Shigan, Wiki

The Six Powers, Wiki

Could Mihawk or Shanks Know Rokushiki? : r/OnePiecePowerScaling

Rokushiki, Wiki

Rokushiki Robin action scene 2 - part 2 by Shinjojin on DeviantArt

Chapter Discussion - Rokushiki is based on Haki, Page 7

Chapter Discussion - Rokushiki is based on Haki, Page 5

Honestly Oda probably should have just expanded on Rokushiki instead of creating Haki. He could have definitely made it to where there are techniques that allow you to hit logias and armament

One Piece sound effects - Rokushiki/Shigan v1

Rokushiki Robin 32-1 by Shinjojin on DeviantArt

Shigan, Wiki