# What Is Candling?

Unit: The First Bake: Bisque Firing
Topic: Bisque Firing Schedule
URL: https://claybook.studio/learn/what-is-candling/

# The Slow Start That Saves Everything

Candling is the practice of holding the kiln at a very low temperature (typically 80–120°C (175–250°F)) for an extended period at the beginning of a firing. It is a safety measure, and it is one of the most important habits in ceramics.

## Why Candle?

Even pots that appear completely bone dry can retain trace amounts of atmospheric moisture absorbed from a humid studio. Bone-dry clay is also still physically porous, and in a humid environment, it re-absorbs water from the air over time.

When candling:

*   The kiln heats slowly, giving any remaining moisture time to evaporate gently as water vapor rather than steam.
*   The heat moves evenly through thick sections without building up the pressure that causes explosions.
*   It acts as an insurance policy, especially valuable for thick-walled pieces, large forms, and any work that was rushed in drying.

## How Long to Candle?

The standard recommendation:

*   **Thin-walled pieces (mugs, bowls)**: 1–2 hours of candling at 80–100°C.
*   **Medium pieces (vases, larger bowls)**: 2–3 hours.
*   **Thick pieces (sculpture, large vessels)**: 3–6 hours or more.

If you are unsure, err on the side of longer. Candling adds a little time to the total firing but costs almost nothing in electricity and prevents the catastrophic loss of an entire kiln load.

## Candling Decision Guide
Choose duration by highest-risk piece:
* If one thick piece is present, candle for thick-piece timing
* If humidity is high, add extra hold time
* If unsure, extend rather than shorten

Candling time is cheap compared to load failure.

## Go Deeper

Candling is the gentlest phase of a process that eventually leads to [sintering](https://en.wikipedia.org/wiki/Sintering), where clay particles permanently fuse together at higher temperatures. The Wikipedia article on [kilns](https://en.wikipedia.org/wiki/Kiln) explains how different kiln designs manage the slow temperature ramps that make candling effective.

## Check your understanding

### Question 1: What is the main purpose of candling at the start of a bisque firing?

- [ ] A. To pre-heat the kiln furniture
- [x] B. To allow remaining moisture to escape safely before high heat
- [ ] C. To burn off the kiln wash
- [ ] D. To check the kiln is working before the main firing

Tip: Candling allows any remaining moisture to evaporate gently and safely before the kiln reaches temperatures that would turn it to explosive steam.

### Question 2: How long should you candle a thick-walled sculpture or large vessel?

- [ ] A. 30 minutes is always enough
- [x] B. 3–6 hours or more
- [ ] C. 1 hour maximum
- [ ] D. Thick pieces do not need candling

Tip: Large, thick pieces should be candled for 3–6 hours or more to ensure all moisture escapes evenly from their mass.

### Question 3: You normally skip candling, but this load includes several freshly trimmed thick bowls from a humid week. What is the safest change to your firing plan?

- [ ] A. Raise the peak bisque temperature to burn off more moisture
- [x] B. Add a long candling hold before your normal bisque ramp
- [ ] C. Shorten the firing to reduce time in the kiln
- [ ] D. Open the kiln periodically during the climb to vent steam

Tip: Add a long candling phase at low temperature before your usual bisque schedule. That single change dramatically lowers explosion risk for thick, recently trimmed ware.