Mass is the amount of matter a certain object has. Depth is the distance from the topmost part of a certain object that runs down to it's most bottom part. These two terms are both related in a way, especially in making works of art and as well as in science experiments.
refer to these websites for more info on both illusions 1- thevirtualinstructor.com/hatchingcrosshatching.html 2- www.udel.edu/artfoundations/beg_paintingtechniques.html
