Thursday, June 19, 2008


Two natural stones under the electronic microscope

What was my excitement yesterday when the first images of two natural stones powder appeared on the monitor connected to a SEM (Scanning Electron Microscope)!

I had had the idea (more precisely the faint hope of a possibility) to observe stone powders under an SEM soon after I joined the institute where I am currently working here in Taiwan. The Industrial Technology Research Institute (ITRI) regroups many different labs specialized in domains as varied as material science, opto-electronics and medical instrumentation.

I had asked my friend Emma (more thanks to you Emma!) if she could arrange some time to observe the powder, but she had had so far a busy and tight schedule. But eventually the day came. I don't recall having seen many SEM images of stone powder, only 1 of which I am sure, in a Japanese book. And never had I had the chance to observe my own stones.

Before writing more, here is one of the image we saw. It is a black natural stone from Taiwan, which a close friend of mine estimates to be in the 10,000 to 15,000 grit when lapped with a diamond stone.

Taiwanese stone

Taiwanese black stone (grit ~10,000 to 15,000), 8000x



Japanese stone (Kyoto, honyama brand)

Japanese Stone from Kyoto (honyama brand, from Lee Valley) 4000x



60000x (notice the small holes?)

Stone powder preparation

I obtained the stone powder by simply lapping my stones with a diamond plate adding small amount of water. Both the stone and lapping plate were thoroughly rinsed with water prior to collect the slurry. The paste I got from the lapping process was then collected into a clean plastic container and left to dry.
The powder is then scrapped and deposited on a small metallic plate (which fits the SEM vacuum chamber) and covered with a thin, vapor deposited, layer of tin. The tin is necessary for non conductive material and it doesn't change the structure of the specimen.


Well I hope you can participate!
What stroke me the most is the that many particles appear like scale of a fish, as if some crystals in the stone had been cleaved. I wonder whether that is the action produced by the diamond plate. And that is what would provide the stone (particularly the Taiwan stone) a more pronounced cutting action.
Note also that on a larger scale (dimension), many natural sharpening stones can split into layers or strata. I wonder if the microscopic observation has any relationship with the mentioned property.
Further observations would be to look at the surface of the stone itself, that is flat and free from any slurry from the lapping plate. A whole stone will not fit in the SEM chamber, but I could break off a 1 or 2mm piece.
I would also be curious to observe a slurry in which metal particles are also included from a few sharpening strokes.
Also of course, I would love to observe different stones.
Now, let us make an analogy with planet exploration. If an imaginary earth observer was to point his telescope from a distant planet on the Gobi desert, he/she'd have a seriously biased idea of what earth is. Have you seen the scale of the photos? 1um to 20um... There is surely a lot more to be seen and discovered even for one particular stone.
And my friend said that a blade could also be observed...

The issue to these experiments is the cost. My friend accepted to do it for free the first time, but since her lab performs observations for other departments, it must charge the customer. The cost of using the SEM is about 80US$ per hour. An observation can be done in 30mn a the fastest, that is still some money that unfortunately I would rather spare for buying wood or for a trip to Japan.
If enough of you are interested in these observations, with each one sharing the cost, then let us decide of a stone to observe and conduct more observations.
One remark: with the SEM, we can not distinguish a chemical element from another, silicate from aluminum dioxyde...

Note on the images
I have no problem you copy these images and publish them elsewhere at the condition you mention their origin.

I would like to know where you got the "Taiwanese Black Stone", and if there is a web site I could Order one shipped to the US?
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