Animal Sculptures by Karen Wilde NZ

Opening the kiln to find a ceramic disaster is a moment I’ll never forget. Two of my mega slug sculptures—big, bold, fully enclosed forms—exploded during firing, taking out most of the kiln load, including a batch of small mini mushroom sculptures. Galleries expecting those pieces will now have to wait longer for the next batch, which is a real setback. Here’s what went wrong and the hard lesson I learned.

I’d crafted three mega slugs, each a hefty, sealed form full of character. I dried them for a few weeks in the studio’s open air, my usual process that’s always worked before. I didn’t do a soak during firing, as I’ve never had issues with pieces not being dry enough. But I made a critical mistake: I forgot to add a vent hole to the base of those slugs. Huge oversight.

The result? Two of the three slugs blew apart in the kiln, scattering shards everywhere. One slug survived, likely bone-dry by sheer luck, but the damage was done. The explosion trashed my mini mushrooms and most of the other pieces, leaving galleries empty-handed for now.

What caused the chaos? It’s all about that missing vent hole and hidden moisture. Let’s debunk a myth: “trapped air” doesn’t cause kiln explosions. Air bubbles don’t expand enough to break clay. The real issue is water trapped in enclosed forms like my slugs. Without a vent hole, two problems arise:

1. Slower Drying: A vent hole lets air circulate through a hollow form, drying it evenly inside and out. Without it, moisture deep in the clay lingers, even after a few weeks, because it can’t escape through thick, sealed walls.
2. Steam Pressure: During firing, any residual water turns to steam at 212°F (100°C). In a sealed form with no vent hole, that steam builds pressure until—boom—the clay shatters. That’s what obliterated my two slugs and wrecked the kiln load.

The surviving slug must have been completely dry, maybe due to thinner walls or a drier studio corner. But luck isn’t a plan. Fully enclosed forms need to be 110 percent dry before firing, no exceptions. Skipping a soak made the risk even higher.

The lesson? Always add a vent hole to enclosed forms. A quick poke with at the leather-hard stage ensures even drying and gives steam an escape route. I’m now obsessive about vent holes and checking dryness—holding pieces to my cheek (cool means wet) or doing a pre-soak at 80 degrees Celsius for a couple of hours. This explosion delayed my gallery deliveries, but it’s sharpened my process.

Here’s to vent holes, bone-dry clay, and kilns that don’t turn into war zones. The next batch of mega slugs and mini mushrooms is in progress, will be vented and extra dry!

Stay sharp in the studio,
Karen Wilde