Cylindrical lens of lucite with words "DIOXIDE GLASS".

Cylindrical lens of Lucite with words 'DIOXIDE GLASS'. A solid cylinder of clear Lucite is mounted in a wooden holder. Mounted on the wood base beneath the cylinder is a white card that has the words DIOXIDE GLASS printed on it.. The word DIOXIDE is printed in blue; the word GLASS is printed in red. When read from the side (not through the cylinder), DIOXIDE GLASS can be read in the normal fashion. When viewed through the Lucite cylinder, the blue DIOXIDE still reads in the normal way, but the red GLASS now is inverted. The purpose of this demo is to make the students think. Do the colors red and blue, the index of refraction, or the optical properties of the cylinder have anything to do with the phenomena? Of course, the word 'DIOXIDE' is symmetrical with respect to the horizontal axis, whereas the word 'GLASS' is not.