Chromium Oxide pastes and diamond sprays are the easiest method to keep your razor sharper for longer. We’ve had several questions regarding what are the best practices with regards to these sharpening compounds; and sharpening compounds these are. They are used to slightly sharpen the edge and should not be used for daily stropping. While there is heated debate as to whether the edge degrades over several uses, using pastes/sprays undoubtedly makes a dull razor a little sharper. In our experience, while pastes/sprays prolongs the need for sharpening on stones, the edge from stones is still superior (a good explanation of why can be found here). The two main types of sharpening compounds are chromium oxide (which comes in a crayon, powder, or paste form) and diamond sprays.
Chromium Oxide (aka Crox)
Whichever medium of chromium oxide you use, the best stropping medium we have found is plain old cotton. A close second is linen, followed by the rough side of a leather strop. The smooth (good) side of a leather strop is also a decent medium but ruins the strop for daily stropping. If you don’t happen to have any of these, balsa wood is an acceptable medium. We haven’t had much success with crox and wool felt; your mileage may vary. Best practice is to apply the chromium oxide to the opposite side of the cotton/linen/leather you use for your daily stropping. This way you can flip the piece over when you need to touch up the razor, but at all other times you use the clean side for daily stropping.
Chromium oxide used for sharpening applications is normally found in .5 micron grit size. Grit size is used loosely because both grit and micron are different terms of measurement. .5 microns is generally regarded as being the equivalent of 20,000 to 35,000 grit. The .5 micron size is generally well liked and most users report a smooth shave. We recommend purchasing .5 micron if you wish to use crox.
Diamond sprays only come in one medium: a spray bottle of diamond powder suspended in a liquid. To use diamond spray, very sparingly spray the diamonds over the length of the stropping medium you wish to use. In our experience wool felt is simply superior to all other materials. Cotton and linen come in second place, but due to their more rigid and less cushioning surface tend to produce a harsher edge. The back of a leather strop can also be used. The smooth side and balsa wood did not produce very good results for us.
Unlike crox, diamond sprays come in a wide variety of sizes. From .125 microns to 5 microns and up, diamond sprays can be had in many different micron ratings. The .25 micron is as small as we recommend. In fact, we find the .25 micron to be pretty harsh on the face. We should also take the time to note that many people find the chromium oxide to be smoother than diamonds; even in equivalent micron sizing. This is probably due to the nature of the cutting particles. Where crox particles are generally circular in form, diamonds are crystalline by nature. These crystals invariably produce more jagged cuts in the steel than the circular crox particles. That said, diamond pastes come in a smaller micron rating. Choose accordingly.
Crox v. Diamond Sprays
There is much debate over which one is better. The general consensus is that diamond sprays are sharper, but harsher, and crox is smoother, but duller. As I said above, this is due to the nature of the cutting molecules. However, the medium plays a large role in how the spray/paste affects the edge. For example, using crox on balsa wood will make the edge harsher, and a bit sharper. That said, the end result isn’t very pleasant compared to better options. Crox on a smooth leather strop will give you that sharp razor you want, but you lose a bit of the smoothness. My favorite is crox on cotton. Sharp enough for daily shaving, but still smooth and irritation free.
Diamond sprays are inherently sharper than crox. Crox only comes in .5 micron sizing at its finest grit. Diamond sprays come in a bewildering array. From .125 to 16 microns, you can find a diamond spray or powder for whatever application you need. .25 micron diamond spray is generally the smallest your going to find in spray form. At least one seller sells the .125 micron size; yet he’s the only one I’ve found so far which puts his claim into question. Either case, the diamond spray allows you to go sharper. Yet, you get a harsh edge because of the way the diamonds cut into the steel, as I said above.
To ameliorate this problem, straight razor users have come up with a variety of methods to combat the harshness. The most popular method by far is using a felt medium. And honestly, until we come up with something better; felt is as good as it gets. Yet, felt comes with its own problems. The very reason felt works in softening the edge is because the felt is so cushioning. Press down on the felt and it dips a little. Not so with cotton or balsa wood. Okay the balsa will compress if you press hard enough. But that is the inherent problem with diamond sprays and felt. The felt allows much more deflection in the cutting surface than any other method. Now, this deflection creates a more obtuse edge angle, but not by much. Perhaps over time the angle’s obtuseness becomes evident, but not for a while. Even then, you can still shave with a more obtuse edge angle.
So, in the end, the diamond is sharper due to the smaller micron sizes available. Yet, the crox is more than sharp enough and is smooth. In the end, it doesn’t really matter, both methods are eclipsed by physical stones and actual honing. Yet, both methods produce a serviceable edge that will get the job done.