From Raw Crystal to Luxury Timepiece: How Sapphire Watch Cases Are Made From 0 to 1
A behind-the-scenes look at the complete sapphire watch case production process—from crystal growth to final polishing.
Step 1: Growing the Synthetic Sapphire Crystal
The journey of every sapphire watch case begins in the lab—not in the mine. Synthetic sapphire is created through the Kyropoulos or Verneuil method using pure aluminum oxide (Al₂O₃), grown into large boules under extreme heat and pressure.
Purity: >99.99% Al₂O₃
Growth duration: 2–4 weeks
Boules size: Up to 45 kg
Color doping: Add elements like Cr, Ti, Fe, Ni to create blue, pink, yellow, green, and other hues
Once cooled and stress-relieved, the sapphire boule is ready for slicing.
Step 2: Rough Cutting & Pre-Shaping
The solid sapphire boules are sliced into blocks using:
Diamond wire saws
Laser cutting for fine pre-forms
Waterjet or ultrasonic machining for rough outer contours
At this stage, tolerances are wide, but internal stress management is critical to prevent future cracking.
Step 3: CNC Machining the Watch Case Geometry
Using 5-axis CNC machining centers, the sapphire block is milled into its final form. This stage is the heart of the process.
Machine tools: PCD tools, diamond-coated end mills
Tolerance: ±0.005 mm
Cutting speed: Ultra-low to prevent chipping
Coolant: Water or oil mist to manage heat
Typical parts: Case middle, bezel, caseback, crown guards
Special attention is given to hole drilling for screws, gaskets, or mechanical parts, often requiring laser-assisted drilling.
Step 4: Color Enhancement (Optional)
For colored sapphire watch cases, coloration is achieved during crystal growth—but further enhancement may include:
Thermal treatment to intensify tone
UV filtering coating to preserve color
Chemical etching for anti-reflection
Uniformity of color across batches is critical for brand consistency.
Step 5: Optical Polishing & Finishing
Polishing sapphire is both an art and science. The aim is to achieve a mirror-like finish with zero distortion and minimal haze.
Diamond slurry polishing
Step polishing to avoid edge rounding
Ra < 0.02 µm finish
Manual inspection under polarized light
A single case can take up to 40 hours of polishing time depending on geometry and clarity requirements.
Step 6: Assembly Preparation
Once machined and polished, the sapphire parts are ready for:
Gasket seating surface checks
Waterproof pressure testing
Ultrasonic cleaning
Coating (e.g., anti-reflective, anti-fingerprint)
At this point, the sapphire case is ready to meet metal components or mechanical movements.
Challenges & What Sets Minnexon Apart
Producing sapphire watch cases is notoriously difficult, with failure rates of up to 30% in unoptimized environments. Key challenges include:
Cracking during machining or post-polish
Color mismatch
Micron-level tolerance misalignment
At Minnexon, we overcome these with:
In-house crystal growth and coloring expertise
Precision 5-axis sapphire CNC systems
Advanced polishing automation & inspection
Experience serving Swiss and French luxury brands