Well, there are a number of ways to cut an onion without tears. The most common tips include chewing something like gum while cutting onions or lighting a candle nearby etc. If you don’t have a candle, it can be helped with your gas burner turned on.
Some tips even suggest people to wear a pair of swim goggles to cut onions in your kitchen.
My way of cutting an onion without crying
This is what I normally do when I need to cut two or three onions.
Take an onion and quickly chop off both its ends with a sharp knife and throw it into a bowl of water (See the first half of the picture below). Do the same for all onions.
Wet your knife and chop board once. Pick one onion, peel off its skin with a vertical line drawn with the knife. Do the same for the rest of your onions.
Make the onions into two half and keep its cut surface down. Work on each half swiftly to chop it at the desired width from one end to the other without allowing them to split apart (See the second half of the picture above)
This whole process explained gets completed within a few seconds and guarantees no or very minimal tears. Basically, these steps make sure that very little eye irritants are allowed to escape into the air thereby minimizing tears caused.
Why do onions make you cry?
When you cut an onion, it releases certain compounds that spread into the air. These cause the lachrymal glands in the eyes to become irritated thereby releasing tears.
If you are interested in learning more on this chemical reaction, please refer to this literature.