This week we have two Prismacolor Pencil interpretations of a nice old stone-ware jug (actually a bottle) and a small glass jar. The three dimensional forms you see here are the result of careful observation and accurate renditions of shape, color, shade, shadow and reflection. In the first version on the right we see these three objects straight-on at eye level with no sense of form derived from linear perspective. If this were a line drawing it would essentially consist of flat shapes outlined.
(Tho' not the essential point of this post, a hint of depth is seeing shapes overlapping.)
In this second drawing we perceive form because of the same accurate representation as above but with the addition of linear perspective. We are looking from a slightly higher viewpoint so can see the oval shapes in the openings of the jar and in the shoulder and base lines of the bottle. While we can see the complete top edge of the jar, our eyes follow the jug's shoulder line as it disappears around the "corner" on the right side and we complete the oval in our mind as it passes behind and reappears running toward us on the left. We understand this as an indication of 3D form.
Our experience with this world says that light on one side of an object usually produces a shadow side, a curved object's shading progresses from light to dark and a highlight is the reflection of a light-source. Our hands confirm that perception of form when we reach out and hold an object. When the right marks are presented on a flat surface in an appropriate way, we believe!
"What we call art would seem to be specialist artifacts for enhancing human perception." Marshal McLuhan
"In order for the light to shine so brightly, the darkness must be present." Sir Francis Bacon