Geological Specimen Supply
Hard gray shale - Inyo range, CA
This was a sample that Rudy had kicking around that he thought I might like. It is a siliceous shale. Silica is good and sharp. I DO like it! He was right.
|Surface #1 composition is uneven, with the darker 1/2 being more dense and slower wearing. Size is about 150-70-15 mm.|
|Looking at the side, you can see that the layers of sediment are not perfectly parallel with the working surface. If I can get a thicker sample, I will lap the surface planar.|
|Side #2 is uniform in overall composition, but has inclusions of soft, rusty material. It doesn't scratch, but does wear unevenly.|
|Starting from P1200 grit diamond, lamination barely visible.|
|30 seconds and diamond scratches look to be gone. Lamination line is sharply defined.|
I am trying to get one of these shales that is bigger and of a more consistent composition. It's on my wish list. For a first shot and a guess, this is a really incredible stone. It is soft, so it wears pretty fast, but not any faster than my Tanba?, really. I want a really big one so that I don't have to worry about it wearing out. And to be clear, these were not intended to be sharpening stones, they are teaching aids. That they work at all is great, that they work REALLY well is amazing! I may sell Tanba?!
I use a DMT duo-sharp fine/x-fine because it is somewhat of a familiar standard for hobbyists and because it is flat-ish and stays that way, but as I do these comparison tests, I end up polishing blades way more than I otherwise would. THAT'S when you see how deeply diamonds scratch, even well worn ones. I plan to experiment with using a kanaban, but if that doesn't seem like a fit for me, I'll be getting an Atoma diamond plate, not another DMT.