This is based on simple logic and not any scientific fact, but you need to understand what is happening.
Onions make you cry because they release a chemical (sulphuric acid) into the air that reacts with your eyes. So you need to minimise this as much as you can.
There are a few tips like pop the onion into the freezer for 20 min's or cut it under running water, but neither are very practical.
Now we make no scientific claim, but believe us when we say that we NEVER have any problem with onions irritating our eyes! We did have in the past, so it's not that we are now immune. So below is the most practical solution.
If a knife is really sharp then it is less likely to disrupt the cells of the onions when slicing, thereby not releasing as much of that nasty irritating chemical into the air. Imagine cutting a tomato with a blunt knife, it would squirt juice everywhere wouldn't it? So why would it be so different when cutting through an onion?
Why not let us sharpen your knives for you, and you be the judge. At the very least you will have razor-sharp knives, but we would be really interested if you think we are right or not. Remember we always polish the knife edge, not just sharpen it, so that might have something to do with it as well.
Join us on Twitter ( @knifesharpening ) if you would like some sharpening advice as we will always help you if we can.