Mono-crystalline vs Poly-crystalline Synthetic Diamonds
Here are some answers to common queries about the differences between Mono-crystalline and Poly-crystalline synthetic diamonds and emulsions containing these two different abrasives, specifically surrounding the context of stropping.
Please remember that this information is not intended for every heavy industrial or high-pressure tooling application these particular diamonds may be found in, where they both have the potential to behave very differently.
Mono-crystalline Characteristics
Mono-crystalline synthetic diamonds are made in two ways: a High Pressure-High Temperature (HPHT) process and a Chemical Vapor Deposition (CVD) process. They’re known to be practically defect-free and are single-crystal structures more likely to resemble naturally occurring, non-synthetic diamonds, which is one of the reasons they are so popular.
Mono-crystalline’s single-crystal structure makes them larger with much more predictable, defined fracturing planes and they are noticeably longer-lasting. Having naturally occurring cleavage planes in their crystal structure allows them to chip in a controlled way along these fracturing planes, breaking up during the course of normal use.
This micro-chipping renews the abrasive function of the diamond’s sharp, defined cutting edges, refreshing them so they act like new diamonds and quickly remove steel while still maintaining consistency in size to their specified micron rating.
Due to this process they are known to have excellent cutting performance, giving your blade’s edge the ability to get, and hold, its crisp bite for a long time. They are especially good at producing a more toothy, clean, linear micro-scratch pattern on your bevel, creating a competently refined, thinned-out apex with a magnificent mirror polish and bite.
Mono-crystalline diamonds aren’t just found in high-quality stropping emulsions. They are also commonly used as the sole abrasive on most diamond sharpening stones produced by many of today’s top-tier manufacturers due to their cutting longevity and overall performance.
Poly-crystalline Characteristics
Poly-crystalline synthetic diamonds are manufactured solely in laboratories, meaning they are more expensive to produce than Mono-crystalline diamonds. Because of this they are comparatively less common.
These diamonds are characterised by clusters of countless incredibly small diamonds bonded together to form complex, random, unpredictable shapes and cutting edges—similar to miniature fragments of shattered safety glass.
They’re known to cut fairly aggressively at first due to their inherent extreme hardness. Their multi-faceted structure means they have multiple cutting edges that are multi-directional, allowing a single diamond particle to bite into the bevel multiple times during a single pass. The downside is a less refined stropped edge that may produce somewhat unpredictable results.
In theory, these harder bonded diamond facets are more friable, breaking apart over time into new, smaller cutting particles. These renewed edges produce irregularly shaped, finer diamonds.
In practice, however, they are extremely tough—too hard-wearing to fracture significantly under the pressure applied by normal stropping methods.
Due to their hard, small, wear-resistant particles they provide a softer progression and leave a pronounced, smoothed-out bevel. After only mild use, their small size means material is lost fairly quickly as the fine fragments become dislodged from the strop’s surface.
It must be noted that they also produce an extraordinary polished edge.
These diamonds can also be found in applications such as stone masonry, jewellery manufacturing and associated tooling, where high hardness and wear resistance are preferred.
Summary of Their Main Differences
Mono-crystalline Summary
- Each particle is a single, solid crystal with defined cleavage planes and naturally sharp edges.
- As they wear during stropping, they fracture along their natural planes, constantly exposing fresh cutting edges.
- The edges cut cleanly into hard steels, producing concentrated, linear scratch patterns.
- Excellent for long-lasting, fast and consistent material removal.
- Produces refined mirror-polished edges that retain a crisp bite over time.
Poly-crystalline Summary
- Clusters of countless microscopic synthetic diamond particles bonded together with multi-directional cutting edges.
- They lack larger fracturable cleavage planes but, under very high pressure, can break down into even finer particles.
- Theoretically creates new micro-edged fragments that smooth and polish steel rather than aggressively refining it.
- Ideal for lighter touch-ups and extremely high mirror finishes.
- Produces polished cutting bevels with a smoother overall surface.
Final Thoughts
There is no doubt these two synthetic diamonds represent the pinnacle of micron abrasives used for stropping. Both are capable of producing exceptionally refined edges with highly polished apexes.
Ultimately, the choice comes down to your budget and personal preference. Mono-crystalline diamonds provide fast, clean-cutting particles that create a refined progression, linear scratch pattern, crisp bite and remarkable mirror finish.
Poly-crystalline diamonds offer smaller, harder, wear-resistant particles that are gentler on your edge, producing a softer progression, a multi-directional scratch pattern and exceptionally polished, smoothed-out bevels.
