Etching is a method for decorating pottery where  sharp tools are used to furrow grooves into the surface of pottery while it is in a leather-hard state.  Only transparent glazes can be used with shallow etchings which would otherwise become hidden.  Tinted glazes can be used to darken the decorative grooves naturally because ambient light must pass through a thicker layer of glaze before it is reflected.  Optionally,  grooves can be emphasized with color before glazing by filling them with engobe*.

*engobe – a ‘slip’,  or clay that has been liquified with water, and colored with raw mineral oxides suitable for the high heat of firing.