Vielsalm Coticule on the other hand generally occurs in much more narrow layers sandwiched between the slate layer and the Belgian Blue layer and thus, it is both less plentiful and more expensive than Belgian Blue stone. Also, Coticule is divided into different grades and sometimes displays blemishes on the surface due to its proximity to the slate layer. Furthermore, it is somewhat harder than Belgium Blue stone and, due to its brittleness, it is bonded to a substrate layer of hard slate prior to sale to prevent the stone from breaking during use.
The video above, from the How To You YouTube channel, explains everything you need to sharpen with a whetstone at home, and the best methods for doing so. Obviously, you’ll need a whetstone (as well as a few other things), and you’ll want to work near your sink or a bucket so you have easy access to water. Fill a container with water, then soak the whetstone in it until it stops bubbling. Inspect your blades for any trouble spots, and get to sharpening using the methods and motions described in the video; making sure to check your progress as you go. We’ve talked about sharpening knives with whetstones before, but this guide is a bit more thorough and the old video has since been removed. 

In addition, the most prized of the natural Japanese Water Stones are quarried in the Narutaki District north of Kyoto, Japan and are commonly available as either bench stones or pocket stones in grits ranging from 120 to 12,000. On the other hand, synthetic water stones are made from Aluminum Oxide and commonly available as either bench stones or pocket stones as well in grits ranging from 220 to 8,000 and, although this is the same abrasive material used to make India Oil Stones, the difference between the two is that the binder that holds the abrasive together enables Water Stones to be much softer than India Oil Stones which, in turn, promotes faster cutting because the worn abrasive material breaks away more quickly and is replaced with fresh, sharp, abrasive material more quickly. In addition, because water stones do not become glazed or loaded with swarf like oil stones can, new abrasive particles are constantly exposed as the stone wears so it continues to cut consistently. Plus, they can be lubricated effectively with water (rather than oil which can ruin some water stones) which combines with the fine particles of abrasive from the surface of the stone to form a slurry which polishes the bevel as the stone cuts. However, it should also be noted that Water Stones do become uneven significantly faster than other types of whetstones although, their softness does make them easier to true again.
One of the most well-regarded natural whetstones is the yellow-gray "Belgian Coticule", which has been legendary for the edge it can give to blades since Roman times, and has been quarried for centuries from the Ardennes. The slightly coarser and more plentiful "Belgian Blue" whetstone is found naturally with the yellow coticule in adjacent strata; hence two-sided whetstones are available, with a naturally occurring seam between the yellow and blue layers. These are highly prized for their natural elegance and beauty, and for providing both a fast-cutting surface for establishing a bevel and a finer surface for refining it. This stone is considered one of the finest for sharpening straight razors.[citation needed]
Your immediate goal is to raise a burr on the side of knife opposite to the side you are sharpening and depending on the steel, the grit of stone and how you are doing, it will be either a very quick process or it will seem like it takes an eternity. Patience here will reward you, believe me. The sharpening process is incomplete with no burr creation on your first stone. (Yes, it is possible to stop at that magic moment without the burr forming but we are not there yet, we don’t even need to go there, ever, I am just mentioning it so those gifted sharpeners will be happy) . Think of the burr as the debris that is making the knife dull being forced down the blade towards the edge and over to the other side of the by your sharpening prowess. You form the burr, that knife will get sharp, no burr, you just need to look at your work. A Loupe is handy here, an inexpensive magnifying device with a light that allows you to see the edge very well, if you are not forming a burr, you are not reaching the edge. (Having a loupe also makes you look cool and scientific, like a Sharpologist).
You want sharpening stones that will be useful for the majority of your edges now, and that will remain useful as you expand both your tools and your sharpening toolkit in the future. Ending up with duplicate stones or ones that are no longer useful as you gain new knives or tools is a waste of money. The goal is to start with something that will stay with you as your needs develop.
Our large selection of stones from many well-known manufacturers will allow connoisseurs to find the ideal stone for their needs. Because all manufacturers formulate their stones to emphasize a different mix of qualities, and because these qualities can vary widely between different stones, most woodworkers choose stones from several manufacturers to build up an optimal set of sharpening stones. Then again, once you get to know the characteristics of certain types of stone, you may find one supplier who will provide all the stones you need. Sometimes this can be an advantage. But there is no one size that fits all; each stone must fit your needs and work style.