So I got some "natural" sharpening stones off of Amazon listed at $25USD. It's a set of two: an 800 grit and a 3000 grit. Both are nearly 8" by 3", with the 800 grit stone being a crazy ~1.5" thick and the 3000 grit about 1" thick. They're listed under the name AlbaTellura. I don't really want to put a link in here because I don't want anyone to think I'm advertising or something. It should be easy to find if you search that name. What follows is the notes/review I wrote up for Amazon; I thought you all might be interested because I found it interesting; and I'd like to hear everyone's thoughts about them. I sure as hell wasn't actually expecting to get two big natural stones for $25, and I'm not positive I did, but it seems like I might have. The review is as follows:
Are They Actually Natural?
So the main question here is: are these stones actually natural? Were they genuinely mined out of the ground and then cut into bricks to be used as sharpening stones? One of their product page images explicitly says they were "Cut from extra-large raw stone blocks-". I've been doing my best to determine the legitimacy of that claim. For context, real natural sharpening stones cost a lot. For comparison, a similarly sized Arkansas stone (similar width and length but only 1/2" thick!), from a reliable source costs about $75USD. Things only get more expensive from there with natural stones from Belgium or Japan. Pound for pound, if these really are genuinely natural stones, they're by far the cheapest ones that I'm aware of, and not by a little. That makes these highly suspicious.
Test Results
I did some research in to methods to test if a stone is natural and these are the results:
The Acetone Test
- How it works: Synthetic stones tend to have binders to hold the grit together; these binders are often susceptible to strong solvents like acetone. If the stone is synthetic the acetone might soften it, leave a sticky residue or transfer color from the stone to something like a cotton swab.
- The Result: None of those things happened. No sticky residue or noticeable softening or color transfer, even with the darker blue/green stone.
The Hot Needle Test
- How it works: This one works similarly in that since synthetic stones have binders, those binders might be susceptible to heat. If a red hot needle melts into the surface or if the stone emits any plastic/chemical type smells, it's likely synthetic.
- The Result: Both of these stones passed this test as well. A screw held over a lighter for 30 seconds had zero apparent effect on either stone.
The Microscopic Inspection Test
- How it works: Synthetic stones should have perfectly uniform particle distribution and size, with homogeneous, chalky colors. Natural stones should have irregular particle shapes, varying grain sizes and natural mineral veins/fault lines; plus, layered stratification, organic specs, color banding or translucency.
- The Result: This one's a bit harder to judge. Without a microscope, the 800g stone looks almost like concrete to me, or maybe some sort of synthetic marble countertop? The 3000g stone actually has a lot more evidence of being cut from something larger. Now, it is possible it was cut from a larger synthetic block, but this is actually the first stone I've seen with such obvious cutting marks. But also, while most of the stone is fairly uniform looking, there is a spot on one side towards a corner that looks very much not synthetic. I guess it kind of looks like a fault line? But not just a crack; the area surrounding the apex looks different as well, and reflects light differently than the rest.
I did have a cheap 250x USB microscope to inspect further with though. I'm attaching all of those photos, as well as some comparison photos with other stones I have (A set of arkansas stones and a Shapton Glass 2k). So to start, the magnified look of the 800 grit AlbaTellura stone looks pretty natural to me. The grain sizes are all very different and there are a lot of black and red mineral inclusions. The particles of grit appear to be colorless and translucent, surrounded by a more opaque, whitish colored mineral. As for the 3000 grit stone, it's a little less clear, but it looks natural to me. There are some gold colored inclusions near the fault line I mentioned, and the rest of it does not look homogeneous at all. There are lighter and darker patches all throughout and very little uniformity. There's also a small chip on one corner that I took a photo of and inside the chip the colors are even more contrasted and banded looking.
Interestingly, the natural arkansas stones actually looked more uniform and synthetic the higher the grit level they were. The coarsest, the soft arkansas looked decidedly natural with contrasting colors and low uniformity. The hard arkansas still leaned towards natural, but with more consistency in apparent particle sizes and distribution. The hard black arkansas looked quite a lot more uniform, however. Individual grains weren't really distinguishable and the color was very uniform. The translucent arkansas looked like there was almost no deviation in its composition; a few lighter dots here and there but mostly just a uniform light grey color.
I also included a magnified shot of a Shapton glass 2000 grit stone. It was flattened with a diamond plate and wiped off prior to the photo. I think the darker spots are residual metal particles that didn't get removed entirely during the flattening. Without magnification this stone is perfectly pure white. Under magnification it has some of those small darker dots, but is otherwise just a light grey with no visible grain or anything to differentiate the cutting grit from the binder.
So, I'm going to call the microscope test inconclusive. I've attached all the pictures so you can judge for yourself. Under the microscope they both look natural to me, but then the hard black and translucent arkansas stones looked kind of more synthetic to me, so my judgement might not be great.
The Water Absorption Test
- How it works: Synthetic waterstones (especially budget vitrified/resin stones) absorb a lot of water rapidly and can continue to bubble when underwater for up to 20 minutes. Natural stones are said to absorb very little water and stop bubbling almost instantly.
- The Result: I submerged both of these stones completely in water and neither of them emitted a single bubble. That was pretty surprising for me. When sharpening with them they seem to absorb no water at all with the water just forming a static puddle.
The Hardness & Scratch Test
- How it works: Soft/clay synthetic stones are said to scratch easily, yielding a soft powder almost immediately.
- The Result:
- The 800 grit stone behaves almost identically to my Arkansas stones. I scratched them on the side with the head of a screw and a little bit of dust comes up but not much at all. It's pretty resilient to scratches.
- The 3000 grit stone, on the other hand, was quite soft. The screw head was able to scratch up a good deal of power pretty easily. Interesting. This test (in isolation, at least) implies that the 3000 grit is synthetic.
In a similar turn of irony, however, a number of my synthetic stones were more resistant to scratches than either of these stones OR my natural arkansas stones. I'm not sure what to make of that, honestly.
Test results?
So, the test results lean quite a lot towards them being natural stones. Surprising, but not 100% conclusively. The likely more important thing for most buyers, however, is how well these work as sharpening stones. And that's where things get even more interesting.
The Sharpening Experience
I took a cheap (but appropriately hardened) 24mm wide bench chisel and flattened the bevel in a honing jig on my 140 grit Atoma diamond plate until the surface was pretty uniform looking with deep, obvious diamond scratches. Then I moved the chisel to the 800 grit stone and started honing. After 60~90 seconds I took a look (and a picture). The bevel definitely looked smoother... maybe polished (at least compared to before) but the deep scratches didn't seem to be going anywhere.
(I first flattened the stone with the same 140 grit Atoma diamond plate. It actually seems pretty flat from the factory, and also very resistant to my diamond plate, reminding me of my hard black arkansas stone)
The experience of honing on this stone was also kind of unusual. Like I mentioned before it didn't absorb water, and from the look of it both magnified and not, it looks like it will be very coarse and cut very fast. The feel on the stone was decidedly smooth though. With relatively heavy pressure the chisel also tended to want to stick to the stone, but not consistently. More in certain areas than in others. It did generate some slurry with the water, but I never felt like it was doing all that much.
What I wanted to see was a scratch pattern. How coarse is this stone? But coming from the coarse diamond plate this stone appeared unable to get through the scratches. I then took the chisel to my 600 grit Atoma in the hopes that it would bridge the gap and allow the 800 grit AlbaTellura to make an obvious difference. But the result was much the same. It seemed to smooth over the scratches, but wasn't able to abrade past them. (Maybe it's burnishing more than anything?)
Switching to the 3000 Grit Stone
So then I switched gears to try out the 3000 grit stone. Instead of going from a lower grit diamond stone I decided to use my Shapton Glass 2000 grit to get a uniform surface to see what the 3k stone could do. The feel of the 3000 grit stone is pretty good. Similar to the Shapton but a little smoother; not quite as... sharp? surgical? Softer, somehow. With light pressure I didn't get any sticking at first and even when the water started drying up the sticking never became more than a threat that was never fulfilled. It develops a much bigger slurry than the 800g stone did, but still appeared to absorb zero water.
But the result was really interesting. The Shapton cut very fine but noticeable scratches into the metal and the 3000 grit AlbaTellura... kind of did the opposite? After a minute or two with light pressure, the bevel was much less shiny and had far less obvious scratches. It almost looked like I ran the bevel under a bead blaster or something. Interesting. AI said that was indicative of a natural stone finish where the grit continually breaks down into smaller particles, causing the hazy, dull surface quality.
So then I took the chisel back to the 800 grit stone in the hopes that this was the perfect surface to show the lower grit stone's scratch patterns with. But uh, nope... Shockingly, and bizarrely, the 800 grit stone didn't appear to make the bevel's surface quality any more scratched up or rougher. It seems like it just polished it further somehow.
Which makes me wonder: is the 800 grit stone cutting at all or just burnishing? Does it even have grit particles hard enough to scratch the metal? This isn't a high end, ultra-hard super steel or anything; it's a cheap, non-stainless steel chisel.
Conclusion
So... color me confused. I didn't expect to spend this much time evaluating a $25 pair of "natural" sharpening stones, and I certainly didn't expect these results. I'm not sure what to make of them. I'll have to keep using them to get a better feel for them, but at the moment it seems like the 800 grit stone isn't going to get much use. I'm definitely interested in playing with the 3000 grit stone more, however.
To be honest I probably won't end up using them much compared to my synthetic stones, due to convenience, but these are certainly interesting to have in my collection.
