Coloring By Immersion

Still another way of varying the color of concrete surfaces is by immersing the finished object in some solution that will dye or stain it.

"The importance of thoroughly mixing colored pigment with the cement before adding the aggregates should be appreciated by anyone attempting to make concrete in colors. If the object being made must possess a certain maximum of strength, it should not be placed in the coloring bath until the concrete has thoroughly hardened, as filling the pores with the coloring matter in solution stops the chemical action or changes taking place in the cement leading to hardening of the concrete.

"Coloring by absorption is effective on surfaces of concrete after it comes out of the mold or after being treated with acid or tools. Surfaces that have been colored by absorbing mineral or metallic colors are less absorbent and the action of the weather on the metallic colors is the same as on real metals, increasing the beauty of coloring by the usual oxidization noticed on bronze and copper. Surfaces of concrete treated by such methods become so hard and dense that they will take a uniformly dull or high gloss polish. Flower pots, vases, flower boxes and similar wares finished by this method are very attractive, the artistic possibilities of such treatment being limited only by the colored sands and taste employed by the worker. Aniline colors and the sulphates of copper and iron are considered best adapted to the making of solutions in which to color concrete by this capillary method."*

Another example of tooled surface finish.

In aiming at color effects secured in part by mixing colors with the cement used to make a batch of concrete, it is very essential-if permanent tints are to be secured-that only reliable pigments be used. The cement, sand and coloring matter are mixed together dry, and it is advisable to experiment a little to find how much color is needed to give the desired shade. When water is added to the mixture, the mortar will appear considerably darker than the final surface will be when thoroughly hardened. By mixing 5 pounds of coloring matter with a sack of cement, the following colors are obtained:

*From "Concrete," published in Detroit.

Raw iron oxide will give a bright red;

Roasted iron oxide will give brown ;

Ultramarine will give bright blue;

Yellow ochre will give buff to yellow;

Carbon black or lampblack will give a gray to dark slate;

A mixture of equal parts of carbon black and red iron ore gives dull reds. In all cases the addition of mineral colors causes some loss of strength but this is not of great importance on ornamental work. In general, only mineral colors are to be recommended as regards permanence of effect produced. Blues and greens are not reliable and will fade in course of time.