Yosef Karo, Shulchan Aruch — Yoreh Deah 10 Other laws of knives
“ It's forbidden to shecht a sick one because it improves [its value] . A gentile's knife that he sharped on his stone (see below #121 end) , or if it was fine and unblemished and he stabbed it in hard earth ten times and then shechted with it, it's permitted. If he shechted with it without kashering, he rinses the cut. If he trims off some, it's praiseworthy. ”
