Russian guys makes knives made of sapphire.
These knives can be easily taken inside the airplane in your handbag, for example if you care about your right to use your knife anywhere you want.
These knives cannot be discovered by any sort of metal-detector, they have none metal parts at all.
Their blades are being made from artificial sapphire, the same material that is being used to make non-scratchable watches by leading Swiss brands. Handles are made of the bone.
Only diamonds exceed it in the hardness, so anybody can easily make his name carved on the airplanes bull's-eye airplane window. It scratches glass without any difficulty and can be sharpened only with special diamond whetstone.