If the assay is left in the furnace for too long, the gold will evaporate and lose weight, which is not fair to the Master of the Mint. If it is not left in long enough, some base metal will remain allayed with the ingot of gold, which is not fair to the King. Knowing how long to leave it in there is a black art of the Goldsmiths, and Daniel gets the sense that William is silently polling the other eleven members of his Jury for their opinions. When a consensus seems to have been reached, he picks up the tongs again and withdraws the cupel and sets it on a brick to cool down. The lead jacket has vanished and the cupel has turned charcoal-gray. Remaining in the top of the cupel is the ingot: a tiny round lake of gold. The stars and moons that decorated Mr. Threader’s black firmament have been changed by alchemy into this little sun. They need only wait for its heat to subside before they take the weight of it.