! We fire Calvin Kiln, their maiden voyage in the Muddy Taurus studio. What a strange day. By that I mean, wonderful, scary, exciting, close monitoring, lots of alarms and easing the concerns brought up by my mom.
Down to business, how did it go Lauren?? Well, it went alright. It was pretty smooth sailing for the voyage at first, but not the outcome I was hoping for. I started by loading in some test pieces when I got home from the gym and started her up at 11:00 am. No breakers were tripped, nothing caught on fire and I was able to binge Gilmore Girls as I (like any new mom) kept checking on Cal out in the garage. I had some coffee, I trimmed some work in the morning, it was pretty peaceful actually! I used some self supporting cones about half way down in the kiln, but I didn’t get the placement quite right through a peep in the kiln-something I’ll have to work on- so this made monitoring the temperature risky business as I couldn’t get a view of them. I also need to add, I didn’t have a digital pyrometer to monitor the temperature-something I regret not having for the first firing, but I kept moving making my adjustments throughout the day.
For anyone needing a run down of how manual kilns work, it is essentially the person doing all the work; on Cal, there are three (red in this picture) switch boxes that house the wires connecting to the elements, the middle switch box is the "Master Switch Box" that holds the kiln sitter/tube assembly. All the switch boxes have knobs on the left side with 4 settings: off, low, medium & high. So, let's say I'm just turning on the kiln, I'll take out the top peep hole plug (these are the white conical shaped insulators-they allow us to look inside the kiln without opening the lid and letting out a ton of heat) and prop the lid for a little ventilation-letting out steam, if any. I turn all the boxes to low and let that warm up for 2-3hrs. Then come back, turn the knobs to medium, then high, etc. until we reach the desired temperature.
So, I did all of this, I was working from a pretty common firing schedule and I was expecting the kiln to turn off around 7, maybe even 8 o'clock the latest. Finally around 10:00 at night, I started to worry big time. This was just supposed to be a bisque temp after all… the max temp I was aiming for was about 1850, so a 11 hr firing seemed way too long with brand new elements. I went with my gut and manually turned the kiln off. I dropped the falling weight and turned all my knobs to medium for 2 hrs-just so we wouldnt get a thermal shock on the test pieces. I shut everything off and I finally went to bed around midnight, anxious to see what had really happened in the morning.
So, 9 am rolls around and the kiln is still warm, but I put on my gloves and opened the lid. 100% over fired... but why? I could tell from my cone 5 clay bubbling and blistering, my cone 6 terra-cotta was black (it's vitrified color) and my witness cones had melted into a puddle. Feeling a little defeated I gave it a couple days and came back with some possible suspects.
After some questioning, it was the rod within the tube assembly-this holds the pyrometric bar-so if the rod is sticking and the bar does drop when the kiln reaches temperature designated by the bar (^04), the rod still sticks unfortunately, misfiring the kiln. It was sticking to the side of the tube-I was able to fix this by adjusting the face plate on the outside of the control box. I can now move the rod freely without sticking. The bar I had in there did melt over the new tube assembly, but that is okay-it should still work as intended.
So I fixed that, ordered a digital pyrometer for about $150 - hoping the next firing this week goes smoother. I'll be tracking her progress with a kiln firing log once again to make sure all is going well.
If you’ve been following this journey (um wow thank you!) you know first hand this experience has been a bit long but very informative! After replacing the bricks, the tube assembly, removing old elements & putting in new ones, creating a diy rolling kiln stand, and attaching a new lid brace, it started to feel like I’d never get this damn kiln firing! It was 10 weeks of working and waiting for packages filled with new (and corrected) parts to arrive. While tedious, I am so SO happy I've been able to work on this kiln. I mean she’s become my bff! Helping her reach her full potential and what a ride this has been so far! So, what’s next for Lauren and Cal? Is this the end?? The simple answer is absolutely not. Between my shenanigans and this 50 year old kiln, I’m sure there will be other projects.
Our next project (when? to be determined) will be replacing the receptacle installed by our electrician for the proper one. Yup the power cord attached to Cal is wrong! It gets the job done, but it does not efficiently support the wattage of this kiln, so it’ll have to go. No shade to whoever installed it-but I wanna make this as safe as possible, no cheap shortcuts! The new power cord is in my possession, we now await our noble electrician to make his honorable expedition to the garage. Until then, she’ll run fine. Next firing, we're trying another bisque this time with good ammunition, but in the meantime, let's get muddy.