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Firing at the Right Temperature
Firing at the Right Temperature
In elementary schools with low-fire clays, most bisque firings are run at Cone 04 with glaze firings run at Cone 06. The glaze firing should be slightly cooler than the bisque firing so that the glaze fits the clay body better and to help prevent particles (ex. carbon) from emerging out of the clay and causing the glaze to blister. So, glaze firings at the elementary school level are usually at Cone 06.
https://bigceramicstore.com/pages/info-ceramics-tips-tip39_chose_bisque_temperature
FiringTemperatures.pdfRunning the Kiln
Running the Kiln
When to Place the Pyrometric Cone in the Kiln Sitter: If running a full load, it is a good idea to place the pyrometric cone in the kiln sitter after loading only the bottom shelf and first layer of projects rather than after you have finished loading the entire kiln. This will make it easier for you (give your hands more space and allow you to see better what you are doing) to carefully position the cone in the middle of the bottom bars.
Leave Space Around the Kiln Sitter: Since the kiln sitter is responsible for holding the pyrometric cone which bends when the internal temperature of the kiln reaches the appropriate cone, at which point the kiln sitter drops and trips or shuts off the kiln, be sure to leave a couple of inches clearance around the kiln sitter. Do not place the kiln shelf at the exact same level as the kiln sitter and be careful that projects are not touching or in the way of the kiln sitter as this can impact its ability to function properly and result in a dangerous situation.
Peep Holes: Keep top peep hole unplugged for the entire firing. This will add years of life to the Kiln-Sitter tube assembly. On large kilns and during the beginning of the firing, it is a good idea to remove the bottom peephole plug, as well.
Leave Space Around the Pyrometer: As the pyrometer reads the internal temperature of the kiln, be sure to leave a couple inches clearance around it. For instance, ceramic pieces should not be too close and the kiln shelf should NOT be level with the pyrometer or right above or below it or else the temperature may not read properly.
Running Waverley Kiln.mp4How to Run a Manual Cone Sitter Kiln
How to Run a Manual Cone Sitter Kiln
Candling!
Candling!
Running the kiln on low between 180 - 200 degrees Fahrenheit, while greenware pieces are loaded in the kiln, BEFORE bisque firing.
What: Candling is a process of running the kiln at a low temperature to remove water from clay pieces before a bisque fire.
Candling Temperature: Candling is done at temperatures between 180 and 200 degrees Fahrenheit, with the ideal candling temperature being 180 degrees Fahrenheit.
Critical Temperature: The candling temperature should be low enough to provide a buffer below the boiling point of water (212 degrees Fahrenheit), as at the boiling point of water, a clay piece with moisture left inside can explode.
Why: Candling can help remove excess moisture from clay projects before bisque firing. Sometimes, no matter how long a clay piece is sitting out to dry, the ambient moisture in the environment can be enough moisture to cause cracking and, sometimes, explosions, if the piece is heated up too quickly during the bisque firing. As such, it is a good idea to candle a load of greenware before bisque firing and/or to ramp up the kiln slowly, especially if the pieces are thick.
Bisque Firing
Bisque Firing
In elementary school, most bisque firings are run at Cone 06 with glaze firings run at Cone 05 or Cone 04.
Bisque Firing Basics: In a bisque firing, greenware pieces, like those above, can be touching without damage to the pieces. However, use great caution when handling and loading the pieces, as they are their most fragile at if the pieces are not too delicate or detailed. When bisque firing, it is okay to stack pieces as long as thicker and more durable pieces are used for the base layer with thinner and more delicate pieces placed on top. Do keep in mind that pieces will shrink during during the bisque firing. Thus, stacking greenware pieces which barely fit over or on another piece, is cautioned against. However, to ensure pieces with lids fit together properly, vessels should be fired with the lids on top (just be sure that the bottom and top are free of each other prior to firing as they can become stuck together during drying if a piece of plastic or paper is not used in between. Also, it is okay to nest smaller objects inside of similar objects that are larger.
Color Change in Bisque Firing: Once fired, the clay body changes color slightly. For instance, gray earthenware clay usually turns a bright white, as seen in these bisque fired pieces.
Aluminum Silicate to Allow Movement in Shrinkage: Covering the kiln shelf with aluminum silicate powder can allow larger clay projects (especially those with a large base like a tile) to more easily move or shift during the shrinking process to help prevent cracks or breaks.
Glaze Firing
Glaze Firing
Glaze firings at the elementary school level are usually run to Cone 06.
Dry Footing: Before glaze firing, be sure to dry foot the piece, by taking a damp washcloth or sponge and wiping off all surfaces on the piece that will come into contact with the kiln shelf.
Ceramic or Metal Kiln Stilts can be used underneath smaller projects during glaze firing as an extra precaution that glaze does not run off onto the kiln shelf. Metal stilts are especially useful when firing glazed projects which are not dry footed so that the glaze can cover all surfaces of a project (ex. an ornament desired to be glazed on all sized). The metal stilt can be easily pulled off of the glazed piece after firing is complete with little to no damage to the piece (other than a few pin sized rough or unglazed spots.
Glaze Firing Basics: Unlike in a bisque firing, when glaze firing, be sure to leave a finger space in between all pieces so that they do not fuse together in the firing.
Kiln Wash: To protect your kiln shelves, it is a good idea to cover the kiln shelf with kiln wash. This can help reduce the amount of glaze that sticks to the shelf in the event that the glaze would run off of the piece.
Did your Kiln fire to the correct temperature?
Did your Kiln fire to the correct temperature?
Glaze firings at the elementary school level are usually run to Cone 06.
The small pyrometric cone should bend to about a 90 degree angle as shown in middle picture below.
Using Witness Cones in Your Kiln is RECOMMENDED: Witness cones help to check the accuracy of the kiln firings, help to verify that the cone sitter sensing rod is properly calibrated, and also enable you to peer into the kiln's peep hole (while wearing special eye protection). These cones are much larger than the small pyrometric cones places into the kiln sitter. They are used in addition to the pyrometric cone in the kiln sitter and can be placed on the kiln shelf. Using multiple witness cones throughout the kiln can also be helpful to see if the kiln is firing at even temperatures throughout the kiln which could impact firing results.)
Self-Supporting Witness Cones are the easiest and should not be placed directly on the Kiln shelf (unless the shelf has kiln wash on it) otherwise the cone can stick to the shelf. Using a high fired unglazed tile or a small, flat bisqued ceramic cookie (1/4" thick) are great alternative surfaces for your self-supporting witness cone. Be sure to apply kiln wash to these small surfaces so that they can be reused in many firings.
Cone Packs can also be prepared using a small amount of moist clay for the base to press the cones into or a cone holder. Generally, the cone corresponding to the temperature that the kiln is desired to be fired at (Target Cone) is placed in the center, with a pyrometric cone that is one cone lower (Guide Cone) in front of the Target Cone, along with a pyrometric cone that is one cone higher (Guard Cone) behind the Target Cone.
Self-Supporting Witness Cones
How to Make a Cone Pack
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