Candling in a kiln is a crucial step in the pottery firing process, specifically designed to safely remove residual moisture from greenware (unfired clay). When using a manual kiln, this process requires careful attention and manual adjustments to achieve the desired conditions described in the reference.
What is Candling?
Based on the provided reference, candling a kiln involves heating pottery for several hours below 212°F. This temperature is significant because it's just below the boiling point of water. Pottery is typically candled at around 185-200°F. The purpose is to cause any remaining moisture in the clay to evaporate slowly, which is essential for preventing pottery from bloating and exploding later in the firing process when water turns rapidly into steam.
Candling Process in a Manual Kiln
Unlike automatic kilns with programmed firing schedules, candling in a manual kiln requires the operator to control the heat and duration manually. Here's how you generally approach it:
- Load the Kiln: Place your bone-dry greenware carefully into the kiln. Ensure pieces are not touching each other or the kiln elements.
- Ensure Ventilation: Adequate ventilation is critical during candling to allow the released moisture to escape. In a manual kiln, this is often achieved by:
- Propping the kiln lid open slightly (e.g., with a small ceramic or brick prop).
- Opening any built-in vent holes or bungs.
- Apply Low Heat: Turn on the kiln to a very low setting. Manual kilns often have multiple element switches or an infinite switch/controller for power levels. Start with minimal power – perhaps only one element on a low setting, or the infinite switch turned just slightly past the "off" position. The goal is a very gradual increase in temperature.
- Monitor Temperature: Use a pyrometer or kiln thermometer to monitor the internal temperature of the kiln. Since it's a manual process, you'll need to check the temperature periodically.
- Maintain the Target Range: Adjust the power settings as needed to keep the temperature within the 185-200°F range mentioned in the reference. This requires vigilance and manual adjustments over the duration of the candling period. If the temperature rises too quickly, reduce the power or momentarily turn off an element.
- Hold for Several Hours: Maintain the temperature within the target range for several hours, as indicated by the reference. The exact duration can vary depending on the size and thickness of the pottery, but a minimum of 4-8 hours is common for thorough drying.
- Transition to the Main Firing: After the candling period is complete and you are confident all residual moisture has evaporated, you can gradually increase the temperature according to your full firing schedule for the specific clay body and glaze you are using.
Practical Tips for Manual Candling:
- Start Low: It's always better to start with too little heat and gradually increase than to start too high and risk thermal shock or rapid steaming.
- Consistency is Key: Try to maintain a consistent temperature within the target range for the entire candling period.
- Listen to Your Kiln: Pay attention to any sounds. Hissing sounds can indicate water turning to steam too quickly.
- Document: Keep notes on settings and temperatures to refine your process for future firings.
By manually controlling the temperature and ensuring proper ventilation at the specified low temperature for several hours, you effectively candle your pottery, following the principles outlined in the reference to ensure a safe and successful firing.
