You Can Do It!
By firing a manual, you can get to know your kiln, better understand the firing process, and even manipulate the work by making changes to the firing schedule. This is good practice, especially for beginners learning the firing process and techniques. When firing out work in a kiln, I believe you need to be there through the whole process as it’s like giving birth. It is pretty simple, but it just takes a bit of monitoring and seeing the correct cones inside the kiln when it is hot and knowing when to shut the kiln off or start the warm down.
The Sermon
Even though many kilns are digital or use a cone sitter, I am a hardcore manual kiln fire guy. This means I fire all my kilns, even bisque fire, with shelf cones. Now I will not preach at you like a baptist minister if you choose to fire a digital shut-off or use a sitter, but in my opinion, you depend on luck to shut down each load. Mistakes like putting in the wrong cone number, wrong hold time, improper sitter set up, improper cone set up in the sitter, or the sitter cone melting strangely and not shutting down all can cause a kiln to overfire. I witnessed a kiln meltdown when I was a young warthog and ever since fired manually. Kilns can be like children playing in a sandbox next to the road. Mostly, they will be fine, but if you forget to check on them in no time, they will be out playing in traffic. You do not want your kiln to be out playing in traffic, and forgetting your kiln could result in a meltdown where all the work shelves and posts become like taffy stuck in there. If you do a google search for kiln meltdown, you will see some amazing images of things that happened when folks had a bad time with their kilns. Even if monitoring it, you will still have a bad time with your kiln, but those bad times will be less painful, and disaster will be averted by taking corrective action. Amen.
Proper Setup
It depends on what types of shelf cones you have. Cones measure both temperature and work heat. If you use a pyrometer to check your kiln, you will only know the temperature. Pyrometers do not measure work heat. Some shelf cones need to be placed in a cone pack, while others are self-standing. I like to use self-standing cones in the peepholes and place them on a small piece of kiln shelf or post. When placing them in the cone pack, research the cone manufacturer’s recommended angle. I set the cone almost to the edge of the shelf so they are easy to see inside when things heat up, and it all looks the same color. You might be able to make out just a slight outline at high temperatures. Some say not to place it near posts or elements, but I like it right out in front. Be sure your cone will not attach itself to a pot when it bends; cones like personal space.
Looking in There
It might be hard to see the cone when things heat up hotter than a goat’s butt in a pepper patch. When you look in there, it is best to use welding glasses as you do not want to damage your eyes over the long run. Also, if firing with gas, pull the plug and wait a bit as if the kiln is in reduction; you may have flames shooting out the peephole. So when you look in, be aware of that flame, or you can lose eyebrows or catch your good flannel shirt on fire. Now look in there real slow and find the outline. I try and place the cones in front of a pot to see it better. Another technique is to shine a flashlight and have the light reflect off the cone. You can also blow into the hole to slightly cool the cone to see the outline. If unsure and could not see it, I shut down the kiln to be more certain than restarting.
Reading the Cone
Be sure to look at the chart put out by the cone manufacturer. Orton has a free chart that you can download here.
Also, be sure to check the cone manufacture bend chart. You can see an example here.
Checking the Kiln
Each kiln is different, But here is the schedule I use for both bisque and glaze fire to cone 5/6 when firing manual.
Hours 1 & 2 – Check each hour
Hours 3&4 – Check each 30 min
Hour 5 to Cone Drop – Check every 15 min
Below are some examples and tips on what the cone will look like inside the kiln and suggestions on when you might want to shut it down.
When to Shut It Down
Each kiln is different, and the rate of the cone drop will change based on temperature and work heat.
If you have the cone that matches the firing, say a cone five shelf cones, and you want a cone five firing, you want to shut it down at the slight bend.
Below is what a slight bend looks like based on Orton’s recommended bend chart.
I go to the half-bend for most of my firings. By going to the half bend, you can adequately bring to temperature shelves that may be running a bit cooler slightly.
A half bend for a cone 5.5 firing will look like this:
If you have a cone five shelf cones and would like a cone six firing, you would do a full cone bend. It will look like this:
It will look like this:
If you missed a check because you fell asleep or the cows got out, you could still tell about how much time you missed, as you will have challenging full bends and soft full bends. With a soft full bend, the cone will look like melted chocolate but be blistered and bubbled out, not a puddle. It will look a bit like below. Here I was out of cone six but used a cone 5 plus 30 min to reach cone 7 for a bottom shelf. So I intentionally overfired to bring a cone seven glaze test on a bottom shelf to temp.
All the checks might seem excessive, but they help to catch mistakes early and allow you to make corrections. In my gas kilns, I can see if the kiln is heating correctly and if the firing is going too slow or fast based on color. Also, when testing firing techniques or a new shelf configuration, how big or small the load is or doing holds. All the checks paid off and saved loads, and prevented overfires. I have overfired, but only from falling asleep and missing the last 15 min. Thank goodness my wife woke me, and I only lost one shelf of pots to blistering. You can also check the cone that did not bend to get an idea of how much off you were on the under fire. For example, a cone that did not bend at all might be like glass and have gloss saying it was close to reaching temperature.
See the video below of a shelf cone melting in my raku kiln. In this example below, the cone is melting much faster than it might in a larger kiln with a much slower climb and firing schedule, but I wanted to show this video as an example of what they look like as the shelf cone bends from the work heat.
Do you fire digital or manual? Do you have any questions about firing manual? Let me know!
Al Wayman
Artist/ Owner
Creek Road Pottery LLC
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Hi Al.
Thanks for your informative blog! I have a couple of questions about manual kilns which I hope you can help me with.
This spring I acquired an old small Jenkin kiln with a kiln sitter (I installed new coils) which was probably designed to fire porcelain back when doll making was popular. I’m using it to fire bonsai pots to cone 6. I’m noticing a wide difference in the time it takes to shut off during different firings. Sometimes it takes over 7 hours to reach cone 6… then the next firing shut-off occurs in 5 hours! Is this normal? The results are fine… I don’t see any over or under-firing occurring, but I’m kind of baffled. I try to fill the kiln for each firing.
My second question has to do with slow cooling. Is there any trick to slow cooling a manual kiln? After shut-off I’ve tried resetting to medium for 5 hours, but I my slow-cool coyote glazes aren’t reacting at all.
Any help is greatly appreciated!
best,
Ann L
Greetings, thanks so much for your question! There are many variables on why a kiln may shut off sooner of later but since your kiln is older I would safely de-energize your kiln and take a look in the control box and check the relay and element connection to make sure things are tight ( but not over tight) and that there are no issues of corrosion or connection issues. Then in a dark room, turn the kiln on low and see if all the elements heat up evenly. On slow cooling there are schedules you can follow. I have one with even the gas kiln. I have linked below some articles on slow cooling that may help you out. At time potter’s will come up with their own cooling schedules. Here is the Steven Hill slow cool firing schedule. Here is the Plainsman Cone 6 Slow Cool schedule. Also Jon the Potter had a video up about the topic. Here starting at 7:00 in the video he mentions how he will do this and shows the results. Also, here is a post on Slow Cooling from the Ceramic Network. If you would like to go full manual, you can turn the kiln back on and find out though trial and error by put a cone 7 in the sitter. When your cone 6 shelf cone is down, turn switches back a bit for a hold. After 15 minutes, turn switches off until your pyrometer temperature is where you want. Turn switches on medium or depending on what the pyrometer does. Another technique I have seen to manual slow cool is wait 15 minutes after the sitter drops and turns the kiln off, then turn it back on and flip all switches to medium for an hour to an hour and a half, then to low for an hour to an hour and a half. So it’s all quite random and allows you the opportunity to create your own slow cool schedule. But remember a Pyrometer don’t measure heat work only temperature so be sure to watch your self cones as holds, at times, could cause you to over fire a bit. I hope this helps!