Transparent solid objects are also defined by the specific ways they distort the images of things seen through them. A transparent sphere always inverts the image of whatever is behind it. A transparent vertical cylinder causes images to be seen in reverse, while a horizontal one causes images to invert. Images seen through a solid transparent cone appear triangulated and reversed. Cubes shift what is seen through them slightly to the side or above or below. A window can be thought of as a slice of a cube visually shifting the position of objects seen through it; the thicker the glass, the greater the shift.
Transparent hollow objects share all of the characteristics of transparent solid objects, but the secondary highlights are seen only in the hollow object's thin walls. These walls distort what is seen behind them, but not as much as transparent solids do. In most cases the distortion is a shifting of background edges, similar to the distortion caused by transparent cubes. If the walls of the transparent hollow object curve or vary in thickness, the contour of what is seen behind the object will appear to bend.
If we look through the middle of an empty glass jar, we can see what is behind it. But if we look at its sides, we cannot see through as well, because there the glass is thicker and more opaque. We identify a hollow transparent object by seeing its edges, its primary highlight, and the distortion at its edges of what is seen through it.
At left is a hollow transparent sphere, at whose edges background images appear distorted. At right is a solid transparent sphere, which inverts images seen through it.
A solid transparent cone reverses and triangulates images seen through it. A hollow cone just distorts the images seen through it at its edges.
At the left is a hollow transparent cylinder, at whose edges the background appears distorted. At the right is a solid transparent cylinder, through which background images appear in reverse. If this solid cylinder were horizontal, the background images seen through it would be inverted.
A solid transparent cube shifts the image of what appears behind it from side to side or up and down, depending on the angle and thickness of the cube. A hollow transparent cube does the same, only less so.
The edges of a hollow transparent object distort the image of whatever is viewed through it. The thicker the walls of the object, the greater the distortion.
When we look at an empty glass, we look through less glass in its middle than we do at its sides. There, the glass seems to form nearly opaque "lines" that define its silhouette.
What's wrong with this picture? Hollow transparent objects are most clearly defined by their edges. The glass at for right seems to float in front of its mate because of the way its edges have been drawn.