Steel that is kept red hot for a long period also is materially weakened. On the other hand, its temperature must not be lowered so fast that the metal chills and hardens. The work should be left in the annealing box until nearly, or quite, cold.
Another method of annealing steel consists in packing the pieces in some material in an iron box, placing the box in a furnace, and heating it until the contents are red hot throughout. The pieces may then be removed from the furnace and allowed to cool while in the box. When removed from the furnace the box should be placed where no current of air or any moisture will strike it.