Cleaning an Old Oil Stone

A fellow woodworker (Jeff Ranck) reported the following experiences to me that might be helpful on cleaning some very badly clogged oil stones:

"I tried the cleaning process you recommended, no go. I just couldn't seem to get anything very clean. I also noticed that the stone was not flat. I lapped the stone against some sandpaper on a flat granite tile. That cleaned the faces up well. 

"In an old book, they talked about cleaning oil stones (after they had gotten really really bad) by putting a rag into a pot, adding some soap and boiling the stone. The rag keeps the stone off of the hot spot of the stove so it heats uniformly by the water (no cracking). The oil floats off as the heat opens the pores and the soap acts on the old oil. Sounded like something to try. However, my wife was less than enthusiastic about me boiling a greasy rock in her pans. 

"Meanwhile, I read somewhere to try the dishwasher. Light-bulb flashed on. Put the stone in the dishwasher with a load of dishes (when my sweet wife was not home ) and wow! The stone looks brand new. No residue as far as I can tell (we don't use any type of rinse agent or anything)." 

" A through C show the stone before I started to clean it. You can really tell the side my great grandfather used, it is almost black.

"D shows the best I could clean it using the methods you talked about and pretty much everything that was on my shelf that I thought might help clean the oil. Pretty good, but still a lot of stuff on the stone.

"E shows the true color of the stone after I started to lap it. Note how dished it is.  This is why I think it is a softer stone like a soft arkansas or washita.

"F shows the stone after running through the dishwasher. Standard dishwasher soap no rinse agent. Let it cool before you put it on anything cold. When I thought about it, it makes sense. Dishwasher soap is designed to dissolve grease and oils. The hot temperatures of the dishwasher should help open the pores of the stone and the water
flushes the stone really well."

Thanks goes to Jeff for sharing his experiences!

I was encouraged by his results, so decided to give it a run myself.  However, since LOML wasn't about to let me try the dishwasher method,  I decided to give the boiling method mentioned a shot. I had an old oilstone of unknown type I had purchased for a few bucks (the box it was in looked well made, so I figured somebody thought it was worth something once upon a time), and threw it in an old pan on top of some rags and and boiled it  in water and both some dish soap and some dishwasher soap (some of which contain phosphates, which aid in breaking up the oil) for about 15 min. or so:

You can see the oil coming out and darkening the water around the stone. The rags are to keep the stone off of the hot bottom of the pan, and keep the resulting temperature differences from cracking the stone. If you're wondering about smell - the whole time I was boiling it I was reminded of being in my grandmothers' kitchen - the smell was the same, and pleasant - at least to my mind. She used an oil stone in the kitchen... LOML didn't complain either, so it didn't bother her, either.

I then let the thing cool on the stove before I removed it so it wouldn't crack then, either. The results were quite good! After boiling the oil out, I put some 60 (then 100) grit sandpaper on the jointer bed and sanded the stone flat. Here's the progress shots:

You can see the marked improvement. Prior to cleaning, this stone was clogged about to the point of uselessness. Now - I needed to test it out. I found an old throwaway chisel:

Nothing spectacular about this old thing. Next was to sharpen it. First - the stone seemed pretty fine, so I ground a new bevel on it, then tried it out on my new 'old' stone, then stropped it on leather charged with honing compound - here's the progress shots for each of those steps:

The edge in the center is straight off of the stone (hollow ground, so not in the center, just the ends of the bevel!). There's a satin sheen to it, not too much more coarse than my translucent arkansas stone gives, so I'm pretty confident this is an arkansas stone - it's grit says to me soft, but there was very little dishing of the stone, which I would think odd for a stone of this age. 

To try it out after stropping it, I took an old piece of ash and gave the end grain a go (and try as I might, I couldn't get a good shot of it - sorry!):

Cuts through the end grain cleanly and easily. So - for about $10, I now have a great stone!

I think it's easy to see here that many old oil stones can be recovered.  Before cleaning, this stone really was pretty useless - it took forever to grind an edge with it, and I was unsatisfied completely with the results.  After cleaning, the edge above took me about 30 seconds on the stone - before I cleaned it, it would easily have taken four or five times that amount of time.