It has chemically reacted with the top layers of the concrete itself, so it isn't going to wear off or change much over time. The only exception is with blue and green hues of stain. While beautiful ...

As soon as that acid stain hits the concrete, it's chemically reacting ... What if your client wants a black color? A. You're basically doing everything with the acid stain up until the point ...

Pigments impart black, white or a color to other materials ... Penetrating stains – When applying penetrating stains, the concrete surface must be void of any paint, stain, coatings or sealers ...