A "diamond" ring, which could be fake is immersed in oil $(n=1\mathrm{.}43).$ Light reflected from the diamond$-$oil interface is totally polarized at an angle of $49\mathrm{.}0$ degrees from the perpendicular. Is this a fake diamond ring? $n=2\mathrm{.}42$ for diamond. $n=1\mathrm{.}65,$ fake, most likely glass.