What does it mean for a lens to be 'blocked' and what material is used?

• A. The block sharpens the lens edge.
• B. The block holds the lens in place through the entire surfacing process. The material is an alloy or wax.
• C. The block polishes the lens surface.
• D. The block applies a decorative finish.

Answer: (B)

Blocking means mounting the lens blank to a small block so the grinding/polishing machine can hold and rotate it securely during all the surfacing steps. The block provides a stable grip and correct alignment, so material can be removed evenly around the eye.

The block stays attached to the lens through the entire surfacing process, ensuring the axis, thickness, and edge shape stay consistent as the lens is ground and finished. After finishing, the block is removed, and the lens is separated from the blocking material.

Blocking materials are chosen for practicality: soft wax is commonly used for temporary blocking because it’s easy to apply and can be melted away later; metal alloy blocks are used when a more durable, reusable block is preferred.