Drawing Staircase and Sphere Illusion - 3D Trick Art

Drawing Staircase and Sphere Illusion. 3D Trick Art.
Drawing stairs and levitating ball.
Materials used:
Pastell paper: light gray.
H graphit and charcoal pencils (Derwent)
Markers, (Stabilo brand)
White "charcoal" pencil.
Derwent brand.
Grey markers: Letraset PROMARKER.
Soft eraser.