I just put the first hand-pressed clay pressing of the Art Deco panel D5 into the kiln about 5 minutes ago, here it is before closing the lid:
I adjusted the kiln firing schedule for “User 4” a little from the previous test firing, I kept the same 5 segment program and holding for 9 hours @ 200º F, but since I want to fire these at a higher temperature- 129º F than I did on the tests I needed to adjust the ramps a bit. Here is what I came up with for this firing on this sculpture, we’ll see how it works:
- R1: 80º/H to 200º HOLD for 9 hours @ 200º
- R2: 60º/H to 1200º
- R3: 90º/H to 1700º
- R4: 80º/H to 1950º
- R5: 60º/H to 2079º
At the end of ramp 5 and reaching 2079º it has a 10 minute hold to let that heat do it’s work and soak in, much like baking a cake the heat has to get all the way into the center otherwise only the outside is “done” and the inside is not yet at the set final temperature.
2079º is what we would consider cone 0 (zero) if they made one, they make cone 01 and cone 1 so the temperature I found seems to have the best color red in this clay that I like would be between those two cones.
They are properly called “pyrometric cones” and they are little more than a slightly offset pyramidial shaped piece of clay that bends when the heat range it’s made for is reached, it doesn’t measure temperature but it visually shows thta a certain temperature was reached by how far over it bends.
They are made in about 40 heat ranges, from 022 (1087º) coolest, usually used for decals and glazes, all the way up to at least cone 14 (2523º) which is the hottest, used for porcellains and high fire clay. 2523º is about 600º hotter than it takes to melt copper, it’s hot enough to melt aluminum, lead, tin, copper, and it’s more than hot enough to melt cast-iron!
Here’s an illustration of cones and how they are often used:
Usually used in groups of three, one shows the temperature definitely reached it’s temperature and exceeded it, the center one bends over as shown and that’s just about perfect for showing it reached the desired final temperature without going over it, if the temperature had gone higher than desired (due to a malfunction or miscalibration etc) the guard cone would have started to bend too.
These remarkably simple devices were invented in the late 1700s and are extremely accurate, albeit how far they bend over depends on proper level placement in the kiln, and how the operator interprets how far is “far.”
I needed to calculate how many hours it will take the kiln to go through the program and shut off, last time with the slightly different schedule it took 36 hours and 39 minutes, now it looks to be 38-1/2 hours give or take a few minutes. It also takes about a full day to cool down enough to open the lid and remove either the shattered remains, or a nicely fired sculpture.