If a solid cylinder of glass or clear plastic is placed above the words lead oxide and viewed from above as the lead appears inverted but the oxide does not?

The phenomenon you are describing is due to the difference in refractive indices of the glass or clear plastic and the surrounding air. When light passes from air into a denser medium like glass or plastic, it bends towards the normal line, and when it exits the medium, it bends away from the normal line. This bending of light causes the image to appear inverted when viewed through the glass or plastic cylinder. The lead oxide and lead likely have different refractive indices, causing the inversion effect to only occur for one of the Words.