Loading A Pottery Kiln
Stacking and loading a kiln for best results
Basic Kiln Loading Tips
Loading a kiln is a bit like loading a dishwasher i.e.(1) you want to load it efficiently to make sure you maximise the space and (2) instead of making sure water can reach every part of your crockery, you need to make sure heat and oxygen can reach all wares.
Loading a kiln for firing is not a simple matter of placing shelves and stacking ware. The more thought and planning that is put into loading, the better the results.
Common Points to remember:
- Make sure the base shelf has not been placed on the actual base of the kiln i.e. make sure it has been placed on props (minimum 1” high) to ensure there is correct air circulation underneath the base kiln shelf.
- Check the items. Has it been dry-footed or will you use a stilt? Is the item fully dry? Are all the products used on the item compatible and do they share the same recommended firing temperatures? Do some pieces have underglazes or glazes that could potentially drip or “spit”?
- Carefully plan where you will place each item - make a note of where you will position the kiln props. Typically three props are used on circular shelves; four props are used for square shelves.
- Remember not to knock the THERMOCOUPLE as you load the kiln. The Thermocouple is classed as a “wear and tear” item and will need replacing if damaged
- Place taller items in the middle of the kiln and shorter items on the outside. This is known as the pyramid method – taller items may block the heat from the kiln elements if placed on the outside of the shelf.
- Consider using half shelves for taller items (a half shelf will utilise space more efficiently and improve air movement).
- Remember to leave enough space around each item to allow for thermal expansion (at least one or two centimetres around each item). More space is required over the top of the item (particularly with short pieces like plates) to allow for heat transfer from elements and airflow etc. Be especially careful not to have glazed pieces touching each other or they will stick together.
- Wares should not touch the kiln walls or props.
- Mix thick and thin walled item together on shelves so that they are not competing for heat.
- Do not overload the kiln otherwise the airflow or heat transfer will be affected. Also, an overcrowded kiln does not provide enough oxygen for the carbon to be eliminated so you may find some pieces could potentially look blackened after firing.
- Consider where each shelf will be placed. Remember to ensure that at least one or two elements can heat each layer of shelving.
- Finally, check that the kiln firing programme is correct before pressing the start button. Also, before leaving the kiln area, check that there is nothing around or on top of the kiln that is a fire hazard.
- 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.
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.
Orton Ceramics have produced a PDF document outlining the requirements for Kiln loading CLICK HERE to view