N o matter how effectively a rock formation has been produced, the coloration process can make or break it. A successful project contains a powerful sense of aging along with realistic staining, shadow and highlights.
Artists must begin with the appropriate combinations of products, including a variety of stains and paints to create different effects on the rock. Unless they’re significantly diluted, acrylic-based paints leave a thicker, more opaque impression, while acid stains produce a nearly transparent wash. Color-enhancing sealers adjust the hue while helping protect the surface.
When applying the paints, stains and sealers, installers should ensure that the layers don’t cake, otherwise there is a risk that the coloring materials will peel.
Acid stains tend to react to the mineral content of the water into which they’re mixed, so some professionals control the result by using distilled water. Rockscapers should keep plenty on hand for those occasions when it is necessary to dilute the paints and stains to make colors more transparent.
GFRC installers may need to begin with some type of primer, generally an opaque overcoat, to provide a uniform surface over the varying finish of the panels and handwork in between. A wash is not a recommended first layer for this type of construction because it would show the differences between the castings and mortar.
Some hand sculptors start with a base of integrally colored concrete to gain that consistency. This adds considerable expense and the concrete still will need to be painted to appear realistic.
Whether the stone is GFRC or hand- sculpted, select a combination of hues when applying each coat. Some installers start with approximately three colors of similar tones. Others will include reds and greens in the first coat to ensure that certain areas stand out more effectively. They eventually will be painted over, leaving behind just a hint of the more striking shades.
At some point, builders generally apply a layer of dots to create depth, to replicate the thousands or millions of tiny dots one would see if they closely studied a natural boulder.
Designers reproduce the effect by adjusting the sprayer for a coarser mist. The dots are blended in by adding another layer of transparent color over them. An additional technique for obscuring the dots was developed by GFRC producer Rock & Water Creations. This involves applying a diluted white overcoat — thinner than a whitewash — over the primer and dots. More colored coats follow to give it the overall brown or gray effect that we see most easily.
Next comes the sealing process. This is completed by highlighting noticeable features and areas, such as deep cracks and sharp points, with a color-enhancing sealer and covering the remainder with a clear product.
When coloring the stone, artists also should accent certain sections to create the illusion of light, shadows or naturally occurring stains.
Creating shadows in the crevices is crucial because it reinforces the sense that the sun doesn’t get inside the cracks and lighten them. A diluted black or dark brown paint or stain can enhance the appearance of depth.
On the other side of the spectrum are highlights. Lighter colors should go on larger, smoother swaths of stone, as well as peaks or the tips of high-relief areas, to indicate bleaching by the sun.
With the shadowing and highlights complete, rock artists can add finer detail, simulating mineral staining with tones that are lighter or darker than the main color. These stains often begin inside of cracks.
In addition, rusty mineral deposits can accumulate on the flakes seen on sedimentary stone. The dry brush method can be employed to reproduce this effect. Here, the installer covers a brush with thicker acrylic paint, shakes it until almost dry, then lightly brushes the color across the top of the flaking area.
In more humid regions and for grottos, installers can simulate moss and lichens by applying greens around the rim of the water and other moist areas.
Use lighter, brighter coloring in areas where a rock would have split off. This indicates that little or no weathering has yet occurred, so the surface is closer to its original hue.