Hydrofluoric acid is commonly used to etch glass. It is an exceedingly dangerous acid and should only be used by experienced professionals. Because it is so strong, it is usually only used in manufacturing environments.
Hydrofluoric acid works by eating the surface of the glass exposed to it. In order to prevent all of the glass from being etched, a stencil is used. An advantage of using hydrofluoric acid compared to other methods of glass etching is that the acid deeply etches the glass. Proper equipment must be worn when working with this acid, as it can cause serious burns.