Here it is. The definitive guide to chopping onions without tears (from Cook’s Illustrated, no. 36, p. 10)
Wear contact lenses: Almost no tears, effectiveness (on a scale of 1 to 10): 10
Wear ski or swim goggles: very effective, but you look like a kitchen terrorist, 9
Burn a candle near the cutting board: Easy to do, worked pretty well, 6.5
Place cutting board near a lit gas burner: worked as well as a candle, 6.5
Refrigerate whole onion for 8 hours: chilled onions, some tears, 5
Refrigerate quartered onion for 8 hours: even colder onions, some tears, 5
Freeze onions for 30 minutes: Coldest onions, some tears, 5
Hold a slice of bread in your mouth: looked silly, didn’t work consistantly, 5
Balance a slice of onion on your head: looked silly, slowed down tears a little, 5
Hold a lit-and-put-out match in your teeth: looked silly, but worked bettter than unlit match, 4
Slice onions under a running faucet: so frustrating the tears didn’t matter, 3
Trim ends off onions and microwave for 1 minute: onions began to cook, minor tear reduction, 3
Hold a toothpick in your teeth: looked silly, cried a lot, 2
Work under an exhaust fan: Not at all effective under a home exhaust, very good under the test kitchen’s professional-caliber exhaust, 2
Tie a scarf around nose and mouth: looked silly, minor tear reduction, 1
Soak onion in ice water for 30 minutes: wet onions, lots of tears, 1
Blanch onions for 1 minute: slimy onions, lots of tears, 1
Wipe cutting board with vinegar: Vinegary onions, lots of tears, 1
Slice onions next to a running faucet: didn’t work, lots of tears, 1
Slice onions in a large plastic bag opened at both ends: awkward and dangerous, plus didn’t stop the tears, 1
Hold an unlit match between your teeth: looked silly, cried a lot, 1
Leave root end on onion intact: didn’t work, 1