What is an etch? How is an etch repaired?
An acidic substance (in this case lemon juice) is spilled onto the marble/limestone.
The lemon juice sits on the marble, reacting with the surface, eating away at the stone.
The affected area is left rough and pitted: the lemon juice has broken down the stone.
The first step to repairing the etch requires grinding into the surface past (deeper than) the damaged area.
The area is then gradually feathered out to match the surrounding stone using a series of consecutively finer/smoother diamond grinding disks.
The area is then polished/honed to match the surrounding undamaged material. Sealer to finish.