optics - Why is wax brighter?

How can wax be normally darker than paper (absorb more light) but apart of light be lighter (let more light go)?

Answer

This is a question of scatter. Paper is white because the fibers (and fillers) create many refractive index mismatches. When you fill the space between the fibers with wax, you reduce the scatter at these interfaces (because the refractive index "in between" is raised from air to wax). Since paper is thin, the scatter dominates. When you just look at solid wax, it's quite dull for the same reason: there is not a lot of scatter happening inside.

This is why paper saturated with wax will be more translucent.