We recently added Spyderco Medium, Fine, and Ultra Fine stones in custom 1×4-inch and 1×6-inch sizes for use with several sharpening systems. On its own, that wasn’t particularly unusual, but it soon led to a friendly debate about the Fine and Ultra Fine stones.

For years, there has been a theory that the Spyderco Fine and Ultra Fine stones are actually the same stone, with the only difference being how their surfaces are finished.

My view is slightly different. I believe the Fine and Ultra Fine stones use the same basic material and a similar formulation, but contain different abrasive sizes. Based on their finishes, I consider the Fine to be around 2K grit and the Ultra Fine closer to 4K grit. That would help explain both the difference in the finished edge and the price of the stones.

Konstantin from Gritomatic sees it another way. His opinion is that the stones are completely identical, including the abrasive size. According to his theory, the only real difference is the surface texture of the stone, which changes the scratch pattern left on the steel.

Naturally, this turned into a challenge.

I was given five Spyderco Fine and Ultra Fine stones to see whether I could correctly tell them apart. And, of course, we couldn’t do a test like this without putting something on the line. The wager was a bottle of Russian vodka against a bottle of Kinmen Kaoliang.

Both Ideas Make Sense

Before getting into the test, it’s worth saying that both theories are reasonable.

The surface finish of an abrasive can certainly affect how it cuts. Natural stones containing quartz, for example, can be conditioned to have a rougher or smoother surface. This can change the depth and appearance of the scratches they produce.

We see similar effects with dressing stones used on Tormek wheels. Raising a slurry with a diamond plate, nagura, or conditioning stone can also change the way a synthetic sharpening stone feels and cuts.

My argument, however, is that surface texture mainly changes the aggressiveness of the stone. As long as no additional abrasive is introduced, I’ve generally seen the final scratch pattern remain consistent under magnification.

So, there was only one way to settle the debate: look at the stones and edges under a microscope.

Setting Up the Test

All microscope images for the test were taken using a Dino-Lite AM4113T.

For reference, the photographs include measurement bars showing 1 mm at 20× magnification and 0.2 mm at 200× magnification. Enlarging the images makes these scale references easier to see.

With the stones ready and a bottle of Kaoliang on the line, it was time to begin the test.

Konstantin sent me five stones and confirmed that the group contained at least one Fine and one Ultra Fine stone. Before moving on to the actual scratch testing, I tried a few simple ways to identify which stone was which.

To be fair, I had a slight advantage. I already had my own Spyderco stones available for comparison, including cut, uncut, processed, and unprocessed samples.

Starting with Stone Thickness

The first thing I checked was thickness. The Spyderco Fine stone tends to be slightly thicker than the Ultra Fine, so my thinking was simple: the thinner samples were more likely to be Ultra Fine stones.

Based on thickness alone, I identified stones 2 and 5 as Fine, while stones 1, 3, and 4 appeared to be Ultra Fine.

Of course, Konstantin would probably expect me to check something this obvious. So, clearly, I couldn’t make my final decision based on thickness alone.

Time for the Microscope

Next, I moved the stones under the microscope.

The first round of images was taken at 20× magnification and compared against my own known Fine and Ultra Fine stones as controls.

At first, the results looked fairly easy to interpret. Based on the surface appearance, stones 1, 2, 4, and 5 looked like Fine stones, while stone 3 appeared to be Ultra Fine.

But there was another problem.

Konstantin knew I had access to a microscope and would almost certainly inspect the stone surfaces. It was possible that the surface finishes had been changed or conditioned to remove the obvious visual differences between Fine and Ultra Fine stones.

So once again, I couldn’t confidently make my choice based on the evidence in front of me.

The real scratch test was becoming more important.

 

Onto the 200x, which would reveal even more secrets. Results were slightly different, with the 1,3,4 and 5 stones being fine and stone 2 being UF. Clearly this was starting to get dizzying…So I could clearly not choose the cup in front of me.

So seeing as the stones were lapped before I got them, and the control pics were different from what I was seeing, we lapped everything again – both my controls and the stones from Konstantin to see if that would even the field more. I spared you the 20x pics and jumped straight to the 200x. Results were 1,2,3 and 5 as Fine, and 2 and 4 as UF, so I could clearly not choose the cup in front of him!

So enough games – it’s time to drink. Last test was the all out scratch test. I started off with a control 600 diamond scratch, and then make parallel scratches against the control stones. Each time I went to a new stone, including the on the controls, I reset the askew angle on the 600 diamond to erase all traces of the previous scratches so we could see a true finish. Here the results are a little more visible, ending with stones 2,3,and 5 being Fine and Stones 1 and 4 as UF. Quite a different story from the previous tests.

 

So in conclusion, I say the Fine stones are 2, 3, and 5, while the UF stones are 1 and 4. This was a tough test, to be honest. I’m glad we were able to have fun, I will post the actual grits from Konstantin when he reveals them.

Either way, it was better than getting involved in a land war in Asia. I think it’s time to drink some alcohol! Inconceivable!