Really want to see what I can do with a pen. I had to use a mouse.
I used what looks like bone texture to me and 100 occlusion.
And then to add more to it I used the free version Adobe Photoshop Express. Using filters - Charm4 and Blue combined to add some color and shadowing. I used Invert for a dark creepy version.
Charm4 and Blue
Blue
Charm4
Inverted
Original close up Gif
Original full from ZBrush Core Mini