How Lenses Are Made - Part 1
Mold-Making
Before a lens blank can be created, we have to start with the foundation: a pair of molds, one front and one back. These molds are what we use to form the “puck” that eventually becomes a prescription lens.
Two Approaches to Mold Making
For mass production, companies often use nickel electroplating, creating long-lasting molds that can produce thousands of lenses. But at Chadwick, we specialize in small-batch, precision work. That means we craft molds in-house using glass blanks surfaced right here in our lab - perfect for unique, one-off lenses.
Similar to processing prescription lenses, we start with a solid glass puck. Using precision cutting, we shape curves into the backside of the mold.
- For standard molds, we cut a single spherical curve.
- For the more complex, we cut a curve on top of a curve.
Blocking and Generating
Before cutting, the glass needs to be mounted. We attach a small block to the back of the puck using wax or alloy.
From there, the glass goes into a generator:
- The generator holds the lens securely.
- A diamond bit spins and moves to cut precise curves into the glass.
- After this step, the glass looks frosted due to all the tooling marks.
Shaping the Mold
During the fining process, we use sphere polishers which rotate in place instead of moving back and forth like the polishers used on prescription lenses. Since glass is very hard, we rely on diamond tools and abrasive liquids to achieve an ultra-smooth, optical-quality surface.
Polishing to Optical Clarity
The next step is polishing. Using sphere polishers with abrasive liquids, we smooth the surface until it’s crystal clear. This ensures the final cast lenses don’t require extra finishing and are ready for optical processing right away.
Once polished, we verify that the curves are correct with sag gauges. These instruments measure the depth of the curves, which we then translate into exact optical specifications.
Ready to Cast
When the mold is fully polished, measured, and approved, we remove it from the blocker. It’s then ready to move into our lens casting department, where it becomes part of the process of creating your custom prescription lenses.
