What do you mean by etching?

An example of silicate material is glass. Remember that silica is represented as SiO₂.So compounds containing silica & silicates are attacked by hydrogen fluoride gas or its aqueous solution. When reacted with HF gas, SiF₄ gas is evolved. This is represented as

SiO₂ + 4HF--->2H₂O + SiF₄.

But in solutions H₂SiF₆ is formed. This is given as

SiO₂ + 6HF----> H₂SiF₆ + 2H₂O.

Etching means the attack of HF on glass.