Actually cooling it in the forge is a great way to ruin the temper. That rapid cooldown in open air is what sets the structure, man. A crack down the middle points to a flaw in the weld, not the quench. If the bond was solid, air cooling wouldn't split it. You gotta blame the prep work, not the final step.

Kids see the pure job.

That's a wild thing to learn after ten years lol. Good on your kid for paying attention in class. I'd be so mad at myself for missing out on good coffee for that long. The hot water tank thing makes total sense when you think about it.