Thread: Ceramic stones.

Anyone know what Ra 12 means as it pertains to hardness of ceramic?

Surface roughness. RA 12 means no more than 12 microinches (peaks / valleys) over a given length. Has nothing to do with hardness.

I think Ra (radiography) refers more to finish than hardness. One reference: http://www.honestoncasting.com/quality.html

Originally Posted by DistortedPenguin

Surface roughness. RA 12 means no more than 12 microinches (peaks / valleys) over a given length. Has nothing to do with hardness.

Can you be more specific? Is this good, bad?, as it relates to using as a hone.

Originally Posted by jimk

Can you be more specific? Is this good, bad?, as it relates to using as a hone.

An Ra value of 12 is equal to about 300 Grit (US) so the answer is no. Are you sure it's an RA 12? The stone should feel very rough if it is.

Also note that if your stone is marked with an RA value on it then it was more then likely intended to be used for large metal applications like sheet metal panels. Could still be used for a razor but at around 300 US Grit I don't know why.

Originally Posted by DistortedPenguin

An Ra value of 12 is equal to about 300 Grit (US) so the answer is no. Are you sure it's an RA 12? The stone should feel very rough if it is.

OK, long story short, I hope. I work at a power generating station. Some years back we used ceramic stones measuring 6"x2"x1/2" to line some high wear areas inside equipment. I have one of these stones that I mounted on a hardwood block. It's surface is baby butt smooth and as hard as well...ceramic. I've used this stone some in the past when honing knives. But just don't care for it for that use because of it's extreme hardness and surface smoothness. Yesterday I e-mailed Coors Ceramics and it was they that told me Ra12. The stone itself is not marked with anything. Anyway I got to thinking that since it's as hard as my teenagers head, well how about "razors".

I think Coors gave some bad info. If you've hones knives then you know as well as I do that if it was an RA 12 which is 300 grit it would eat the hell out of the blade.

Originally Posted by DistortedPenguin

I think Coors gave some bad info. If you've hones knives then you know as well as I do that if it was an RA 12 which is 300 grit it would eat the hell out of the blade.

Yeah, I agree. I've been sharpening knives and broadheads for as long as I can remember. Used to make pocket money a long time ago in a land far away puttin' an edge on KaBars and bayonets. I've never sharpened razors though. This ceramic stone and a surgical black arkansas that I have might work though.

Find something disposable that scratches easy and have yourself a look at the scratch pattern. If it's 300grit, it's going to be very easy to identify as too rough for use on razors. Even if it is, keep it. It'll be good for working out chips in a matter of a minute or two.

Surgical black I believe is in the 2k range. It's not atypical for decent quality triangles to use them. I wouldn't use it as a finisher for a razor. It will be shavable, but certainly not comfortable.

Edit: checked on blacks and I'm finding them in 900-6k range, so apparently they vary a lot. If it's a really fine one (5-6k) it could make a decent enough finisher. Especially if followed with Chrox before stropping.