Hello just thought i drop a note, 8) the Ivory i get is from Alaska , from a walrus/ tusk , I am part Eskimo and it is a native Art form (Ivory Carving) the Ivory is a byproduct from subsistence life style.
You're well along with graphite and paint. What about charcoal? Or pen and brush from a bottle of carbon ink? I think working with these will give you a perspective on tone and line that will push you to the next level.