The Hero Arts stamp isn't necessarily designed to give a truly solid, blacked out impression. If you look at it closely (well, maybe not now, since it's been sanded), you'll see teeny tiny dots that make up the "solid" area. This leaves the density of the sky up to the stamper. I have that stamp and use it with chalk ink. Sometimes I just do a thin layer to get a more mottled look, other times I really put on a nice thick layer of ink to get a more dense look. Good luck!