You know that pottery and ceramic producers use kilns to heat their products and harden them through certain physical and chemical reactions. But you’ve also heard about kiln sitters and may wonder how they are used.
A kiln sitter is a control box that regulates the firing of a manual pottery kiln using small pyrometric cones. When the kiln reaches a specified temperature, the cone in the kiln sitter will bend. This process leads to the dropping of a lever that switches off the kiln.
Keep reading to learn more about Kiln Sitters. We’ll take a closer look at how to control a Kiln’s temperature and how a Kiln Sitter functions.
What Does a Kiln Sitter Do?
Kiln sitters are mechanical devices that ensure a kiln turns off at the right time and temperature. You have to know the temperature inside the kiln and the exact timing, which is called “heat work.”
If you don’t have a digital controller, a kiln sitter works as a timer for you. Its function is straightforward. You have to place a pyrometric cone inside the kiln sitter, where the cone is propped onto two metal prongs extending inside the kiln sitter.
A sensing rod rests on the Small Pyrometric Cone and extends to the outside of the kiln, where a weighted latching mechanism is in place. The sensing rod can go up and down, allowing the latching mechanism to activate or deactivate.
Once the pyrometric cone inside the kiln reaches the target temperature, it gets soft, and the weight of the metal rod causes the cone to bend. While the rod goes down inside the kiln, the claw holding the latch goes up and releases the latching mechanism. This process results in the kiln shut off.
Manual vs. Automatic (Digital) Kiln Sitters
Generally speaking, there are two types of kiln controllers: manual and digital. Each one has its benefits and drawbacks. Let’s take a look at them briefly.
Manual kiln sitters let you adjust the kiln’s temperature according to your own preferences. They’re relatively cheap, easy to use, and can keep you informed throughout the entire process. So, you’ll have hands-on experience during the firing of the kiln.
However, the constant attention required to track the temperature changes and repeating or adjusting the program for future projects is a big downside to these controllers. Also, the results may be inconsistent because they rely on humans.
This type of kiln controller automatically controls the temperature. And their most significant advantage is that they let you choose your desired firing program with a click of a button. Once you input a program, there’s no need to recreate it or be constantly present.
These controllers are more reliable and do much of the work for you. Besides, you can add more complex programs for glassmakers.
As for the downsides, digital controllers can be difficult to work with at first, depending on the controller you get. You would still need to use pyrometric (witness) cones to make sure your controller and thermocouple are working properly.
How To Adjust a Kiln Sitter
Usually, factories adjust kiln sitters, but they may jar out of their initial adjustment during the delivery. Before using it, make sure it’s properly adjusted.
To check your kiln sitter, consider the following:
- Turn off all the switches and install the firing gauge. Typically, it should be in place when delivered from the factory, and a note to remove it before firing the kiln.
- Check the release claw and weight trigger. When the firing gauge is in place, swing the weight and pull the claw.
- Check for a 1/16th inch (0.16 cm) clearance between the inside tip of the claw and the face of the trigger. When the weight swings toward the front, the trigger shouldn’t touch the tip of the claw.
- You can also loosen the set screw in front of the weight to lower or raise the trigger as needed. Make sure to tighten the set screw firmly since the falling weight’s repetition may cause the trigger to go out of adjustment.
- Check the sensing rod. Make sure it can move freely vertically inside the tube cavity without touching the sides at any point.
How To Operate a Kiln Sitter
To operate the kiln sitter:
- Lift the weight and ensure the claw holds it.
- With your hand on the claw, reach out with the other hand and put a proper cone in the kiln sitter.
- Release the claw, set the timer, and press in the plunger to start the counting.
Where you place the sensing rod on the Small Pyrometric Cone is very important to have a successful firing session. If you place it on the thin edge of the cone, the kiln will shut off sooner. But if you put the rod on the thick edge, the firing lasts longer, and the kiln shuts off later. You can also get Pyrometric Mini Bars. After you set the kiln sitter, first turn your switches to low. Two hours later, turn it to medium, and again after two hours, turn it to high.
Here’s a helpful video on how to operate a kiln sitter in more detail:
When you operate a kiln, you need to take safety seriously. Make sure you follow these tips:
- Don’t get close to the kiln while it’s firing, especially near the end of the process when you want to make sure it shuts off on schedule. If you need to be near the kiln while it’s on or cooling, Wear Gloves to avoid hurting yourself.
- Make sure the kiln is off when you open the lid. Sometimes, you may think it’s off while it’s still cycling (especially in preheating or the so-called candling). The elements can burn you and even electrocute you!
- Remember to wear Dark Glasses with UV protection when looking into the kilns peephole.
- Never leave a kiln alone altogether and trust it to shut off on its own. Stay there, especially near the end of the firing, to ensure the sitter falls and turns the kiln off. You can also set the alarm to remind you to check the cones and sitter.
For more detailed safety information check out Kiln Safety.
More Tips on Working With a Kiln Sitter
- Pyrometric cone. It’s a particular type of clay composed of measurable, predictable materials created to melt at various temperatures. Ensure that you’ve placed the Small Pyrometric Cone correctly on the supports to prevent undesired results.
- Evenness. A kiln sitter works by gravity (falling weight activates the latching mechanism), so it needs to be level. Before starting any firing session, make sure of it.
- Calibration. A kiln sitter can drift, and you have to calibrate it periodically.
- Firing log. Usually, you may find that you need to put a slightly higher cone number in the kiln sitter to get to the desired temperature. So, you need to experiment with the cones and firing of your kiln. Having a firing log will help you significantly.
- Turning off. Remember that a kiln sitter doesn’t help you turn up the kiln. It just helps in turning the kiln off.
- Kiln wash. Dab a little kiln wash on the top of new cone supports. It’s highly effective in reducing the chance of a cone sticking to the new metal (this may cause the kiln to over or under fire).
Kiln sitters’ parts are durable, and you don’t need to replace them unless they’re broken. But like any equipment, some of their parts depreciate over time and need some maintenance.
The metal parts of the sitter inside the kiln sensing rod and the cone supports are usually the main components that need to be replaced after many firing sessions. That’s because they’re exposed to very high temperatures, which leaves them oxidized, thin, and worn out.
The tube assembly that the sensing rod passes through is made of porcelain and may crack or break, so you may need to replace it too.
If you intend to replace the kiln sitter parts on your own, we strongly recommend you take photos and notes while removing the old parts and reversing the same steps to install the new ones.
A kiln sitter is a worldwide and reliable way of shutting down the kiln and creating beautiful pottery. They’re easy to use and keep you informed about the heating process. However, they need some adjustments, calibration, and maintenance to function properly.
Read their manuals for the right adjustment and repeat it after every 30 firings. If you find out that the cone is bent to more or less than a 90° angle, calibrate it for more accuracy. Keep making that beautiful Pottery!