Old oil stones are often covered in gunk, so much so that it can be hard to tell what they are. I’ve had some that were so bad that even after scraping as much gunk off as I could, I still couldn’t even tell if they were natural or man-made.

I have no idea how they manage to get as filthy as they do.

This is a recent oil stone I’ve acquired:

Compared to most, this one isn’t too bad. The Norton logo is still visible, and it’s easy to tell it’s an India stone.

If a stone isn’t too bad, like this one, using it will often be enough to soften and clean off the gunk. That doesn’t always work, and it’s not always ideal, especially if you don’t know what the stone is.

Luckily, they’re fairly easy to clean. The easiest way I’ve found is to soak them in hot water with a dissolved dishwasher tablet. I suspect any kind of degreaser or soap that removes grease should work, but dishwasher tablets work well for me.

After 12–24 hours, rinse and wipe the stone down. If the stone is still dirty, repeat with fresh water and a new dishwasher tablet. It normally takes 1-2 soakings to get the stone clean.

Caution: Some man-made stones, including India stones, are prefilled with oil or grease, so you need to be careful not to remove the prefill. I’ve yet to have any issues, but I also check every 12 hours with man-made stones and stop as soon as they’re clean.

This is the result of two 12-hour soakings:

Not quite like new, but a lot cleaner than it started, and it works great.

Now it just needs a box.