How to tell grit of old stones

[Larry L]

I have several of my father's old stones. He was a barber and I learned as a youngster how to sharpen razors and knives (probably not properly). Other than feel, how can I determine the grit?

 

[willc]

If I am uncertain of the grit of a stone I take a knife that has a high polish on it and do a few passes and then check it with a loupe and that will show the scratch pattern pretty well.

 

[scdub]

Quick way to get comparative grits is to simply rub the stone lightly across your lips - they can detect grit better than most other body parts I’ve tried...

 

[garry3]

Are they natural stones. If so pictures would help with identification. Natural stones don’t have a grit rating and neither did the older man made stones or razor hones.

 

[Larry L]

Thanks for the input. The stones were probably natural since I am 80 years old and my father passed in 1961, so they would be quite old. I know one is two sided and another is in the original box and I believe it was marked corundum. I''ll have to check it out. I have a loop and will try all above usggestestions except I still haven't figured out how to post photos yet.

Thanks again,
Larry

 

[Obsessed with Edges]

Thanks for the input. The stones were probably natural since I am 80 years old and my father passed in 1961, so they would be quite old. I know one is two sided and another is in the original box and I believe it was marked corundum. I''ll have to check it out. I have a loop and will try all above usggestestions except I still haven't figured out how to post photos yet.

Thanks again,
Larry

The 'corundum' labelling indicates aluminum oxide, which has been around for quite a long time in sharpening stones. These would be manmade stones. It's possible that the 'corundum' grit itself might've been mined from the earth, implying a 'natural' grit could be bound together in what is otherwise a manmade stone. But for a long time now (for decades), the vast majority of aluminum oxide grit used in abrasives is synthetically produced from factory processes.

For some perspective, even the completely synthetic abrasive known as 'silicon carbide' (SiC) has been around for well over a century, invented in 1890. And when it was invented, it was touted as the next step up in performance from the previously-existing aluminum oxide ('corundum') abrasives of the era. The trade name 'Carborundum' was given to the new SiC grit, playing on the 'corundum' name for the aluminum oxide stones. So, the aluminum oxide stones have quite a long history and have been the most commonly found 'hardware store sharpening stone' for a very long time, even to this day.

It's also possible or even likely, the two-sided stone might be aluminum oxide. They're the most common type of dual-grit sharpening stone. But sometimes, cut slabs of truly natural stones (like so-named 'Arkansas' stones) are glued/epoxied together to make a 2-sided, dual-grit stone.

As for determing approximations of grit, I've found that comparing scratch patterns against those produced on a new, unused sheet of SiC wet/dry sandpaper is a good way to estimate the effective grit performance of an unknown stone. SiC sandpaper can be found in grits through a wide range (maybe 60 through 2000, at least), so it's handy for getting a feel for how each grit performs. I emphasize new sheets, because SiC grit will fracture and break down with use, meaning its effective grit performance becomes much finer, as it breaks down.

 

[catspa]

If there’s an auto parts store near you with a body repair department, they’ll have assortment packs of wet/dry paper.

Parker