179. All stone is better for being exposed in the air until it becomes dry before it is set. This gives a chance for the quarry water to evaporate, and in nearly all cases renders the stone harder, and prevents the stone from splitting from the action of the frost.

Many stones, particularly certain varieties of sandstone and limestone, that are quite soft and weak when first quarried acquire considerable hardness and strength after they have been exposed to the air for several months. This hardness is supposed to be caused by the fact that the quarry water contained in the stone holds in solution a certain amount of cementing material, which, as the water evaporates, is deposited between the particles of sand, binding them more firmly together and forming a hard outer crust to the stone, although the inside remains soft, as at first. On this account the stone should be cut soon after it is taken from the quarry, and if any carving is to be done it should be done before the stone becomes dry, otherwise the hard crust will be broken off and the carving will be from the soft interior, and hence its durability much lessened.