Cuelin laughed, and pulled off his leather gauntlets. “Certain sure. You just wait; as soon as word gets out that we’re replacing a salle mirror up there on the hill, there’ll be a stream of highborn servants at the door. ‘If you’d happen to have a spare window glass, so-by-so, Master Cuelin… if you’re like to have a mirror for milady’s dressing table…’ They know we have to work our way up to a pane that big, and they know they’ll get a bargain they wouldn’t get if they’d commissioned those glass panes and mirrors special. Then it’ll be the polishing, and then the silvering, and that’ll be a bit tricky as well. Master Alberich, I want to show you something that’ll catch your interest, aye, and you, too, Elkin—I had the Collegium servants bring me down the old glass, and when I got it, this is what I found.”

He held up a shard of silvered glass. “This’ll be from the top of your mirror—” and a second, “—and this’ll be from the bottom. Now, what d’ye think of that?”

The top shard was clearly thinner than the bottom. Alberich scratched his head. “Glass not so good as you can make it?” he hazarded.

Cuelin laughed. “Oh, flattery! No, no, it was fine glass, and we’ll be hard put to match it. But I’ll reckon that mirror was over two hundred years old if it was a day, Master Alberich. Maybe more. And when it was made, top to bottom was the same thickness.”

He wanted Alberich to look puzzled; with some amusement, Alberich obliged him. “Then, how?” he asked.

“Glass never quite sets, Master Alberich,” Cuelin told him. “It’s like slow water, my old Master told me. Believe it or not, it keeps flowing—oh, slow, too slow to notice, but over a century or two, or three, you look, you’ll see that any glass has got thicker at the bottom than it is at the top. Mind, most of it doesn’t stay unbroken long enough to find that out, ’specially with lads like your two troublemakers about, but there you have it. You can tell the age of a piece by how thick it’s got on the bottom compared to the top.”

Alberich examined the two shards, then passed them on to Elkin, and blinked at that, and tried to get his mind wrapped around the idea of something that flowed that slowly. “I am—astonished,” he admitted after a moment. “Astonished.”