Etching is the means to leave a permanent mark on the surface of a material (for the purpose of my website, primarily glass).
As the etching is carried out this leaves a mark that can vary from barely visible through to fully opaque. With careful skill this can be continually varied to create a shading or gray-scale effect.
When applied to an area this is referred to as “frosting” – this is putting an even etched or engrave area onto the parent object to make a flat even area of altered surface texture. In the case of glass this leaves a strong white semi-opaque mark on the glass compared to the clear translucent parent material. It is similar in texture to that of a sharp frost on a winter’s morning.
By careful selection of where the etching is carried out, this can give a clear frosted design on a clear (or whatever colour the parent glass is) background or this can be reversed to leave a darker clear design floating on a frosted background as this picture demonstrates.