In the precision optics and glass processing industry, a common question we hear from engineers is: “Will increasing the concentration of diamond powder in my slurry automatically lead to a better polish?”
The short answer is yes, you can use high concentration diamond powder, but “more” is not always “better.”
At SinoDiam, with decades of experience supplying abrasives for optical manufacturing, we know that achieving the perfect optical finish is a balancing act. It requires understanding the relationship between particle density, glass hardness, and pressure.
The Role of Concentration in Glass Polishing
Concentration refers to the amount of diamond carat weight per unit of volume in your carrier fluid (slurry) or compound.
When polishing hard materials like sapphire or quartz glass, a high concentration (typically defined as above average particle density) is often beneficial for the roughing (lapping) stage. More cutting edges in contact with the workpiece mean a higher Material Removal Rate (MRR).
However, for the final polishing stage of softer optical glass (like BK7), an excessively high concentration can sometimes be counterproductive.
The Risks of Over-Concentration
While it is tempting to maximize concentration to speed up production, here is why expert caution is needed:
- Diminishing Returns: There is a “saturation point” in every polishing process. Once the polishing pad is fully engaged with diamond particles, adding more powder won’t increase speed—it will only waste expensive material.
- Scratching Risks (Agglomeration): High concentrations increase the risk of particles clumping together (agglomeration). These clumps act like larger particles, causing deep, rogue scratches on an otherwise perfect lens.
- Rolling Effect: If the concentration is too high, particles may roll over each other rather than embedding in the pad and cutting the glass, reducing the polishing efficiency.
The Physics of the Polish: Why “Pressure Makes Diamonds” Matters
To understand how to use high concentration powder effectively, we must look at the mechanics.
You have likely heard the famous idiom that pressure makes diamonds. While this usually refers to the geological formation of gemstones, it is surprisingly relevant to your workshop. In glass polishing, the diamond powder alone does not do the work; it is the combination of the down-pressure from your machine and the diamond particles that creates the finish.
If you use a high concentration of diamond powder, you must ensure your machine applies the correct pressure.
- Too little pressure: The abundant diamond particles will just hydroplane over the glass surface without cutting.
- Correct pressure: Forces the high density of particles to engage with the glass, fully utilizing the high concentration to maximize removal rates.
Best Practices: When to Use High Concentration
Based on our testing and customer feedback at SinoDiam, here is our recommendation for glass applications:
- Rough Lapping (Grinding): YES. Use high concentration (e.g., micron sizes 10-20μm or larger). The goal here is rapid stock removal and flatness. High concentration excels here.
- Intermediate Polishing: MODERATE. Transition to a standard concentration.
- Final Super-Polishing: LOW to MEDIUM. For sub-micron surface roughness (Ra), a lower concentration with a very fine particle size (0-0.5μm or 0-1μm) usually yields the clearest, haze-free finish on glass.
Conclusion
Using high concentration diamond powder for glass is a powerful technique when used at the right stage of the process. It offers aggressive removal rates for hard glasses and roughing stages but requires careful management to avoid waste and scratches.
Need help formulating the right slurry for your optical glass project? Contact the experts at SinoDiam. We can help you determine the optimal concentration and micron size to balance cost and quality.
