To be clear, it is a type of sharpening stone I will discuss that is known by a variety of names. The two examples of this type of sharpening stone in the photograph are known by the names Gabriella and Giuseppe.
Only kidding. Or am I?
But seriously, these two stones, depending on various times and places throughout history, have been referred to as Turkish Oilstones, Levant Sharpening Stones, names referring to different locations in the historic Levant, such as Syria, Israel, Palestine, Lebanon, Jordan, parts of Turkey, Greece, etc.
The stones in the photo were mined in Crete, and though there are varied opinions whether these Cretan sharpening stones are identical to historic Turkish Oilstones, I have read many have found them to perform similarly. Having not had access to any other stones of this type, I have no opinion on the matter.
I only learned of this type of sharpening stone about a year ago. Though once in common use in many parts of the world, these stones are currently little known in the United States. I was only able to find one source carrying them in the United States (the small one) and the larger one was shipped from a tool merchant in Europe. I wonder if a customs agent was perplexed as to why someone would ship what looks like a worn old cobblestone across the Atlantic!
Here is a reference to this type of stone from “Turning And Mechanical Manipulation“, by Charles Holtzapffel (1856)
“The Turkey Oilstone can hardly be considered as a hone slate, having nothing of a lamellar or schistose appearance. As a whetstone, it surpasses every other known substance, and possesses, in an eminent degree, the property of abrading the hardest steel, and is at the same time of so compact and close a nature, as to resist the pressure necessary for sharpening a graver, or other small instrument of that description. Little more is known of its natural history than that it is found in the interior of Asia Minor, and brought down to Smyrna for sale. The white and black varieties of Turkey oilstone, differ but little in their general characters, the black is, however, somewhat harder, and is imported in larger pieces than the white.”
The examples of Cretan sharpening stones I have both contain fissures, small voids, cracks, and other irregularities. From what I have read, this is typical for this kind of stone. These are natural stones, so rather than thinking of them containing flaws, I think of them as a remarkable substance produced by nature with all the complexity of anything else produced by nature.
These stones are porous, and traditionally, a new stone would be soaked in olive oil for several days to permeate the stone before use. In modern times, some prefer using mineral oil rather than olive oil.
This type of stone also works very well with water as a lubricant, and that is how I choose to use them.
A remarkable quality of these stones is the ability to serve as a moderately coarse sharpening stone as well as a stone fine enough to produce an excellent working edge. I can bear down hard with a chisel, plane blade, or knife without damaging the stone, and the bite of the stone removes metal very quickly. Lighter pressure produces a finer edge.
In addition to how much pressure is used, the surface of the stone can be quickly abraded using another coarse or fine stone, and this both changes the quality of the sharpening surface and creates a slurry of stone particles and water of different consistencies. In the photo, sitting patiently on top of the two Cretan stones, are two small Arkansas stones I use as slurry stones, one being a coarse Washita stone, the other a Hard Arkansas stone. I also occasionally use a diamond sharpening plate to true the surface of the stone and/or to create a slurry.
Being a natural stone, the exact grit is irrelevant, but depending on technique, the surface, slurry, and amount of water, I can quickly get the results I would expect using an 800 grit synthetic waterstone through to about a 4000 grit synthetic waterstone. With a little extra time and care, I can achieve a more finely polished edge like that from a 6000 – 8000 grit synthetic waterstone, but I will often just switch to a finer stone when that need arises.
I still consider myself in the learning stage of using this type of stone, and as happy as I am with them, I look forward to discovering more of what they are capable of. In my day-to-day work in the shop, it is typically my go-to stone for maintaining edges.
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Stay healthy and safe!