By John S. Hohenshelt
There has been much discussion regarding the differences between brick and fiber kilns in light of the introduction of bronze and copper clays to the marketplace. This article explains the differences in the insulating materials for kilns and the firing requirements of the different metal clays.
The ceramic fiber kilns were designed originally to fire silver clays. These materials were able to fire in under 30 minutes with excellent results. Paragon’s SC kilns were developed to take advantage of this feature of the materials by using high temperature ceramic fiber with embedded elements. The fiber has very low thermal storage, which means it does not take much heat energy to heat up and stores very little heat energy when fired. This allows more of the heat energy generated to heat the firing chamber and the metal material rather than be wasted heating the walls of the kiln. This also allows the kiln to cool faster so the piece can be fired and cooled quickly. Most firings are now less that 30 minutes for most silver metal clay materials.
Most firebrick kilns could not perform these firings at the same speed as the fiber kilns so the artist could not fire as many projects in the same amount of time. Plus, the firebrick kilns would take longer to cool to a temperature at which the artist can comfortably remove the metal clay. Over the years these SC series kilns have shown their ability to reliably fire hundreds of loads year after year.
The bronze and copper metal clays recently introduced have much longer firing times. Some of the firings are up to ten hours and include long hold times and controlled cooling rates. Fiber kilns with embedded elements are not the best kilns for this application for two reasons. First, the fiber does not store thermal energy as well as insulated firebrick for these long hold times. The storage of thermal energy permits less electricity used and less time with the elements running. Second, heating elements have an expected lifespan based on the amount of time electricity flows through them. The long firings will decrease the number of firings achievable in the kilns so the elements will need to be replaced more often than firing silver clay in the fiber kilns. The fiber kilns use embedded elements, so replacing the elements requires the replacement of the more costly fiber muffle whereas the brick kilns allow the replacement of the relatively inexpensive elements themselves.
Here is the analogy we use to explain this last concept. The silver clay artist can fire 200 times in a year and only have 6,000 minutes or 100 hours (30 min x 200 firings) of firings on the kiln. The bronze clay artist may only fire 100 times but will have 60,000 minutes or 1000 hours of time of the kiln elements. (10 hrs x 60 min x 100 firings). The bronze clay artist ends the year with half the number of firings but with ten times the amount of wear on the elements and the kiln.
This is just like driving a car. If the trip is only 30 miles, the wear on the car is much less than a 600 mile trip. It is not the (trips) number of firings, but the (miles) hours of firing time.
Here is a summary of the recommendations.
The fiber kiln with embedded elements remains the best kiln for firing silver clay. This does not mean fiber kilns cannot be used to fire bronze or copper clays, only that artists should not expect the same number of firings from their fiber kiln once they start firing these new materials.
The brick kilns will be best for firing metal clays with the long firing times. They can fire silver clay materials but they may not fire in as short a time as the fiber kilns. The brick kilns offered by Paragon have been sold by Paragon for over 50 years and have been very durable for many different firing processes, and we expect they will perform as well for these new applications.
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Reprinted from Metalclay Artist magazine, Volume 1, Issue #4.
There has been much discussion regarding the differences between brick and fiber kilns in light of the introduction of bronze and copper clays to the marketplace. This article explains the differences in the insulating materials for kilns and the firing requirements of the different metal clays.
The ceramic fiber kilns were designed originally to fire silver clays. These materials were able to fire in under 30 minutes with excellent results. Paragon’s SC kilns were developed to take advantage of this feature of the materials by using high temperature ceramic fiber with embedded elements. The fiber has very low thermal storage, which means it does not take much heat energy to heat up and stores very little heat energy when fired. This allows more of the heat energy generated to heat the firing chamber and the metal material rather than be wasted heating the walls of the kiln. This also allows the kiln to cool faster so the piece can be fired and cooled quickly. Most firings are now less that 30 minutes for most silver metal clay materials.
Most firebrick kilns could not perform these firings at the same speed as the fiber kilns so the artist could not fire as many projects in the same amount of time. Plus, the firebrick kilns would take longer to cool to a temperature at which the artist can comfortably remove the metal clay. Over the years these SC series kilns have shown their ability to reliably fire hundreds of loads year after year.
The bronze and copper metal clays recently introduced have much longer firing times. Some of the firings are up to ten hours and include long hold times and controlled cooling rates. Fiber kilns with embedded elements are not the best kilns for this application for two reasons. First, the fiber does not store thermal energy as well as insulated firebrick for these long hold times. The storage of thermal energy permits less electricity used and less time with the elements running. Second, heating elements have an expected lifespan based on the amount of time electricity flows through them. The long firings will decrease the number of firings achievable in the kilns so the elements will need to be replaced more often than firing silver clay in the fiber kilns. The fiber kilns use embedded elements, so replacing the elements requires the replacement of the more costly fiber muffle whereas the brick kilns allow the replacement of the relatively inexpensive elements themselves.
Here is the analogy we use to explain this last concept. The silver clay artist can fire 200 times in a year and only have 6,000 minutes or 100 hours (30 min x 200 firings) of firings on the kiln. The bronze clay artist may only fire 100 times but will have 60,000 minutes or 1000 hours of time of the kiln elements. (10 hrs x 60 min x 100 firings). The bronze clay artist ends the year with half the number of firings but with ten times the amount of wear on the elements and the kiln.
This is just like driving a car. If the trip is only 30 miles, the wear on the car is much less than a 600 mile trip. It is not the (trips) number of firings, but the (miles) hours of firing time.
Here is a summary of the recommendations.
The fiber kiln with embedded elements remains the best kiln for firing silver clay. This does not mean fiber kilns cannot be used to fire bronze or copper clays, only that artists should not expect the same number of firings from their fiber kiln once they start firing these new materials.
The brick kilns will be best for firing metal clays with the long firing times. They can fire silver clay materials but they may not fire in as short a time as the fiber kilns. The brick kilns offered by Paragon have been sold by Paragon for over 50 years and have been very durable for many different firing processes, and we expect they will perform as well for these new applications.
---------------
Reprinted from Metalclay Artist magazine, Volume 1, Issue #4.
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