How sharp is an obsidian knife

Methods for testing sharpness

There are innumerable ways to test the sharpness of a knife or cutting tools in general. Practical as well as unusual methods are outlined below.
In this test, the knife is placed with the back of the knife on a solid surface (table top) and a tomato is dropped on the cutting edge. If the tomato is neatly cut in half, you have a really sharp knife in your hand, otherwise a big mess on the table top-

Test conclusion: spectacular, but not suitable for everyday use.

Suitable for everyday use - cutting a tomato

A good test to assess the sharpness of knives without a serrated edge or a saw edge. Blunt knives crush a tomato rather than cut it. Or the knife slips on the tomato because the knife cannot cut the tough skin of the tomato. If you can cleanly cut even soft tomatoes into 2 mm thin slices, you have a really sharp knife in your hand.

Test conclusion: suitable for everyday use, objective assessment of the sharpness possible.

Always available - the hair test

During the hair test, the knife is guided along the hair on the back of the neck at a slight angle. If the cutting edge catches on the hair, the knife is very sharp.

Test conclusion: (mostly) available, but not scalable, only statement very sharp or not very sharp.

Practical - scraps of paper

You take a sheet of copier (paper) and cut strips from it. If you manage to cut evenly thin strips of paper regularly, the knife is sharp. If the paper test succeeds with thinner newspaper, the knife is very sharp. The paper test is a good way of assessing the sharpness along the entire cutting edge. The areas that cut poorly or even hook in certain places during the pull cut are not sharp enough or the cutting edge has even broken off a little.

Test conclusion: suitable for everyday use and always available, objective assessment of the sharpness possible.

Masterly - recognizing reflections

This test works without aids, but requires good eyesight. The sharpness of a cutting edge can also be judged purely optically. A sharp edge cannot be seen directly with the naked eye. However, metallic surfaces reflect light and these reflections can be seen. And the cutting edge, no matter how thin it is, reflects light. The more blunt the cutting edge, the larger the reflective surface and the stronger the light reflections. The degree of reflection is a measure of the sharpness of a cutting edge. A blunt edge reflects a lot of light, a sharp edge reflects little light and a very sharp edge reflects as little light as possible.

Conclusion: Masterful, always available, but a lot of practice required.

Insightful - the cucumber test

In the cucumber test, like in the tomato test, thin slices are cut from the cucumber. The thinner these slices can be cut cleanly, the sharper the cutting edge. Blurred areas on the cutting edge can also be easily identified due to the additional effort required. And even with large knives, the sharpness of the cutting edge can be assessed over the full length of the blade in the cucumber test.

Conclusion: informative, practical, easily reproducible.

Playful - The self-cut rubber ring

In this test, a rubber ring is placed around the blade, tensioned against the cutting edge and then released. A very sharp knife will cut the rubber ring, a less blunt blade will not. This method is only suitable for assessing the sharpness at one point on the cutting edge. In order to assess the sharpness along the entire length of the blade, numerous tests are required at different points along the cutting edge - very laborious.

Conclusion: playful. Assessment of the entire cutting edge is only possible with great effort.

Impressive - the split hairs

In this test, a human hair is passed lengthways against the cutting edge. This hair can be split with a very sharp knife.

Conclusion: impressive, but only selective statements possible, impractical.

Dangerous - the finger test

Some claim that the sharpness of a cutting edge can also be felt when the thumb is pressed on the blade or stroked across the cutting direction (scraping cut) along the cutting edge. In the finger test, however, the sharpness can only be assessed subjectively without risk, as it depends on the thickness of the (corn) skin and the personal pain sensation. Since the finger test does not allow an objective assessment of the sharpness and is also dangerous to use, this test can only be discouraged. There are better tests that can be carried out safely, such as the cucumber and tomato test or the paper snippet test.

Conclusion: dangerous! Can only be discouraged.

For men only - shaving your forearms

In the shaving test, the knife is used like a razor. The body hair is preferably shaved on the forearm. You can shave with sharp knives, but not with blunt knives. This method requires a certain amount of body hair and can therefore often only be used by men. Many people will eventually have a shaved left (right-handed) or right (left-handed) forearm ...

Conclusion: only for men! Suitable for everyday use only to a limited extent.