165. The selection of a stone for structural purposes is a matter of the greatest importance, especially when it is to be used in the construction of large and expensive buildings. The cities of Northern Europe are full of failures in the stones of important structures, and even in the cities of the Northern portion of the United States the examples of stone buildings which are falling into decay are only too numerous.
"The most costly building erected in modern times - the Parliament House in London - was built of a stone taken on the recommendation of a committee representing the best scientific and technical skill of Great Britain. The stone selected was submitted to various tests, but the corroding influences of a London atmosphere were overlooked. The great structure was built (of magnesian limestone), and now it seems questionable whether it can be made to endure as long as a timber building would stand, so great is the effect of the gases of the atmosphere upon the stone." *
* Baker in " Masonry Construction," p. 4.
In selecting a building stone the climate, together with the location, with especial reference to the proximity to large cities and manufacturing establishments, should be first considered. There is many a porous sand or limestone which could endure an exposure of hundreds of years in a climate like that of Florida, New Mexico, Colorado or Arizona, which would be sadly disintegrated at the end of a single season in one of the Northern States. The climate of our Northern and Eastern States, with an annual precipitation of some 39 or 40 inches and a variation in temperature sometimes reaching 1200, is very trying on stonework, and unless a stone is suited to the conditions in which it is placed, there are few materials more liable to decay and utter failure.
The great governing point with an architect in selecting a building stone is generally the color. This again is limited to a choice between those stones which come within the limit of cost, and should be finally overruled by the question of durability. The architect is too apt to think that if a building cannot be pleasing both in form and color it had better not be built at all, but he should keep in mind not only how the building will look when just completed, but how it will appear at the end of a few years, and, again, at the end of half a century. It is better that the colors be a little harsh and inharmonious at first, if durability is gained thereby, than to use the most pleasing color only to see it entirely changed at the end of a year, and crumbling in pieces at the end of a decade.
A durable stone of any color generally tones down and becomes more pleasing at the end of a few years, while one that is not durable and permanent in color very soon becomes an eyesore.
In the country and small towns where there is no manufacturing, and where little bituminous coal is used, light-colored stones may be used with the prospect of their color remaining unchanged; but in large cities and in manufacturing towns, particularly those where bituminous coal is the principal fuel, light stones should be avoided, and for such localities a red or brown siliceous sandstone is the most enduring and permanent, and next to this comes granite.
In a city like Chicago, the darker the stone used the more permanent will be its color (that is, in the central portion of the city), as both brick and stone assume a dirty, dark bronze color in a few years, and in such localities delicate colors and fine carving are out of place.
In climates like that of Colorado, Arizona and New Mexico, where there is a very bright sun and almost no rain, the light stones, and particularly marbles, are most effective, as the shadows on such stones are very marked, and all kinds of ornament are made much more prominent than on red or dark stones, and any compact stone will last for centuries above the ground.
As a rule, all else being equal, the stone which holds its native color best will be most beautiful in a building, and of the stones which change color, that will be most desirable which changes least and evenly.