Depending on the brand you choose, the stones will require different soaking treatments. Some can be stored in water between uses; however, this may not be recommended for others. I prefer to wash my stones after each use and store them dry, as storing them in water allows contaminants from skin and grit to sit on the stone. If you want to pre-soak them, wash them and store in an airtight container or bag.

Both ceramic and water stones typically use water as a lubricant to carry away the swarf and to lubricate the blade as it runs over the stone. Keeping the stone’s surface wet during use is important to avoid clogging or glazing the stone, which reduces its effectiveness. Generally, all water stones need to be soaked before they are used, and only coarse ceramic stones need to be soaked before use, although there are exceptions to this. To determine if a stone needs to be soaked, spray water over its entire surface. If the water immediately disappears, the stone can benefit from a soaking. You may need to soak the stone as long as 10 – 15 minutes. To test if it’s adequately prepared after soaking, remove the stone from the water bath and spray water over the entire surface again. If the water stays, it’s ready. Often, many ceramic stones and extra-fine-grit water stones just need a spritz of water to keep them working.

Ceramic and water stones provide a fresh cutting surface to a tool by breaking away minute fragments of stone in use, exposing fresh media to the tool. A surface is said to be friable if it breaks away more readily compared to another stone. The more friable a stone is, the quicker it wears down during use. Generally speaking, diamond stones are the least friable followed by oil stones, ceramic and then water stones.

This wear, while important to the sharpening process, also erodes the stone during use. Diamond stones don’t need to be flattened, and oil stones rarely need flattening; however, ceramic and water stones require regular flattening. Many of us flatten our stones after each sharpening session so they are ready to go next time around. You may consider this to be overkill, but it doesn’t hurt to check each time to see if it’s necessary. One way to reduce the need for flattening is to use the stone’s entire surface while sharpening. Vary the strokes so that you work across the entire length of the stone.

How to Flatten a Stone

As with most woodworking processes, there are many ways to accomplish the same task. Marking a pattern on the stone with a pencil provides feedback, regardless of method chosen. The simplest method of flattening is to rub two stones together until the pencil lines disappear. While quick and simple, this method can transfer a convex or concave defect to the other stone, resulting in two warped stones. The standard method is to use three stones, alternating until all are flat, as it is impossible for all three to develop concavity or convexity in the process.

Using a surface that is known to be flat is the simplest way to flatten your stones. Here are some options:

• Use silicon carbide grit on a sheet of glass covered by a protective layer of laminate to prevent the glass from becoming dished.

• A sheet of aluminum oxide sharpening media (>100 micron) attached to a flat surface such as glass or granite can also be used.

• An abrasive truing stone is a coarse stone, often made from silicon carbide. It has grooves to remove the slurry. Rubbing the truing stone against the water stone quickly flattens a water stone of any grit. You can put the truing stone on the bench and rub the water stone over it in a swirling motion to cover the entire stone. Alternatively, you can hold one stone in each hand and rub them together, much like rubbing your palms together. Either method is equally effective.

• A coarse diamond plate (200 – 350 grit) is another method many woodworkers use to keep water stones flat. The monocrystalline diamonds are fused to a very flat metal plate, ensuring a completely flat reference surface. Metal-backed diamond stones are generally flatter than plastic-backed ones, so those using this option should consider the metal plates. A benefit of this method is that the coarse diamond plate also provides a grinding stone for when it’s necessary to grind a new primary bevel on a blade – a great way to minimize what you need to buy.

Regardless of the method chosen to flatten your water stones, it is important to find one that matches your workflow. Ceramic or water stones that are not flat will not give you the results you expect from your sharpening investment.

Richard Wile