Same Grit, Fewer Scratches. Diamond Sanding in Ceramics
Why Diamond Abrasives Leave Fewer Scratches at the Same Grit
When talking about sanding or polishing in ceramics, it’s very common to hear phrases like:
“This sandpaper is grit 120,”
“I use grit 60 for rough sanding and 120 for refining,” etc.
And up to that point, everything is correct.
However, there is an idea that often surprises people when they start working with diamond abrasives:
At the same grit, diamond usually leaves fewer scratches than other abrasives, such as silicon carbide or traditional sandpaper.
The explanation lies in something that is rarely discussed: what abrasive grains actually look like—and how they behave—when we observe them under a microscope.
Grit Is Not Everything
The grit number (60, 120, 220…) gives us an idea of the average size of the abrasive grain, but it does not describe its shape, nor how that grain behaves when working on a ceramic surface.
Two abrasives can have the same grit and still:
- Leave deeper or shallower scratches
- Produce a cleaner or a rougher surface finish
The key lies in grain morphology and its stability during use.
What Happens When We Look at Clay Abrasives Under the Microscope
In technical studies, optical microscopes and, above all, scanning electron microscopes (SEM) are used to observe the real structure of abrasive grains.
This is where very clear differences begin to appear.
Diamond Grain: Clean and Stable Cutting
When an abrasive diamond grain is observed under the microscope, it shows:
- Well-defined facets
- Clearly defined cutting edges
- A shape that remains stable over time, because diamond is extremely hard
This means that, when working on ceramics:
- The grain cuts the material rather than tearing it away in an uncontrolled way
- Scratch depth tends to be more uniform
- The appearance of uncontrolled micro-chipping on the surface is reduced
In practice, this often results in a very familiar feeling for those using diamond for the first time: “It feels finer than the grit rating suggests.”
It isn’t.
It is the same grit—but the cutting action is different (and more stable over time).
Silicon Carbide and Traditional Sandpaper
Silicon carbide (SiC) is also a hard abrasive widely used in ceramics, especially in sandpaper.
When its grains are observed under the microscope, we can see that they:
- Have a more irregular shape
- Tend to fracture during use (they are softer than diamond)
- When they break, they create new cutting edges—but also unpredictable fragments
For this reason, after sanding with paper (SiC or similar), it is often necessary to move through more grit steps to remove visible marks.
In other words, a more irregular or more fragile grain creates different scratch patterns on the surface during sanding or polishing.
An Important Note: Not All Diamond Abrasives Are the Same
This point is crucial and worth stating clearly. Although it is not the main focus of this article, it is very important.
Even when two tools indicate the same grit, the final result is strongly influenced by:
- Diamond quality
- The sintering process
- Grain distribution
- The backing or support to which the diamond is bonded
For this reason, in diamond tools, the grit number is only a reference—not an absolute guarantee of performance.
This is also why we do not specify a grit number on our diamond discs for the pottery wheel. Besides the fact that people often compare them directly to sandpaper grit (which is not the same), grit alone does not tell the full story.
Other factors—such as the sintering process, diamond quality, grain distribution, and even the backing material—play a major role. Our discs are the result of extensive testing, aimed at achieving what we consider the best possible disc for rough sanding and another for polishing. The same philosophy applies to our diamond files.