Sharpest knife made by cooking sand in a microwave oven
youtu.be
youtu.be
My understanding is that the claim is sharpest knife that was made in that fashion, not sharpest overall knife.
The claim here is not that this is the sharpest knife ever and it just happens to be created in a home lab using sand and a microwave. The claim is that among all knifes made from sand, using a microwave, this one is the sharpest - and I am not convinced that you have such a knife, let alone one that is also sharper.
And in about 2 seconds, I can get a really damn sharp "knife" by dropping a wine glass on the floor to induce conchoidal chipping. My foot and hand can attest to them being as sharp or sharper than any surgical instrument or Japanese-angle ground knife.