Ceramics and glass are machined by:

The correct option is ultrasonic machining.

Detailed Explanation:

Ultrasonic machining (USM) is a non-traditional, mechanical material removal process. In this process, high-frequency electrical energy is converted into mechanical vibrations using a transducer. These high-frequency, low-amplitude vibrations are transmitted to a tool. An abrasive slurry, typically containing fine abrasive grains like silicon carbide or boron carbide suspended in water, is continuously pumped into the gap between the vibrating tool and the workpiece.

As the tool vibrates, it hammers the abrasive particles against the surface of the workpiece. This action causes micro-chipping or microscopic erosion on the workpiece surface. Because material removal depends on the brittle fracture of the workpiece material under the impact of abrasive grains, ultrasonic machining is exceptionally well-suited for hard, brittle, and non-conductive materials.

Ceramics and glass are classic examples of materials that are extremely hard and brittle. They are also electrically non-conductive, which rules out thermal or electrical chemical processes like Electric Discharge Machining (EDM) or Electrochemical Machining (ECM) since those require a conductive workpiece. Therefore, ultrasonic machining is the highly preferred and standard method for machining intricate shapes, holes, and cavities in glass and ceramics.