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These are pyrometric cones. The middle cone is perfectly fired. The left is over-fired, the right is under-fired.
First, keep in mind that ceramics does not use temperature to determine when the firing is complete, it uses Cones. Cone (as a unit of measure) is a combination of heat and time. A Cone (a pyrometric cone) is also a physical object which bends when the firing has completed (see image to the right).
With ceramics, you want to turn the kiln off when the appropriate numbered Cone has been reached (bends). Other kiln-fired art, such as glass, enameling and PMC, all use temperatures to control the firing. If you want to learn more about pyrometric cones, see this page
Many years ago, most kiln shipped with only this configuration. There was no automated method for shutting-off the kiln. The person operating the kiln needed to shut it off at the correct time. Now, only a few of the smaller kilns are available with no temperature measuring or control device. They only have an infinite switch, which is a dial you set to specify how often the kilns heating elements are on.
To realistically use a kiln with only these controle for ceramics, you will need some type of add-on measuring device such as an external electronic controller. Or you will need to place a pyrometric cone inside the kiln and watch it through the peep hole to see when to turn the kiln off.
A Kiln-Sitter is a mechanical devise used in ceramics to shut the kiln off at the correct time. A pyrometric cone (small, large, self-supporting) (Orton brand Cones) is placed in the Kiln-Sitter. When the cone has absorbed the proper amount of heat for its rating, it bends. This causes a lever in the kiln sitter to drop, and the Kiln-Sitter will turn the kiln off. It's simple and works well. It was the most common control method until computerized electronic controllers became popular in the late 1990s.
Kiln-Sitter & Timer assembly
Same as above, with the addition of a timer. Timers (or limit timers) are safety devices used as backup to help prevent over-firing of your kiln. They are used in conjunction with Kiln-Sitters because, for various reasons, Kiln-Sitters do not always reliably shutoff. (Sometimes the Kiln-Sitter is not adjusted correctly, the mechanism fails, or the cone falls/bends oddly.)
With the timer, you set it for a time somewhat longer than you expect your firing to take. For example, if you expect your firing to take 6 hours, you might set your timer to 8 hours. The timer will turn the kiln off after 8 hours regardless of the condition of the cone in the kiln sitter.
A Pyrometer is used to measure the temperature inside the kiln. Think of it like a high temperature thermometer. For glass, enameling, and other processes where temperature is the key control of firing, a pyrometer with a temperature read-out is the minimum necessary. Note: Pyrometers are not a good solution for ceramics because you need to know the "heat work"in the kiln (temperature and time) for proper firing. Therefore, cones, Kiln-Sitters or electronic controllers are used instead for ceramics.
Analog pyrometers are relatively inexpensive (about $100 for a good one). They are designed with an indicating needle on a dial for reading the temperature, but this tends to limit your ability to read them accurately. Digital pyrometers are in the $200 range, and have a digital display, so it's much easier to get an accurate pyrometers are in the $200 range, and have a digital display, so it's much easier to get an accurate reading.
A pyrometer doesn't control the kiln in any way. It only tells you the temperature inside the kiln so you know when to turn the heat up or down (using the infinite switches), or when to turn the kiln off. A pyrometer includes a thermocouple which you place through a hole in the kiln brick to access the inside of the kiln. This is what actually measures the temperature.
Electronic Controllers are the ultimate in control. They do it all. They measure the temperature in the kiln, control how fast or slow the kiln fires, and tells the kiln when to turn off. They offer accuracy and repeatability in your firings. They can be used to fire ceramics, glass, PMC and essentially any other kiln process.
12-Key electronic controller panel
Electronic controllers have two modes of operation; Cone Fire and Ramp/Hold.
In Cone Fire mode, you tell the kiln what Cone you want to fire to, whether you want to fire fast, medium, or slow, and the controller does the rest.
In Ramp/Hold mode, you program in specific firing sequences of ramping the temperature up (or down) at specific rates, or holding temperature for specific durations, and the controller does the rest. These program sequences can be stored in the controller and easily retrieved for subsequent firings.
All electronic controllers perform Ramp/Hold firing. Controllers designed for ceramic kilns also perform Cone Fire. Electronic controllers include thermocouples which are placed in the kiln to read the temperature and feed it back to the controller. The controller will display the current temperature inside the kiln. Most large kilns are sold with electronic controllers, but many small kilns are not (the reason being cost).
It is less expensive to purchase an electronic controller pre-installed on a kiln, but external electronic controllers can be added separately afterward. Sometimes this is done to upgrade an existing kiln, or some people have multiple kilns and may purchase a single external controller with the intention of moving it between their kilns.
3-Key electronic controller panel
Electronic controllers are the most common kiln controller sold. They are especially important for glass, and extremely handy and convenient for ceramics.
There are two main types of electronic controllers; 3-Key controllers and 12-Key (Full) controllers. Functionally, they are very similar, having a very similar feature set. However the 12-Key controller will often have some additional nice-to-have features, or will provide quicker access to certain functions direct form the keypad. Also, programming the controller can be more convenient, as you can directly type in numbers as opposed to using the up/down arrow keys.
Most people will want some type of control and/or measuring device on their kiln. If you purchase a kiln with just infinite switches, you probably will already have your own measuring or control device, or will purchase it separately.
Ultimately, for any type of firing, the Electronic Controller is the easiest and most flexible way to fire. If you want to save money by firing more manually, you will usually choose a pyrometer if you are firing anything other than ceramics, or a Kiln-Sitter if you are firing ceramics.
We hope this helps you select the correct controller for your kiln purchase. Any questions, let us know.
|Capabilities of different controllers/equipment|
|Ceramics||Glass||PMC||End firing?||Temp Readout|
|Pyrometric Cone||Yes, but only with observation||No||No||No||No|
|Manual controls/switches||No, requires additional HW/||No, requires additional HW/||No, requires additional HW/||No||No|
|Kiln-Sitter||Yes||No, lacks a temp readout||No, lacks a temp readout||Yes||No|
|Kiln-Sitter with timer||Yes||No, lacks a temp readout||No, lacks a temp readout||Yes||No|
|Pyrometer||No, does not consider time aspect||Yes, but requires operator oversight||Yes, but requires operator oversight||No||Yes|
(Full or 12 Key)