Polishing Optical Glass – Optical Glass (CTE 7.1 x 10^-6 /K, 350 nm – 2.0 um); Polishing to flatness to lambda/4 per 25 mm. No minimum order; DFM review included with every RFQ.
polishing optical glass is a materials problem before it is a machining problem. Optical Glass has certified refractive index and dispersion and a Knoop hardness of 610 kg/mm2, so the polishing recipe – feeds, coolant, tooling – differs from what works on ordinary float glass. The line runs pitch and polyurethane pad polishers with cerium oxide slurry and holds flatness to lambda/4 per 25 mm.
Key parameters
| Material | Optical Glass (N-BK7, H-K9L and filter glass sets) |
|---|---|
| Thermal expansion (CTE) | 7.1 x 10^-6 /K |
| Service temperature | 400 C (Tg 557 C) |
| Transmission range | 350 nm – 2.0 um |
| Density | 2.51 g/cm3 |
| Knoop hardness | 610 kg/mm2 |
| Refractive index | 1.5168 @ 587 nm |
| Stock thickness | 0.30 – 50 mm |
| Maximum blank size | 300 mm diameter |
| Process | Polishing |
| Working tolerance | flatness to lambda/4 per 25 mm |
| Minimum feature | Ra below 1 nm |
| Surface finish | scratch-dig 40/20 to 20/10 |
| Thickness window | 0.2 – 50 mm |
| Edge condition | polished bevels available |
| RFQ inputs | PDF/DXF/STEP drawing, quantity brackets, surface and edge spec |
Design guidance
Three items decide most of the cost and lead time on this work:
- Material note: index-certified blanks must be oriented and serialized through the shop to keep melt traceability.
- Process boundary: steep aspect parts and deep pockets polish unevenly; those faces are specified as fine-ground.
- Over-specification is the quiet budget killer: a 20/10 scratch-dig face costs roughly three times an 80/50 face, so grade each surface individually.
The full rules live in our tolerance design guide and holes and edges design guide.
Manufacturing capability
The core strength of Polishing is optical-grade faces with certified scratch-dig and interferometer-verified flatness. The honest limit: steep aspect parts and deep pockets polish unevenly; those faces are specified as fine-ground. Both belong on the drawing before quoting, not after.
One material, many routes: on Optical Glass we also quote double-side polishing, drilling, dicing, laser cutting, and multi-step drawings are the norm rather than the exception.
Who orders this
Orders for polishing optical glass cluster in optical sensors (sensor windows, filter caps, lens covers); laser systems (windows, beam splitters, debris shields); ccd inspection equipment (CCD cover plates, reference grids, stage glass). Background reading on the underlying material science: RP Photonics: optical glass.
The fastest route to a quote is geometry: use the 3D configurator below, or the site-wide custom glass machining 3D builder for fully custom parts.
Related reading on this site: JGS1 quartz glass, precision glass grinding, holes and edges design guide.
Frequently asked questions
What tolerances are achievable on Optical Glass parts?
Ground features hold +/-0.01 mm and lapped thickness reaches +/-0.003 mm. Index-certified blanks must be oriented and serialized through the shop to keep melt traceability.
What thickness range do you stock for Optical Glass?
Standard stock spans 0.30 – 50 mm, with blanks up to 300 mm diameter. Other formats are sourced per order.
How does Optical Glass behave under heat?
CTE is 7.1 x 10^-6 /K and continuous service reaches 400 C (Tg 557 C), which is what drives its use where certified refractive index and dispersion matters.
What accuracy does polishing hold?
Flatness to lambda/4 per 25 mm with minimum features of Ra below 1 nm. Steep aspect parts and deep pockets polish unevenly; those faces are specified as fine-ground.
Specifications on this page were last reviewed by our engineering team in July 2026.