Is Silicon Carbide better than Aluminium Oxide for (kasumi) polishing?

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cotedupy

cotedupy

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I can do you a really pretty decent san-mai kasumi off any dirt cheap vitrified SiC block, far better than any comparable grit AlOx stone I know. @refcast can do it with powder. @inferno rates the Suehiro G-8 as one of his all-time-tip-top-best-synthetic-kasumi stones.

Is Silicon Carbide just better for this kind of polishing than Aluminium Oxide? And if so... why?
 
Comparing the the two, Aluminum Oxide has sharper "points" than Silicon Carbide, but is lower on the hardness scale than Silicon Carbide. Silicon Carbide has a tendency to fracture, further dulling the "points", and is harder and more brittle than Aluminum Oxide.
 
I know you are talking about stones but FWIW, I've done a lot of heavy duty thinning then refinishing on (mostly cheap) SiC sandpaper. Mostly stainless san mai but the contrast wasn't good. Not noticeably different to AlOx sandpaper. I distinctly recall having to squint to see the lamination line.
 
Nemo said:
I know you are talking about stones but FWIW, I've done a lot of heavy duty thinning then refinishing on (mostly cheap) SiC sandpaper. Mostly stainless san mai but the contrast wasn't good. Not noticeably different to AlOx sandpaper. I distinctly recall having to squint to see the lamination line.
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Yeah good point, I've not ever found any sandpaper to really to do contrast either.

SiC seems to do well when kinda worked down as a slurry, either from a stone, or as powder as in Refcast's version. Which probably ties in quite well with Mike's interesting info above...
 
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M1k3 said:
Comparing the the two, Aluminum Oxide has sharper "points" than Silicon Carbide, but is lower on the hardness scale than Silicon Carbide. Silicon Carbide has a tendency to fracture, further dulling the "points", and is harder and more brittle than Aluminum Oxide.
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TBH I didn't really expect to get any answers for the 'why?' part of my question, but that explains it rather well I think. Interesting stuff, which I didn't know before.
 
cotedupy said:
TBH I didn't really expect to get any answers for the 'why?' part of my question, but that explains it rather well I think. Interesting stuff, which I didn't know before.
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My theory is SiC fractures, creating loose grit. The loose grit then rolls, instead of digging in. Third body abrasion.
 
I have a set of loose grit i use for doing polishing. I think the progression is 80-220-500 in sic, then 1200 in aluminum oxide.

It just came with those four grits sold together i didn't purposely buy the 1200 in aluminum oxide.

Anyway, in use with the loose abrasive. I don't really notice that one abrasive does better than the other. The aluminum oxide is finer, because its a finer abrasive, but otherwise they seems pretty close to eachother in what they do
 
I have not had luck achieving any sort of decent contrast with sic or aluminum oxide powders. Tried from 60 up to 2000 grit. The result is most similar to sandpaper in my experiments with them.
 
deltaplex said:
What liquid are you using with them?
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I've tried water and mineral oil. I originally bought a pack of various tumbling grits from ebay and wanted to blend em to make like a synthetic kasumi mixture. But didn't work out as I had hoped.
 
I definitely got more contrast with loose aluminum oxide than i did with sandpaper
 
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