Within the past ten years a great impetus has been given to the production of special colors in architectural clay products. In 1885 fully four-fifths of the terra cotta produced in the United States was red; now hardly one-fifth is of that color. Buffs and grays of several shades, white and cream-white and the richer and warmer colors of the fire-flashed old gold and mottled are now the prevailing colors.
By the use of chemicals almost any required tone or color may be obtained. As a rule, however, it is safer, and a better quality of material is likely to be obtained, by using only those colors which are natural to the clay. A color which necessitates underburning or overburning of the clay should not be used.
If any particular color, not natural to the material, is desired the architect should consult with the manufacturer in regard to its effect upon the durability and quality of the finished product.
The modern employments for terra cotta, architecturally, are for tiles, panels and medallions; pilasters, columns, capitals and bases; sills, jambs, mullions and lintels; skewbacks or springers, arches and keys; spandrels, pediments and tympanums; mouldings, belt courses, friezes and cornices; coping, chimney tops, cresting, finials and terminals.
Terra cotta is also employed for brackets, consoles, gargoyles, corbels, oriel and tracery windows, and for interior use for altars, baptismal fonts, balusters, newels, pedestals, statues, niches, mantels, fireplace facings, and in fireproof buildings for base mouldings and base panels, and also in plain blocks for ashlar.
Terra cotta is also suitable for all kinds of garden decorations, such as balustrades, ferndelabras, flower baskets and vases and other horticultural appliances.
The principal value of terra cotta lies in its durability. When made of the right material and properly burned it is impervious to wet, or nearly so, and hence is not subject to the disintegrating action of frost, which is a powerful agent in the destruction of stone; neither does it vegetate, as is the case with many stones. The ordinary acid gases contained in the atmosphere of cities have no effect upon it, and the dust which gathers on the mouldings, etc., is washed away by every rainfall. Underburned terra cotta does not possess these qualities in so great a degree, as it is more or less absorbent. Another great advantage possessed by terra cotta is its resistance to heat, which makes it the most desirable material for the trimmings and ornamental work in the walls of fireproof buildings. Although terra cotta has been used in this country for but a comparatively short time, it has thus far proved very satisfactory, and the characteristics above indicated would point to its being, in common with the better qualities of brick, the most durable of all building materials.
In Europe there are numerous examples of architectural terra cotta which have been exposed to the weather for three or four centuries and are still in good condition, while stonework subjected to the same conditions is more or less worn and decayed.