Staining imparts a luxurious richness that can’t be achieved by any other coloring medium. Rather than produce a solid, opaque effect like paint, stains permeate the concrete to infuse it with luminous, translucent tones that vary depending on the surface they are applied to and the application techniques used. The results can mimic everything from polished marble to tanned leather to natural stone or even stained wood. Acid stain is a mixture of water, hydrochloric acid and acid-soluble metallic salts. They work by penetrating the surface and reacting chemically with the hydrated lime (calcium hydroxide) in the concrete. The acid in the stain lightly etches the surface, allowing the metallic salts to penetrate more easily. Once the stain reacts, it becomes a permanent part of the concrete and won’t fade, chip off or peel away.