MASS is the positive, 3d volumetric ‘heft’ of a subject – it’s like drawing a wireframe but with more feeling. A ‘working metaphor’ is to imagine you are building a huge wrought-iron sculpture in a luminous box of steam, Lines are heavier when close to the viewer, lighter when farther away. Feel the massive weight or heft of the forms while drawing. Mass is the positive counterpart of 3d “space”. Learning to percieve both mass and space will improve overall drawing and is a positive addition to our perception. This is a necessary skill for designers who wish to become strongly adept at “sculpting space”.