HP and the Crystal Skull

As the Indiana Jones movie with Crystal Skulls delights audiences I found the website of the Mitchell-Hedges skull and it talks of the experiments scientists at HP Labs conducted on it in 1970.

"In one of the tests the skull was submersed in a glass chamber containing benzyl alcohol of exactly the same density and refractive index as pure quartz. As the skull was lowered into the tank it seemed to disappear. This proved that it was made of the most incredibly pure type of quartz. But not only was it pure, it was also natural “rock crystal supplied by the earth”. Polarized light was directed at the skull in its chamber and vague shadows or ‘veils’ then appeared, which showed that the skull was of natural origin. These shadows, tiny variations in the growth pattern of the crystal, somewhat akin to rings on a tree, are removed in the precisely controlled environment of manufactured quartz."