Every time you use a knife to cut something, the edge loses its sharpness and becomes blunt.
This happens because the edge sticks out and cuts a lot of microscopic bits of metal with each slice. It also risks bending the blade.
The only way to keep your knives sharp is to use them correctly and store them properly. By learning the common errors that make knives go dull, you can keep them sharp for a longer period of time.
Cutting Test
The cutting test is a quick and easy way to tell if your knife is sharp. It involves holding a piece of paper in your hand and slicing it crosswise. If the blade cuts smoothly and easily without too much pressure, it’s considered sharp enough for everyday use.
However, if the cut is difficult to make or the knife gets stuck, it needs sharpening. Moreover, you may notice imperfections such as ragged edges or bits of fruit left behind.
Another simple way to tell if your knife is sharp is to rub your finger along the edge of it. It should be done a little off-center so that you can get more of an accurate feel for how sharp the edge is.
Light Reflection Test
The light reflection test is a great way to see whether your knife edge is sharp enough to cut with. If you can see a thin blue or silver line when observing the blade edge with a light source behind it, it means that there are no nicks or dents in the cutting edge.
To perform this test, turn the knife over so that its cutting edge is facing upwards. If you can see glinting spots where the blade meets the light, it’s likely that the edge is dull.
If you can’t see any glinting spots, the edge is probably damaged and needs to be re-sharpened. Use a stone with a grit from 0 to 220 grain size (extra coarse to coarse), this will quickly remove any imperfections in the blade edge.
This technique is a lot less reliable than the BURR (Secret #6) method of visual inspection, which only reveals a folded burr on very fine edges. Regardless, I never rely on visual tests for edge quality or indications of a full apex; the BURR is my best test of edge quality.
Burr Removal Test
Burrs are the collection of tiny bits of metal that accumulate on the blade during sharpening. They are an essential part of the knife sharpening process and must be removed before the knife is fully smooth and free of waste metal.
To identify a burr, run your finger down the edge of the blade and feel for anything that catches. If it does then there is a burr on the opposite side of the blade and you will need to work on that side of the knife to remove it.
Fingernail Test
A simple and reliable test to check the sharpness of a knife is to tap it against a fingernail. A sharp blade will bite in and leave a mark on the nail, while a dull one will glide over it.
Another quick test is to slide a paper across the cutting edge of the knife. If it’s sharp, the paper will slice easily with just the weight of the knife.
In addition, a sharp knife will cut a clean line on the paper without any jagged or missed spots. A dull knife will be ragged or slip right off the paper.
Like hair, fingernails are made from a protein called keratin. Drug and alcohol biomarkers are trapped in the keratin fibers.