Sharpest knife made by cooking sand in a microwave oven
youtu.be
youtu.be
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.
My understanding is that the claim is sharpest knife that was made in that fashion, not sharpest overall knife.
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.