Sentence Examples with the word etch

In fact the uniformity of brass and bell-metal is only superficial; if we adopt the methods described in the article Metallography, and if, after polishing a plane face on a bit of gun-metal, we etch away the surface layer and examine the new surface with a lens or a microscope, we find a complex pattern of at least two materials.

The acid used to etch the surface has darkened the parts richest in copper, while those richest in tin remained white.