Optical illusion

This morning, my friend sent me a video tutorial about drawing optical illusions. It catches my interest that's why I decided to make one. The sad part is while I'm doing it I accendentally marked some parts of it.

Instead of making another one, I decided to put a piece of paper on that areas.

And this is the result.

Materials used:

Vellum board

Marker

Mechanical pencil

Graphite Pencils