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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.


Additional Commentary

This came from a fellow woodworker:
I've done a few of these myself and am always happy to bring a stone or slip back from the tar pits. The difference is that I add about a teaspoon of TSP (trisodium phosphate) to the water in a stainless steel or enameled pan and use pebbles instead of rags. Instead of cooling in the water I immediately remove the stone and plop it into a big deep tray of very warm sawdust (which I use to dry metals fresh out of hot pickle). The TSP (you could use di and mono as well, but TSP is easier to find*) really holds onto the oils and the hot sawdust sucks up both oil and water, leaving (to my eye) a cleaner surface free from residual emulsified oil. A final scrubbing with harsh detergent (more TSP - wear gloves), and the stone's ready for flattening on a diamond lap (or whatever).
Note:  TSP is not always TSP, anymore. Hardware stores often carry boxes of what's called in big letters "TSP", but then it says "Phosphate Free", which is fairly misleading, so read the label. If it's phosphate free, forget it and find another detergent or hold out for the real thing. Come to think of it, real TSP used to be a component of dishwasher detergent, which is why that may work well for people where TSP isn't banned yet (not particularly good for the environment).
When asked "I can see where the hot sawdust is also a good idea to wick out water, but wonder how you heat the sawdust. In the oven? what temp? how long?" he continues:
I'm eclectic. I've used a metal box wrapped in strip heaters at a silversmith's workshop. I'd say it stayed around 170F but couldn't be sure. You want it warm enough to drive off the moisture in the sawdust and so as to wick up pickle, etc., from the silver, copper, whatever, but not so hot as to brown the wood. Certainly nowhere near the flashpoint. I've used a turkey pan on top of the woodstove (in Massachusetts), and I've also used an iron skillet on a regulated hotplate and a large crockpot (on low). This stays around 150-160F, which is all right as long as you're not dipping a lot of metal (or stone) at one go. BTW, the sawdust of choice was always boxwood, and not ground like flour, but coarser, more like cornmeal or grits, or coarser still. Maple works, too. And kitty litter (bentonite), but be sure it's 'fresh' before you warm that, heh.


Also - this from another woodworker:
I faced a similar issue with a stone I bought (maybe $8.00 at most). Anyhow it was a light tan color with several darker streaks and very clogged.
I tried various methods, including sanding and using loose SC particles, but to no avail. This past weekend, figuring that I wouldn't be out much if it wouldn't work, I tried some oven cleaner on one side of the stone and it worked wonders! Lifted decades of oil out, and leaving a very smooth and hard slightly off-white colored stone.

Thanks again!

You can see from the findings of no less than 4 different people there's more than one way to skin this cat, and do it successfully. 






All very interesting.  I have a number of old stones I was ready to throw out.  I'm going to try several of the suggested methods (except the dishwasher methods _I value my life too much!.  The baking soda method looks like the easiest, so I'll try that one first.
Flattening the stones is another story.  Maybe Santa will bring me a diamond stone for Christmas.  Some of my stones are badly dished in.  Any more suggestions?


Some of my stones are badly dished in. Any more suggestions?

Well, if they are too badly dished, then there might not be enough left of them after you flatten them - in that case I would leave them alone and use them for curved tools like gouges and what not.

However - if you have a belt sander (especially a stationary one) with a coarse belt you aren't too worried about - that works about the most quickly to flatten a curved stone.  After that if you want it flatter yet just use a medium on a flat surface, such as diamond paste on a granite block, or sandpaper on glass...

Also, it's amazing how well a concrete block works (at least sometimes).

Good luck!



Sorry, I accidentally put this in the wrong article:

So I'm re-posting it here where it's supposed to be.
Hey, thanks for the great article! I'm new to knife sharpening. I just picked up a mysterious Norton two-sided brick, along with an old "Buck knife sharpening kit" which had a white Washita and a translucent Arkansas in it along with petroleum oil. I also had a cheap arkansas, a cheap diamond sharpener, and a piece of a flyback transformer core from a CRT TV, which I found useful for polishing to a mirror edge quickly.
All these just went in the dishwasher, and I'm waiting for them to dry. 2 things interest me:
#1: In the DIY electronics world, people submerge various things in oil, or shellac, and then connect it to a vacuum pump. The pulls all the gases out of the oil, and it also sucks the oil deep into the object submerged. I'll bet this could be done to great effect on sharpening stones. Perhaps one could repeat this process with various weight oils or liquids to clean the stone deeply, and it may make it easier to convert from oilstone to waterstone and vice versa.
#2: I wonder if it is dangerous if metal filings are pulled into the stone and rust. If a stone is saturated with water after being used, then maybe this can happen. I don't know whether you can remove rust from the surface of a stone without a grinder.