An acid stain mixture is made up of inorganic metallic salts in an acidic and water solution. This mixture chemically reacts to your concretes surface which allows stains to etch their way into your concrete. Once the full chemical reaction has taken place an acid stain becomes part of the concrete and will not chip, fade, or peel.
You cannot always predict with certainty a color that acid staining will produce on different surfaces. Each situation is different, meaning, each surface will allow the acid stain to penetrate its pores at different degrees. Acid stains produce beautiful earth colors like blues, greens, browns, tans, etc.