Review on Hiware 12 Piece Stainless Dinner Knives by Hector Liamsi

At first glance the knives appear to be of decent quality and I wanted them to match my other cutlery. BUT, even though I washed them before use, they got these weird black lines when I cut some butter into them. If you look at the knives, they have this weird black deposit (almost gritty?). I used a toothpick and pulled it all out, soaked and washed them a few times and seemed to get rid of it, but I'm not sure I'll use them as I'm not sure where the black is coming from. Wouldn't recommend it.