X-ray lenses don&#x27;t really exist, although you can produce focused beams (using either reflection or simply collimation). So, these methods typically involve scanning a sample and measuring some fluorescence line (which gets emitted in roughly all directions).<p>That site doesn&#x27;t mention the spot size, but its likely much larger than the page thickness, so the iron signal from a tilted page probably wouldn&#x27;t differ in a measurable way from having the page perpendicular to the beam. Keep in mind that they require ~24 hours to get even the images shown. Instead it sounds like they rely on compositional differences in the ink from the two sides and look at fluorescence from an element that is only present on one side.<p>It might be possible to get the other side by taking a difference between the Fe and Ca signals (after scaling appropriately).