Choosing a stone for your knife

- What Kind of Stone?

Basically, a stone needs to cut metal off the edge. The stones below do this well, and for most of us our time would be better spent actually learning how to sharpen than worrying too much about the minor advantages of one stone vs. another. Get the biggest stones you can afford and have room for. Big stones make the job much much easier.

The time-honored stone is the arkansas stone. Soft arkansas stones provide the coarser grits, with harder stones providing finer grits. Many people use oil on these stones, ostensibly to float the steel particles and keep them from clogging the stone. John Juranitch has popularized the notion that oil should absolutely not be used when sharpening, and indeed results from people using arkansas stones without oil have been very positive. However, if you have ever used oil on your arkansas stone, you need to continue using it, or it will clog. If you never put oil on your arkansas stone, you will never need to.

Synthetic stones are very hard, and won't wear like natural stones (a natural stone may get a valley scooped out of it over time). They clean well with detergent-charged steel wool, I use SOS detergent pads, they clean very very fast and very well. I know you're thinking that cleaning with steel wool will cause the stone to shear off the steel wool and fill up the stone even worse! But I assure you that is not the case, for whatever reason SOS pads clean synthetic stones, they do not make the stones dirtier. Spyderco and Lansky are some manufacturers who sell synthetic stones.

Stones with diamond dust embedded in them cut aggressively. You can remove metal very quickly if you need to, but be careful lest you remove too much too fast! DMT, Eze-Lap, and Lansky are some manufacturers who sell diamond-based hones. Some diamond stones have the problem that the diamond dust wears off quickly, leaving you with a useless stone.

Japanese water stones come in some very high grits -- I've seen all the way up to 8000! These stones are very expensive. The stones sit in a water bath, and a slush forms on top that helps the final polish.
Both Japanese water stones and natural stones will eventually dish out in the center with use. To flatten them back out, put some sandpaper on a flat surface and rub the stone top on it. Wet/dry 400 grit sandpaper mounted on a table top or glass is reputed to work well.

- Water or Oil on My Stone?

Basically, the purpose of the stone is to rub against the blade and remove metal. Slippery liquids, like water and especially oil, make the rubbing slicker, causing less metal to be removed, causing sharpening to take longer. On top of that, as your edge is being sharpened on the stone, the oil-suspended metal particles are washing over the edge and dulling it again.

On an arkansas stone, the oil is supposedly needed to float metal particles away from the stone surface, lest the stone clog and stop cutting. Some people on this group have used their arkansas stones without oil or water, and have reported good results. However, if you've already used oil on your arkansas stone, you'll probably need to keep using oil forever on it, because an already-oiled stone will clog up if not kept oiled. If you have a fresh arkansas stone, go ahead and use it without the oil, and things should be okay.

Japanese water stones are the one type of stone that need water. The stones are designed to work with water, and as you sharpen a small amount of the stone's material breaks off and forms an abrasive slurry along the top.

In any case, the bottom line is: use liquid or don't. Using the liquid will make the sharpening process slower and messier, but if you insist on using liquid and are willing to spend more time, that's up to you.

- How Fine Should My Stone Be? Important notes on grits!

The finer the stone, the more polished your edge will become. The rougher the stone, the more the scratches in the edge function as "micro-serrations" (see also the serrated vs. plain edge ). 
Though the actual ontological status of the micro-serrations is debatable (Juranitch says there's no such thing, having looked under a microscope), the serrated effect of the coarser grind is undoubtably there.

The more polished the edge, the better your edge will work for doing push-cut applications like shaving, whittling, peeling an apple, skinning a deer. Also, your cut will be more clean and precise with the polished edge.

A rougher, more micro-serrated edge will work better for slicing-type applications like cutting through coarse rope, wood, etc. The serrations present more edge surface area, and tend to "bite" into the thing being cut.

It is possible to get an edge that will shave hair with a medium (300-400 grit) stone, with practice [I specifically mention stone grits because many manufacturers call the 300-400 grit stones "coarse" rather than "medium"]. The medium stone will have pretty big micro-serrations. In previous version of the FAQ I stated that I find this too rough a finish for my general utility edge. However, I've since found this to be a really nice edge finish for utility work -- it won't shave great, but it does a really nice job on cutting coarse materials.

Anyone should be able to get an edge that shaves hair easily with a fine (600 grit) stone. I find this to be a pretty useful finishing stone, leaving enough micro-serrations for general utility work but still being hair-shaving sharp.

An extra fine stone (1200 grit) should start polishing the edge, and you should end up with a hair-popping sharp edge. This is also a good choice for a general utility finish, especially on a partially-serrated blade, where the serrations can be used when the slightly-polished main part of the blade becomes less effective.

One can buy Japanese water stones with grits up to 8000, which leaves a polished edge that's so sharp, your hairs will jump off your arm when they see the edge coming. I would question this finish on an everyday utility knife which might be called upon to cut through a thick rope or what have you, but it is a finish that works well when a polished edge is called for.

************* IMPORTANT TIP **************** 
Many treatises on sharpening tend to focus on getting a polished, razor-like edge. This is partially the fault of the tests we use to see how good our sharpening skills are. Shaving hair off your arm, or cutting a thin slice out of a hanging piece of newpaper, both favor a razor polished edge. An edge ground with a coarser grit won't feel as sharp, but will outperform the razor polished edge on slicing type cuts, sometimes significantly. If most of your work involves slicing cuts (cutting rope, etc.) you should strongly consider backing off to the coarser stones, or even a file. This may be one of the most important decisions you make -- probably more important than finding the perfect sharpening system!

The tests seem to indicate that you should think carefully about your grit strategy. If you know you have one particular usage that you do often, it's worth a few minutes of your time to test out whether or not a dull-feeling 300-grit sharpened knife will outperform your razor-edged 1200-grit sharpened knife. The 300-grit knife may not shave hair well, but if you need it to cut rope, it may be just the ticket!

If you ever hear the suggestion that your knife may be "too sharp", moving to a coarser grit is what is being suggested. A "too sharp" -- or more accurately, "too finely polished" -- edge may shave hair well, but not do your particular job well. Even with a coarse grit, your knife needs to be sharp, in the sense that the edge bevels need to meet consistently.