Lost a piece in the bisque firing last night and I think I know why

Been there, same killer is an unvented cavity. My disaster was a hollow owl for the porch steps, about knee high, and I sealed every gap because I wanted a smooth silhouette. One little hole got covered over during a later handle and I never noticed. Found pieces of owl in places I still can't explain, including a chunk that must have bounced off the kiln lid and landed six feet away on the floor. Since then I drill a hole the width of a pencil through the thickest part of the base before the piece gets too firm, and I do it from the bottom so it's invisible. I also stopped stuffing anything into a fully enclosed cavity. Paper wads that can't burn through to open air just smolder and build pressure, and even with a vent they can leave the inside a mess of carbon stains if the gases have to fight thier way out through a narrow neck. One more thing that saved me on a later piece: if a hole is only partly blocked, say by dried slip or a bit of clay that fell in and plugged it from inside, the explosion looks exactly like a total mystery. I now wiggle a skewer through every vent right before loading to be sure it actually goes all the way through. The shard I kept from the owl sits on my shelf by the wheel and works better than any rule I ever forgot.

Funny how the chimney ended up being the weak point for you, because mine saved a piece once purely by accident. I made a lighthouse for the flower bed last summer, maybe fourteen inches tall, hollow all the way through, and I honestly forgot to plug the top of the tower. Fired it in my little Skutt at cone 6 expecting trouble and it came out fine. I think the open top let everything breathe the whole way up, no pressure buildup at all. Since then I lean the other way from most folks here. Instead of hiding a tiny vent somewhere, I make the opening a feature. My birdhouses get a real entrance hole, my fairy houses get doors and little windows, and anything else gets the top left open or a slot worked into the design. Guests never know it started as a structural necessity. Also, on the paper thing, I quit stuffing anything inside hollow forms years back. I used to use foam and newspaper to prop walls during construction, but now I just build with good even wall thickness, quarter inch or so, and support with my hands while I go. Nothing inside means nothing to burn off or outgas, and drying seems faster too since air can actually move through the piece. Keeping a big shard on the shelf as a reminder is a nice touch though. Mine sits above my work table.

That slow warm-up on top of the kiln only gets you so far, I learned the hard way back in the 80s. Now I candle everything, hold the kiln around the lowest setting for a good long while before letting it climb. Cheap insurance even when the venting is right. My teacher in night class used to say you can't over-dry, only under-fire, and he was right about most things. Sounds like your chimney would've worked fine as a stack if you'd left it open and hidden the hole in the base, exactly like you're planning. The next one will thank you.

The bowl of sorted shards is such a familiar sight, I've got one sitting in my garage from a sealed birdhouse that let go a couple years back. Ended up pressing the biggest chunks into a stepping stone with wet concrete, and honestly it looks better than the original did. Garden stuff is forgiving like that. Are you rebuilding the cottage same design or changing it up? If you're short on patience, a solid packed core with just a shallow hollow for the roof line fires fine too, way less drama.

I'm new to this and I keep reading these threads like horror stories. The bit about the paper stuck inside is what gets me, I whould have done the exact same thing and never thought twice about it. My question is, can you reuse the clay from the bowl of broken bits, or is fired clay basically dead once it's been cooked? I dropped a little pinch pot last month and I've just been staring at the pieces wondering if they can go back in the slop bucket.