Modern synthetic stones come in many different types and combinations of elements. Sharpening stones share a similar composition, which includes an abrasive material and a bonding agent. The abrasive is a ceramic powder made of silicon carbide or aluminum oxide. Each compound has its characteristics, such as wear resistance, cutting speed, and hardness of the stone. Synthetic stones have gained popularity due to their availability and low cost of production. Some believe that synthetic stones provide better results than natural stones.
Roy Underhill would probably disagree with this opinion. In his book The Wood Wright's Companion, he says that stones found in a quarry or a mine can replace modern products. Very possible that it is the case. I have no experience with natural sharpening stones yet. I tried to explore his point of view. Natural stone seemed to me more wear-resistant and durable. No bonding agent could withstand thousands of years under the tremendous pressure underground. But also, when working with natural sharpening stones, it's hard to tell what grit they have. Synthetic stones are made from a ceramic compound that is grounded into crumbs. In this way, the crystal size of the abrasive compound is controlled during production. With natural stones, the grit is determined by the general feeling and the results after use. A natural stone must go through treatment before being used for sharpening. After quarrying, stones are leveled for subsequent use. One option is to use a similar stone and rub them against each other. One of the things we are all facing when sharpening a whetstone – it gets out of shape. If you use a stone for a long time, it changes its shape, and instead of being perfectly flat when new, it now has all sorts of bumps and waves on the surface. Is it a bad thing? I don't think so. Let me explain.
Step by step we get there
Knives and scissors can be hard to get sharpened. Curved knives, for example, cannot be sharpened on a flat whetstone due to the shape. Serrated knives, on the other hand, will ruin the stone, leaving marks on the flat surface. You may want to use a round file or a home electric grinder to sharpen serrated or curved knives. Speaking of flat stones (but the flat Earth), in my experience, flattening tools have never found room in my inventory. When I use a new whetstone, I work from the center of the stone to the side, keeping even wear. If I see one of the corners is higher than the overall stone level, I flat it out with a knife. There are a few techniques to sharpen knives using a stone, and every method works if it gives you desired results. One concept may open new doors in the art sharpening for you: Newton told us that action always has an equal counteraction. Each movement of the knife on the stone not only sharpens the tool itself but also changes the shape of the stone. So if you don't allow uneven wear on the whetstone during sharpening, you can avoid using leveling tools. In this way, we prolong the life of the sharpening stone, as we do not waste material on leveling the surface of it.
If your sharpening stone is not flat, you can still use it. By changing the angle of the knife when sharpening, you will achieve results just as good as with a flat stone
Each of us uses sharpening stones in the way that suits us best. We select the whetstones according to the need. When using synthetic stones, I choose 1000 to 6000 grit stones. If the knife blade is not too worn or damaged, 1000 grit will convey a new cutting edge without the risk of removing too much metal from the knife. After making the cutting edge, I polish it with 3000 and 6000-grit stones.
It is more about your style that you find attractive. It all comes with experience, just like everything else.