Molten chocolate can be tested for its temper by placing a small, thin portion on a room-temperature surface, a plate or piece of foil. Properly tempered chocolate solidifies in a few minutes to a clean, silky-surfaced mass; the side in contact with the cool surface is shiny. Chocolate out of temper takes many minutes to harden, and has an irregular powdery or grainy appearance.
From the book On Food and Cooking (2nd edition) by Harold McGee. © 2004 Harold McGee.
By permission of Scribner, a division of Simon & Schuster, Inc.