Optical Coating Preparation
What This Process Needs To Solve
The polishing step before coating is not judged by how the surface looks. It is judged by what is underneath it. A lens that passes a visual check can still carry a layer of subsurface damage, and that layer is what fails when the coating goes on and the optic is put into service.
We supply micron powder from W0.5 to W10 for pre-coating polishing, with polycrystalline grades where the surface has to reach spec without a deep damage layer.
Why subsurface damage decides coating adhesion
Every grinding step leaves cracks that run below the visible surface, and polishing has to remove material past the deepest of them. If it does not, the coating is deposited on a surface that is already fractured at a scale the eye cannot see. The result is not a coating that peels immediately — it is scatter, a lower laser damage threshold, and a part that fails in the field instead of at inspection. The defect traces back to the polishing grade that was too coarse to clear the previous step, not to the coater.
Polycrystalline leaves a shallower damage layer
A monocrystalline particle cuts with defined edges and removes material efficiently, but each edge leaves a crack of a depth proportional to the load on it. A polycrystalline particle breaks down during the pass, so the effective load per edge drops as it works and the damage layer stays shallow. That is why pre-coating work uses polycrystalline grades at the finish even though monocrystalline would cut faster.
What we hold on the batch
The controlling property is the top cut, because one oversize grain on a coated surface becomes one scattering centre. We report D90 and the maximum particle per lot, and can supply a tighter window than the standard grade when the coating specification requires it.
Where It Goes Wrong
- Scatter after coating. Subsurface damage not cleared by the last polishing step.
- Coating adhesion fails in service. Same cause, showing up later and more expensively.
- Isolated pits on a polished surface. One oversize particle in the final grade.
- Polishing takes longer than planned. Starting grade too fine to clear the grinding damage.
Recommended Grade By Polishing Stage
Pre-coating work is specified by how much damage has to be removed, not by the final surface figure alone.
| Stage | Recommended grade | Micron size | Why this grade |
|---|---|---|---|
| Clearing grinding damageAfter fine grinding | |||
| First polishing step | HDYP polycrystalline | W5 – W10 | Removes the damaged layer without driving new cracks deeper |
| Intermediate step | HDYP polycrystalline | W2.5 – W5 | Breaks down in use, keeps the damage layer shallow |
| Final polish before coatingSurface has to be clean and undamaged | |||
| Final polish | HDYP or HDY, tight top cut | W1 – W2.5 | A shallow damage layer is what the coating is deposited on |
| Super-fine finish | HDYM fine micron | W0.5 – W1 | Reaches the surface figure without a deep scratch |
| Slurry supplyPad polishing | |||
| Slurry formulation | HDYP, carrier matched | W0.5 – W5 | Carrier has to keep the powder suspended across a large optic |
Factory Direct Since 1990
Zhecheng Hongxiang Superhard Material Co., Ltd. is an integrated manufacturer and exporter of synthetic diamond powders since 1990, located in the Diamond Capital of China.
- Own manufacturing base in Zhengzhou, Henan — powder, coating and grading on one site.
- In-house particle size and SEM inspection on every batch before packing.
- Export packing with neutral or custom label, plus sample quantities for process trials.
What To Include
Describe your workpiece, process and target result. We will match the diamond grade from the existing product range.