Print on a sheet of paper appears raised when seen through a glass slab. Explain why?
Light passing through a slab a glass actually can go through many reflections. Let us start with a letter A printed in blue ink with a glass plate on top. The light from the ink penetrates the glass to the outer surface. There some of the passes through to the air, but some of it is reflected back to the back surface. When it hits the back surface of the glass some of it passes through and some is reflected forward again. The process is repeated. What one sees are two images of the letter: the original light and one from the first set of reflections. Those of multiple reflections beyond the first set are too faint to see.
The two sets of images are offset slightly giving it a stereo effect which our eyes interpret as raised print.