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FAQ

Cones

Frequently asked Questions. (information from Orton Foundation)

I have never used cones before, what cone should I use?
How do you use cones?
What do you the terms heating rate and soak mean?
What temperature did my cone fire to?
I have cones that are really old, can I still use them?
Is the cone effected by a change in the kiln atmosphere?
How do you measure a cone?

Question
I have never used cones before, what cone should I use?

Answer
To determine what cone to use we must first know what type of product you wish to fire in your kiln. Refer to the clay or glaze manufacturers label to see what cone value they assigned to their product. They have already determined, through testing, what cone will deform and bend over when the glaze or clay is at maturity. An example could be a stoneware clay and glaze rated to mature at cone 6. We would recommend the cones 5,6,and 7.

Question
How do you use cones?

Answer
Orton manufactures four different types of cones. The small cone and bar are mainly used in the kiln shutoff device called the Kilnsitter. This is a mechanical device that shuts off the kiln when the temperature inside is sufficient to cause the cone to deform under the weight of the Kilnsitter rod. The Large and Self-supporting cones are made to place on the shelf next to your ware. They indicate whether the ware received an adequate amount of heatwork to properly mature the clay or glaze. A properly fired cone will bend over with the tip of the cone almost touching the shelf. After firing, simply measure the degree of bending with the Orton measuring template to convert the bending angle to a temperature.

Question
What do you the terms heating rate and soak mean?

Answer
The heating rate refers to the rise in temperature of your kiln for every hour it is firing. If a kiln takes three hours to get to a temperature of 900 F, then it would have a heating rate of 300 F per hour. It is important to know the heating rate since it determines the temperature at which a cone will deform.

The term “Soak” means that you hold the kiln at a specific temperature for a period of time. The practice of soaking a kiln is done to help equalize the temperature throughout the kiln or produce a desired effect in the firing.

Question
What temperature did my cone fire to?

Answer
In order to find out the temperature from a cone, you must know the heating rate during the last 200 degrees F rise in temperature of your kiln firing and the degree of bending in the cone. We refer to the degree of bending as the bending angle. The bending angle can be determined by using the Orton measuring template. Then, based on the heating rate and bending angle, we can look up the equivalent temperature of the cone on the Orton cone chart (attach link). For example, if firing to cone 06 with a heating rate of 270 F/hr and a bending angle of 90 degrees, the temperature is found to be 1855 F.

Question
I have cones that are really old, can I still use them?

Answer
Yes, if the cone is in good condition and was stored in a dry area it can be used. Orton has test fired cones that were made over 50 years ago without seeing any change in the fired results.

Question
Is the cone effected by a change in the kiln atmosphere?

Answer
Yes, cones perform best in air atmospheres that are oxidizing. If a cone is exposed to a reducing atmosphere, it will look considerably different then one fired in an oxidizing atmosphere. This is a valuable tool for monitoring the air quality in your kiln. Cones are more sensitive to atmosphere changes than most fired ware, therefore, they can serve as early warning signs that something has changed in the kiln and needs attention. For example, if a gas burner falls out of ratio a cone will indicate what area of the kiln was effected and help pinpoint the problem burner.

Cones can still be used in reducing environments to measure temperature uniformity and reproducibility. However, the ability to convert the bending angle to a temperature will change since the charts are based on oxidizing atmospheres.

Question
How do you measure a cone?

Answer
A cone is measured according to the degree in which the tip of the cone has deformed and bent over toward its base or the shelf. Orton cones are designed so that they will bend in the same direction if properly placed in the kiln. Once the cone is fired and removed from the kiln, the user can use the Orton measuring template to convert the bending angle to a temperature.