Improving Kiln Uniformity
Temperature distribution in your Kiln
Improving Kiln Uniformity
Understanding Kiln Uniformity
Temperature distribution inside a kiln can be affected by many different factors including:
- the design of the kiln
- the kiln firing temperatures
- how the kiln is loaded
- the rate of heating
- whether the kiln is vented
- if a soak (hold) is used
- the aged and condition of the heating elements inside the kiln
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Efficient Kiln Loading
Loading a kiln is like loading a dishwasher. Organise items to be glazed according to size. This increases efficiency of space and better heat distribution.
- Before placing any items on the kiln shelves, position the kiln props. Typically three props are used on circular shelves; four props are used for square shelves.
- Next begin to load your ceramic pieces on the kiln shelf. Do not over pack the shelf and ensure there is good ventilation around each item. Remember that larger items benefit by being placed in the centre of the shelf - known as the pyramid method (e.g. taller items in the middle, smaller items on the outside). This is so that the heat from the kiln elements can circulate more easily.
- Arrange items evenly in the kiln to allow airflow to pass between everything, be especially careful not to have glazed pieces touching each other or they will stick together. Glazed ware needs to be at least 1/4" apart due to thermal expansion during the firing process. The ceramics should not touch the kiln walls or props either.
- It is a good idea to put shorter pieces at the bottom of the kiln and taller pieces at the top. This is because tall posts (props or shelf risers) tend to fall over easily which may result in damages.
- Ensure each shelf is exposed to at least 1 or 2 elements. This is particularly important for short or flat items like plates.
- When adding new shelves, remember to allow at least ½” above the tallest item to allow for thermal expansion.
- Top tips when firing larger/heavier/thicker items:
- Ensure the pieces are fired slowly.
- Ramp times should be approximately 100°c-150°c per hour up to 600°c. This will slow down the heat process and will reduce the likelihood of items cracking at this stage during the firing process.
- Beware of a special type of crack called Dunting. Dunting occurs from stresses caused during firing and cooling. Some Dunting cracks are caused during cooling and appear as long, clean, body cracks with sharp edges that could be vertical, horizontal, or spiral. Typically, the top of the item will cool much faster than the bottom, because the bottom has the whole temperature of the kiln shelf keeping it warm. Therefore the top of the item will cool faster than the bottom, causing a crack at the base. To prevent these cracks, avoid placing the piece directly on the kiln shelf but raise the item by 1" using a combination of props and stilts. These steps will give good ventilation around the entire piece, help eliminate cracking during the glaze firing and promote even heat distribution during the heat and cool down sections of the kiln firing process.
- Tile setters can be used to fire more than one tile. Plate cranks can be used to fire plates, single point stilts can be used to fire baubles and bead racks can be used for beads or hanging decorations. Remember to make sure glaze does not come into contact with these firing accessories.
- Prior to pressing the start button, check all around the kiln for potential problems. Do not leave flammable materials on or near the kiln.