Watch how to etch glass with vinyl stencils and sand

Plotters with precision cutters certainly make glass etching easier that making stencils by hand, but it's still very labor intensive.

Fun fact: they call pulling the unwanted bits out of the stencil "weeding."

Bonus video: how to repair stained glass:

How To: Etch Glass - Sand Blast Carving Technique - Royal Engineers Cap Badge (YouTube / The Stained Leaded Glass Company)