I have a black, hard Arkansas oil stone that's probably close to 100 years old (handed down from grandpa). The surface isn't flat anymore and it has some chips and dings from many years of service. It doesn't seem to cut very well too, and I'm guessing the pores are filled with dirt and dross. I've read about techniques to clean the surface (such as a good long soak in an oil dissolving cleaner and baking in a stove) and I had been planning to go at the surface with a diamond grit flat stone of similar width. Has anyone had any experience (good or bad) with rejuvenating an old timer like this?
Do you know of someone that works rocks into jewelry? Or a local rockbound club, or maybe a university/community college that has rock saws and 'lapping' wheels? A little time with a lapping wheel and the right lapping compound will dress your stone very nicely.
I can say with great certainty that baking out an abrasive stone can fail spectacularly. I tried once, setting it near the coals in an outdoor fire. After some time I heard a loud crack, and discovered my stone in about six pieces.
I have flattened other stones simply by sitting down in my driveway and rubbing the stone on the concrete with a bit of running water. May work for your stone, too. I use carb or brake cleaner to remove the old oil and crud
Was that a natural stone or a synthetic one, Grant? I've heard some say that natural stones may break from heat, but never a synthetic one (India or Crystolon). I've baked the latter myself on three occassions -- old stones that I bought at garage sales -- with no breaks, but with a very satisfactory cleaning of the stone.
I'm hesitant to try it with my valuable hard Arkansas stones, but other people have done it. Do you think that the uneven heating of the coals may have contributed to it?
My diamond blade tile saw has diamonds up the sides about 1 1/4". I would think that one could carefully touch the stone to the sides of the spinning blade and come up with a flat surface. That would depend, of course on the total size of the stone and the throat of the tile cutter.. One could mount the stone to the rolling tray so as to only shave off 1/16 or so on each pass. It's hard to say without seeing it, but I have seen cutting wheels that the diamonds run up the sides for quite a ways.
I put them in a steel baking pan lined with aluminum foil and stuck them in a cold oven, which I turned up to 275 deg. F. I left the first one in for around a half-hour; that wasn't long enough, as I found out later when I re-baked it for close to an hour and a lot more gunk came out.
One of those stones was badly glazed and it came out pretty clean the first time. After a year of use, with frequent oiling (I make honing oil from 10% motor oil and 90% kerosene), I baked it again, and it came out like it was new. I had to air out the house for a week, however, and to live in the doghouse for a while. d8-)
Those were old Crystolon (Norton's silicon carbide) stones. All together, I guess I've done this on five or six occasions with those three old stones. I've never let the ones I bought new myself get to the state where they needed baking. I just flood them with honing oil at the end of each use and wipe them off good with a paper towel. My fine India stones are still clean after...uh, maybe 50 years of frequent use.
Natural stones from Arkansas are alumina or emery (alumina with magnetite, so they're black), so a diamond hone will dress the surface. Don't do that until you've cleaned it, though. I'd start with hot soapy water, then rub vigorously with a good quality plastic eraser (in my experience, this removes surface gum and glaze), work it against a cheapo (dollar store) gray stone for a bit, and finish with a few strokes against a diamond hone.
I wouldn't try to flatten it, and a few nicks don't hurt the operation. Remember, only if the nick is as big as your bevel will the blade alter course going over it!
I use my natural stones with a little soapy water, and they don't seem to clog. Oil has never worked well for me.
Thanks Karl, this looks like a very interesting link.
And thanks to all for your suggestions and sharing of your experiences. I wasn't keen on baking an oily stone in the oven and I'm certainly not going to do it now. It's too cold up here (north of the 49th parallel) to try and air my house out for a week!
I have a number of concrete and stone saws (too aggressive) and the meanest diamond chip, angle faced "concrete planing" attachment I've ever seen... that bolts to a 7" angle grinder. I can't imagine what that bad boy costs at retail, but I was lucky to get it free at a local pawnshop 'cuz it was attached to a good Dewalt grinder I was buying and the pawnbroker didn't know what to make of the disk. It's designed for flattening uneven concrete prior to tile or wood flooring. It has so much mass that it acts like a flywheel when I spark up the grinder and you have to have a white knuckle grip on it until it finds its balance, once up to speed. It cuts like a demon but can leave a glass smooth finish with the proper technique. Absent a better method, I think I'll cobble together a jig of some sort so I can control the cut and keep the tool and stone in a parallel plane.
Since the stone is so old, and because of the sentimental value, I want to be careful with it and wondered if there was a better alternative. I think the diamond grinder will be the way to go.
Good suggestions. I was going to give it a wash with TSP or some similar degreaser. I hadn't thought of an eraser but it's worth a try.
There's some nicks on the edge that alter the face enough that I want to remove or reduce them. The face isn't nicked or gouged but it's not really flat. I wonder if it ever was? It almost looks like it was rough hewn and didn't get much finishing when it was first made. I know my grandfather didn't have much money to buy expensive tools just after the war (dub-ya dub- ya 1). It's possible he bought it as a "second" or some such thing. His skills more than compensated for mediocre equipment.
Oil has never worked well for me.
I never felt like oil did anything on this stone, but I hardly ever used it 'cuz it was a poor performer. I think it's dirty and glazed and I'm hoping it'll spruce up with some TLC.
First, a comment on the aggressiveness of the cut. A hard black arkansas is the last in the series of arkansas stones that you use to sharpen a blade. You would start with a washita, then a white and finally a hard black. The hard black is for putting a final mirror- finish razor-sharp edge on a blade. It removes very little material because of its fine grain. Your belief that it is not cutting well may be wrong if you are trying to use it for the initial sharpening.
There are two primary home-brew methods for flattening a stone. The first is rub it on a diamond hone of the same size or bigger. This is the more expensive option. The other method is to use silicon carbide grit or silicon carbide paper on a piece of float glass or surface plate. The stone is rubbed on the surface until it is flat. I have heard that using the grit is faster, but it will eventually wear a hollow in the glass plate. Using paper protects the glass. The silicon carbide appoach is slower than the diamond and depending on how much material must be removed may take a significant amount of paper or grit.
I would not use a wheel grinder to flatten the stone as I believe that it would be too hard to control and could possibly ruin the stone in a few seconds. You also need to consider the type of blades you are sharpening as to how flat the stone should be. If you are sharpening plane irons or chisels, the stone should be dead flat. If you are just sharpening your pocket knife the hollow is probably inconsequential.
I forgot to mention what I found to be the best method of cleaning sharpening stones. I dump the stone in my ultrasonic cleaner for a short period of time. After removing the stone from the cleaner I gently heat it with a hand-held heat gun. You can also set them out in the sun on a warm day.
The latter is the way I flatten a synthetic stone, but have you tried it with Arkansas stones? I didn't pipe up on this part of the question because I've never tried to flatten a natural stone -- because I've never had to. But it's an interesting question.
twolluver gave a good description of how to flatten which will also clean the stone. If the stone is natural it will have no open connecting pores and the glaze will be just on the surface so lapping with 90x silicon carbide grit on plate glass, cast iron, granite tile or any similar flat surface will quickly remove the glaze and flatten. If a lot of lapping is to be done psa mylar will protect the lapping surface and help keep the grit from rolling and crushing. The only truly critical tools that require flatness are chisels. Wide plane irons depending on their use, may also require a truly flat stone. Just a quick revision: two critical elements to a cutting edge, shape and keenness. Shape, dictated by use and materials, extremes are exemplified by a straight razor and a metal cutting tool bit, both may be equally keen, the keenness being determined by the degree of polish on the two surfaces that meet to from the cutting edge.
In lapidary circles, there is a machine called a vibrating flat lap. It consists of a big metal pan and plate mounted on springs with a motor and an eccentric weight .
It is used to polish cut geodes and stone slabs. You charge it with coarse abrasive, put your stones on it (weighted if need be) turn it on and come back in a few days to charge it with finer abrasive.
It would probably flatten a hard Arkansas stone pretty readily.
However, I cannot imagine a hard Arkansas stone getting that wallowed out, Washita maybe but not a black.
As a side note, I was taught to never use oil on one of these, it just clogs the surface. Always use water. If I had to clean oil out of one, I would probably boil it in lye.