Remus' directions led him to one of the old classrooms on the third floor, and when Harry arrived ten minutes before curfew he found his lycanthruncle clearing away space in the middle of the room.
"Do we need the space?" he asked.
"Well, I don't know," Remus admitted, as Harry joined him in pushing away benches and long-unused cauldron burners. "But it's always better to have space to move around when you're learning a new spell – and, to be honest, I don't trust those cauldrons."
Once the last of the benches was pushed aside, Remus went to get a book out of his bag. As he did, Harry sniffed the nearest cauldron.
It didn't seem to have any spell residue in it, and a quick light spell on his wand revealed nothing visible in it either. Harry decided to scrape the inside to see if there was any residue left, and while that didn't result in him finding any dried up potion bits he did dig a hole clean through the bottom of the cauldron.
"What's that, Harry?" Remus asked, and Harry looked up a bit guiltily.
"I think I broke the cauldron," he admitted. "Sorry."
Remus used a levitation spell to lift the cauldron, and inspected the hole in it.
"Well, I can see why they didn't bother retrieving them," he said, after a moment. "That's really very thin indeed. I wouldn't be surprised if that cauldron split if it got kicked at the wrong time."
Harry winced, imagining that, then took a bite out of the cauldron as a snack.
"It does taste like good quality pewter, though," he said, swallowing.
Remus gave him a strange look, then shook his head.