To engrave glass, use a diamond-tipped rotary engraving tool, a sandblasting tool or a chemical etching process. The first two require special tools and a significant amount of freehand art skill, while the third is easier but more limited in the type of engraving it can accomplish.
Rotary tools are electronic devices similar to drills. They have multiple speed settings and multiple tips for different applications. Typically, they have ball tips for fine details, cones for arcs and shading, cylinders for circles, stippling and curved surfaces, cone and cylinder combinations for writing or drawing, and Christmas tree tools for shading flat areas and arcs. They will also have discs for dots and circles and teardrops for deep carving, feathering and tapering. Users need to practice with the tools, take all safety precautions and keep the glass cool with a spray bottle of water so it does not shatter.
The sandblasting method requires the glass to be covered with a film mask to protect the areas not to be engraved and expose the rest. Then, the object is placed in a sandblasting cabinet and permanently engraved.
The chemical method also requires a mask, but it can be cut from vinyl shelf paper. Once the pattern is adhered to the glass it is painted with an etching cream and then sponged off with water after the appropriate time. Wear rubber gloves and make sure the room is well-ventilated. The etching cream is caustic and toxic.