Gradients
Is used to alter the base color of the object based on the angle between the camera and the surface normal (the left side of the gradient is the edge of the object while the right side of the gradient is the center of the object).
Causes the opacity of the object to change according to the angle between the camera and the surface normal. White is opaque while black knots are transparent. Knots at the left side of gradient affect the edge of the object while knots at the right side of the gradient affect the middle of the object.