You can used India Ink. This give you more of a 'standout' to your color. I personally think its too black though and doesnt look 'exactly' like 18th cent contrast. A little to 'crisp and modern' you might say. What I do,,,,my method,,,, I Draw my art work,,carve it, wet my finger and rub the pencil graphite into the groves. Its not 'shiny back' but more of a matte blackish color. Looks very correct and you dont need to apply anything. Just a bit of spit and rub the lead into you cut you just made with your fingertip. Wipe off the body with ya thumb and presto, you have it done. Move on to next cuts and repeat. You will have a unique horn , complete with DNA! Another thought,,,if you do decide to use india ink, buy a bottle of black, and bottle of brown, and mix 50/50 when you apply it. The brown 'mutes' the black to some degree while remaining really dark. Looks like the 'graphite' color, so why spend money and go to the effort, when all the color you need is right in the end of your pencil. Im working on a carved horn now, and will post some 'step bye step' carving photos if ya'll would like to peek at them. Note,,,I do wash my horns , and often color/age them or 'stress' them,,,so dont worry about getting something you dont wanna touch!,,lol I guess im a stickler bout having things look correct.