Diamond BladeWay back in 2014 we wrote a short article called 'What is the sharpest blade on the planet' and this is the sequel. To save you having to go back and read the original article - the answer is a knife made out of obsidian, as any kid who plays Minecraft could have told you.

Unfortunately in the real world obsidian being used as a knife blade is not that practical as being very brittle, it can leave shards of the blade in whatever it is you are cutting*.

This highlights the essential contradiction with sharp knives - knives made of harder steel, which are capable of being very sharp, are more brittle and will tend to break more easily than knives made of softer steel, so it's all about compromise.

We are of course biased, but we think that the I.O.Shen range combines the best of both worlds as it's made the same way a katana (a samurai sword) is, which neatly gets around some of the problem.

But none of this has stopped people from trying to make the sharpest blade on the planet, and a short review of the evidence on the web has pulled up a couple of interesting approaches.

First off - and you may have seen something on this on our Facebook page - is a guy in Japan who makes knives out of... well, almost anything. So far we've seen a chef's knife made out of underwear, one made out of pasta and one made out of rice. And then one made out of cardboard.

As in this YouTube video, the process of making these knives out of otherwise normal household objects (or food) requires a huge amount of time and effort. But the most important stage is of course the sharpening of the blade and, although it might not at first seem possible, all these unusual knives sharpen up really well in the hands of an expert, rivalling the cutting ability of regular chef's knives.

More serious attempts to make ever sharper knives have also focused on using materials other than metal for the blades. Much of this research has been conducted for blades designed for medical use.

In 1955 a Venezuelan research scientist called Humberto Fernandez Moran invented a blade made of diamond capable of making very precise cuts. These diamond knives are still used for very specific medical purposes, such as eye surgery and in ultramicrotomy, which is the cutting of specimens into incredibly thin slices for analysis under an electron microscope. As you might imagine they are very expensive to make (upwards of US$2000 each).

The other material that makes incredibly sharp blades is glass, and small glass blades are also used in microtomy, although the newer diamond blades can cut anything up to a hundred times more thinly. In practice most electron microscope labs have glass blades and diamond blades and reserve the diamond blades for the final thinnest slicing.

Neither diamond nor glass knives have made it into the kitchen for a number of reasons - the medical blades are actually very small (the blade pictured above is around 2mm across) and need to be handled and sharpened very carefully using special sharpeners made of diamond, plus knives made from either material are very expensive indeed. But who knows? When robots finally take over all the cooking duties, they'll want only the most advanced knives. In the meantime, we recommend I.O.Shen!

*this is the main reason obsidian knives are not approved for use in surgery in the US, despite being incredibly sharp

Image credit: https://commons.wikimedia.org/wiki/File:Diamond_Knife_Blade_Edge.jpg